diff --git a/src/blockstore/blockstore_flush.cpp b/src/blockstore/blockstore_flush.cpp
index a83699ef..6b4d3a97 100644
--- a/src/blockstore/blockstore_flush.cpp
+++ b/src/blockstore/blockstore_flush.cpp
@@ -224,7 +224,7 @@ resume_1:
         goto resume_0;
     }
     assert(!end_wr->next() && end_wr->entry_type == (BS_HEAP_BIG_WRITE|BS_HEAP_STABLE));
-    clean_loc = end_wr->location;
+    clean_loc = end_wr->big().location;
     if (bs->log_level > 10)
         printf("Compacting %jx:%jx l%ju .. l%ju (last l%ju)\n", cur_oid.inode, cur_oid.stripe, end_wr->lsn, begin_wr->lsn, compact_lsn);
     flusher->active_flushers++;
@@ -241,8 +241,6 @@ resume_1:
     {
         overwrite_start = read_vec[0].offset;
         overwrite_end = read_vec[read_vec.size()-1].offset + read_vec[read_vec.size()-1].len;
-        big_start = overwrite_start < end_wr->offset ? overwrite_start : end_wr->offset;
-        big_end = overwrite_end > end_wr->offset+end_wr->len ? overwrite_end : end_wr->offset+end_wr->len;
     }
     read_to_fill_incomplete = false;
     if (bs->dsk.csum_block_size > bs->dsk.bitmap_granularity)
@@ -402,8 +400,7 @@ void journal_flusher_co::fill_partial_checksum_blocks()
     {
         read_to_fill_incomplete = true;
         uint32_t blk_begin = (hole_start - hole_start % bs->dsk.csum_block_size);
-        blk_begin = (blk_begin < big_start ? big_start : blk_begin);
-        uint32_t blk_end = (blk_begin + bs->dsk.csum_block_size) > big_end ? big_end : (blk_begin + bs->dsk.csum_block_size);
+        uint32_t blk_end = (blk_begin + bs->dsk.csum_block_size);
         uint32_t copy_flags = COPY_BUF_CSUM_FILL | (bs->perfect_csum_update ? 0 : COPY_BUF_SKIP_CSUM);
         if (!read_vec.size() || read_vec.back().copy_flags != copy_flags ||
             read_vec.back().offset != blk_begin || read_vec.back().len != blk_end-blk_begin)
@@ -412,7 +409,7 @@ void journal_flusher_co::fill_partial_checksum_blocks()
                 .copy_flags = COPY_BUF_DATA | copy_flags,
                 .offset = blk_begin,
                 .len = blk_end - blk_begin,
-                .disk_loc = end_wr->location,
+                .disk_loc = end_wr->big().location,
                 .disk_offset = blk_begin,
                 .disk_len = blk_end - blk_begin,
                 .buf = (uint8_t*)memalign_or_die(MEM_ALIGNMENT, blk_end - blk_begin),
@@ -467,7 +464,7 @@ int journal_flusher_co::check_and_punch_checksums()
             assert(wr);
             uint32_t *csums = (uint32_t*)(wr->get_checksums(bs->heap)
                 + (vec.disk_offset/bs->dsk.csum_block_size)*(bs->dsk.data_csum_type & 0xFF)
-                - ((wr->type() == BS_HEAP_BIG_WRITE) ? 0 : (wr->offset/bs->dsk.csum_block_size)*(bs->dsk.data_csum_type & 0xFF)));
+                - ((wr->type() == BS_HEAP_BIG_WRITE) ? 0 : (wr->small().offset/bs->dsk.csum_block_size)*(bs->dsk.data_csum_type & 0xFF)));
             bs->heap->calc_block_checksums(
                 csums, vec.buf, wr->get_int_bitmap(bs->heap), vec.disk_offset, vec.disk_offset+vec.disk_len, false,
                 [&](uint32_t mismatch_pos, uint32_t expected_csum, uint32_t real_csum)
@@ -524,7 +521,7 @@ int journal_flusher_co::check_and_punch_checksums()
     {
         if (vec.copy_flags & COPY_BUF_CSUM_FILL)
         {
-            uint32_t csum_off = (vec.offset/bs->dsk.csum_block_size - end_wr->offset/bs->dsk.csum_block_size) * (bs->dsk.data_csum_type & 0xFF);
+            uint32_t csum_off = vec.offset/bs->dsk.csum_block_size * (bs->dsk.data_csum_type & 0xFF);
             bs->heap->calc_block_checksums((uint32_t*)(csums+csum_off), vec.buf, bmp, vec.offset, vec.offset+vec.len, true, NULL);
         }
     }
@@ -561,8 +558,6 @@ bool journal_flusher_co::calc_block_checksums()
             bitmap_set(bmp, vec.offset, vec.len, bs->dsk.bitmap_granularity);
         }
     }
-    end_wr->offset = big_start;
-    end_wr->len = big_end-big_start;
     // Update block checksums
     size_t i = 0;
     while (i < read_vec.size() && !(read_vec[i].copy_flags & COPY_BUF_CSUM_FILL))
@@ -576,10 +571,10 @@ bool journal_flusher_co::calc_block_checksums()
             end = read_vec[i].offset+read_vec[i].len;
             i++;
         }
-        // `read_vec` should contain aligned items (with respect to big_start/big_end), possibly split into pieces
-        assert(!(start % bs->dsk.csum_block_size) || start == big_start);
-        assert(!(end % bs->dsk.csum_block_size) || end == big_end);
-        uint32_t csum_off = (start/bs->dsk.csum_block_size - big_start/bs->dsk.csum_block_size) * (bs->dsk.data_csum_type & 0xFF);
+        // `read_vec` should contain aligned items, possibly split into pieces
+        assert(!(start % bs->dsk.csum_block_size));
+        assert(!(end % bs->dsk.csum_block_size));
+        uint32_t csum_off = start/bs->dsk.csum_block_size * (bs->dsk.data_csum_type & 0xFF);
         bs->heap->calc_block_checksums(
             (uint32_t*)(csums+csum_off), bmp, start, end,
             [&](uint32_t start, uint32_t & len)
diff --git a/src/blockstore/blockstore_heap.cpp b/src/blockstore/blockstore_heap.cpp
index 66e3189e..4258216a 100644
--- a/src/blockstore/blockstore_heap.cpp
+++ b/src/blockstore/blockstore_heap.cpp
@@ -20,7 +20,7 @@
 #define HEAP_INFLIGHT_DONE 1
 #define HEAP_INFLIGHT_COMPACTABLE 2
 
-#define MIN_ALLOC (sizeof(heap_object_t)+sizeof(heap_write_t))
+#define MIN_ALLOC (sizeof(heap_object_t)+sizeof(heap_tombstone_t))
 
 static constexpr uint32_t heap_entry_type_pos = 4;
 
@@ -31,14 +31,15 @@ heap_write_t *heap_write_t::next()
 
 uint32_t heap_write_t::get_size(blockstore_heap_t *heap)
 {
-    return (sizeof(heap_write_t) +
-        (type() != BS_HEAP_TOMBSTONE
-            ? heap->dsk->clean_entry_bitmap_size
-            : 0) +
-        (type() == BS_HEAP_BIG_WRITE
-            ? heap->dsk->clean_entry_bitmap_size
-            : 0) +
-        get_csum_size(heap));
+    if (type() == BS_HEAP_BIG_WRITE)
+    {
+        return sizeof(heap_big_write_t) + heap->dsk->clean_entry_bitmap_size*2 + get_csum_size(heap);
+    }
+    if (type() == BS_HEAP_TOMBSTONE)
+    {
+        return sizeof(heap_tombstone_t);
+    }
+    return sizeof(heap_small_write_t) + heap->dsk->clean_entry_bitmap_size + get_csum_size(heap);
 }
 
 uint32_t heap_write_t::get_csum_size(blockstore_heap_t *heap)
@@ -58,21 +59,30 @@ uint32_t heap_write_t::get_csum_size(blockstore_heap_t *heap)
         // However, we only use part of it related to offset..offset+len
         return heap->dsk->data_block_size/heap->dsk->csum_block_size * (heap->dsk->data_csum_type & 0xFF);
     }
-    return ((offset+len+heap->dsk->csum_block_size-1)/heap->dsk->csum_block_size - offset/heap->dsk->csum_block_size)
+    return ((small().offset+small().len+heap->dsk->csum_block_size-1)/heap->dsk->csum_block_size - small().offset/heap->dsk->csum_block_size)
         * (heap->dsk->data_csum_type & 0xFF);
 }
 
 bool heap_write_t::needs_recheck(blockstore_heap_t *heap)
 {
-    return len > 0 && lsn > heap->compacted_lsn &&
-        (type() == BS_HEAP_SMALL_WRITE || type() == BS_HEAP_INTENT_WRITE);
+    if (type() != BS_HEAP_SMALL_WRITE && type() != BS_HEAP_INTENT_WRITE)
+    {
+        return false;
+    }
+    return small().len > 0 && lsn > heap->compacted_lsn;
 }
 
 bool heap_write_t::needs_compact(blockstore_heap_t *heap)
 {
-    return (entry_type == (BS_HEAP_SMALL_WRITE|BS_HEAP_STABLE) ||
-        entry_type == (BS_HEAP_INTENT_WRITE|BS_HEAP_STABLE) && heap->dsk->csum_block_size > heap->dsk->bitmap_granularity &&
-        ((offset % heap->dsk->csum_block_size) || (len % heap->dsk->csum_block_size)));
+    if (entry_type == (BS_HEAP_SMALL_WRITE|BS_HEAP_STABLE))
+    {
+        return true;
+    }
+    else if (entry_type == (BS_HEAP_INTENT_WRITE|BS_HEAP_STABLE) && heap->dsk->csum_block_size > heap->dsk->bitmap_granularity)
+    {
+        return ((small().offset % heap->dsk->csum_block_size) || (small().len % heap->dsk->csum_block_size));
+    }
+    return false;
 }
 
 bool heap_write_t::is_compacted(uint64_t compacted_lsn)
@@ -82,8 +92,15 @@ bool heap_write_t::is_compacted(uint64_t compacted_lsn)
 
 bool heap_write_t::can_be_collapsed(blockstore_heap_t *heap)
 {
-    return !heap->dsk->csum_block_size || heap->dsk->csum_block_size == heap->dsk->bitmap_granularity ||
-        !(offset % heap->dsk->csum_block_size) && !(len % heap->dsk->csum_block_size);
+    if (type() == BS_HEAP_BIG_WRITE || type() == BS_HEAP_TOMBSTONE)
+    {
+        return false;
+    }
+    if (!heap->dsk->csum_block_size || heap->dsk->csum_block_size == heap->dsk->bitmap_granularity)
+    {
+        return true;
+    }
+    return !(small().offset % heap->dsk->csum_block_size) && !(small().len % heap->dsk->csum_block_size);
 }
 
 bool heap_write_t::is_allowed_before_compacted(uint64_t compacted_lsn, bool is_last_entry)
@@ -97,34 +114,36 @@ uint8_t *heap_write_t::get_ext_bitmap(blockstore_heap_t *heap)
 {
     if (type() == BS_HEAP_TOMBSTONE)
         return NULL;
-    return ((uint8_t*)this + sizeof(heap_write_t));
+    return ((uint8_t*)this + (type() == BS_HEAP_BIG_WRITE ? sizeof(heap_big_write_t) : sizeof(heap_small_write_t)));
 }
 
 uint8_t *heap_write_t::get_int_bitmap(blockstore_heap_t *heap)
 {
     if (type() != BS_HEAP_BIG_WRITE)
         return NULL;
-    return ((uint8_t*)this + sizeof(heap_write_t) + heap->dsk->clean_entry_bitmap_size);
+    return ((uint8_t*)this + (type() == BS_HEAP_BIG_WRITE ? sizeof(heap_big_write_t) : sizeof(heap_small_write_t)) + heap->dsk->clean_entry_bitmap_size);
 }
 
 uint8_t *heap_write_t::get_checksums(blockstore_heap_t *heap)
 {
     if (!heap->dsk->csum_block_size)
         return NULL;
-    if (len && (type() == BS_HEAP_SMALL_WRITE ||
-        type() == BS_HEAP_INTENT_WRITE))
-        return ((uint8_t*)this + sizeof(heap_write_t) + heap->dsk->clean_entry_bitmap_size);
+    if ((type() == BS_HEAP_SMALL_WRITE || type() == BS_HEAP_INTENT_WRITE) && small().len > 0)
+        return ((uint8_t*)this + sizeof(heap_small_write_t) + heap->dsk->clean_entry_bitmap_size);
     if (type() != BS_HEAP_BIG_WRITE)
         return NULL;
-    return ((uint8_t*)this + sizeof(heap_write_t) + 2*heap->dsk->clean_entry_bitmap_size);
+    return ((uint8_t*)this + sizeof(heap_big_write_t) + 2*heap->dsk->clean_entry_bitmap_size);
 }
 
 uint32_t *heap_write_t::get_checksum(blockstore_heap_t *heap)
 {
-    if (heap->dsk->csum_block_size || !len ||
-        type() != BS_HEAP_SMALL_WRITE && type() != BS_HEAP_INTENT_WRITE)
+    if (heap->dsk->csum_block_size ||
+        type() != BS_HEAP_SMALL_WRITE && type() != BS_HEAP_INTENT_WRITE ||
+        small().len == 0)
+    {
         return NULL;
-    return (uint32_t*)((uint8_t*)this + sizeof(heap_write_t) + heap->dsk->clean_entry_bitmap_size);
+    }
+    return (uint32_t*)((uint8_t*)this + sizeof(heap_small_write_t) + heap->dsk->clean_entry_bitmap_size);
 }
 
 heap_write_t *heap_object_t::get_writes()
@@ -164,7 +183,7 @@ blockstore_heap_t::blockstore_heap_t(blockstore_disk_t *dsk, uint8_t *buffer_are
     log_level(log_level),
     meta_block_count(dsk->meta_area_size/dsk->meta_block_size-1), // first block is the superblock
     target_block_free_space(dsk->meta_block_target_free_space),
-    max_write_entry_size(sizeof(heap_write_t) + 2*dsk->clean_entry_bitmap_size +
+    max_write_entry_size(sizeof(heap_small_write_t) + 2*dsk->clean_entry_bitmap_size +
         (dsk->csum_block_size ? dsk->data_block_size/dsk->csum_block_size*(dsk->data_csum_type & 0xFF) : 4 /*sizeof crc32c*/))
 {
     assert(target_block_free_space < dsk->meta_block_size);
@@ -343,13 +362,13 @@ skip_unseen:
                 goto skip_unseen;
             }
             // Verify write chain
-            if (obj->write_pos < -(int16_t)block_offset || obj->write_pos > (int16_t)(dsk->meta_block_size-block_offset-sizeof(heap_write_t)))
+            if (obj->write_pos < -(int16_t)block_offset || obj->write_pos > (int16_t)(dsk->meta_block_size-block_offset-sizeof(heap_small_write_t)))
             {
                 fprintf(stderr, "Warning: Object %jx:%jx in metadata block %u at %u write offset (%d) exceeds block boundaries, skipping object\n",
                     obj->inode, obj->stripe, block_num, block_offset, obj->write_pos);
                 goto skip_corrupted;
             }
-            if (obj->write_pos < 0 && obj->write_pos > -sizeof(heap_write_t) ||
+            if (obj->write_pos < 0 && obj->write_pos > -sizeof(heap_small_write_t) ||
                 obj->write_pos > 0 && obj->write_pos < sizeof(heap_object_t))
             {
                 fprintf(stderr, "Warning: Object %jx:%jx in metadata block %u at %u write offset (%d) intersects the object itself, skipping object\n",
@@ -441,7 +460,7 @@ skip_unseen:
                     continue;
                 }
                 if (wr->type() == BS_HEAP_SMALL_WRITE &&
-                    !is_buffer_area_free(wr->location, wr->len))
+                    !is_buffer_area_free(wr->small().location, wr->small().len))
                 {
                     fprintf(stderr, "Error: write %jx:%jx v%lu (l%lu) buffered data overlaps with other writes, skipping object\n",
                         obj->inode, obj->stripe, wr->version, wr->lsn);
@@ -449,8 +468,7 @@ skip_unseen:
                         abort();
                     goto skip_object;
                 }
-                if (wr->type() == BS_HEAP_BIG_WRITE &&
-                    is_data_used(wr->location))
+                if (wr->type() == BS_HEAP_BIG_WRITE && is_data_used(wr->big().location))
                 {
                     fprintf(stderr, "Error: write %jx:%jx v%lu (l%lu) data overlaps with other writes, skipping object\n",
                         obj->inode, obj->stripe, wr->version, wr->lsn);
@@ -465,7 +483,7 @@ skip_unseen:
                         to_recheck = true;
                     }
                     // recheck small write data immediately
-                    else if (!calc_checksums(wr, buffer_area + wr->location, false))
+                    else if (!calc_checksums(wr, buffer_area + wr->small().location, false))
                     {
                         // entry is invalid (not fully written before OSD crash) - remove it and all newer (previous) entries too
                         if (wr->type() == BS_HEAP_INTENT_WRITE &&
@@ -537,12 +555,12 @@ uint64_t blockstore_heap_t::load_blocks(uint64_t disk_offset, uint64_t size, uin
             used_space += wr->size;
             if (wr->type() == BS_HEAP_SMALL_WRITE)
             {
-                use_buffer_area(obj->inode, wr->location, wr->len);
+                use_buffer_area(obj->inode, wr->small().location, wr->small().len);
             }
             else if (wr->type() == BS_HEAP_BIG_WRITE)
             {
                 // Mark data block as used
-                use_data(obj->inode, wr->location);
+                use_data(obj->inode, wr->big().location);
             }
             if (wr->lsn > this->compacted_lsn)
             {
@@ -618,17 +636,21 @@ void blockstore_heap_t::finish_load()
     tmp_compact_queue.clear();
 }
 
-bool blockstore_heap_t::calc_checksums(heap_write_t *wr, uint8_t *data, bool set)
+bool blockstore_heap_t::calc_checksums(heap_write_t *wr, uint8_t *data, bool set, uint32_t offset, uint32_t len)
 {
     if (!dsk->csum_block_size)
     {
+        if (wr->type() == BS_HEAP_BIG_WRITE)
+        {
+            return true;
+        }
         // Single checksum
         uint32_t *wr_csum = wr->get_checksum(this);
         if (!wr_csum)
         {
             return true;
         }
-        uint32_t real_csum = crc32c(0, data, wr->len);
+        uint32_t real_csum = crc32c(0, data, wr->small().len);
         if (set)
         {
             *wr_csum = real_csum;
@@ -636,10 +658,13 @@ bool blockstore_heap_t::calc_checksums(heap_write_t *wr, uint8_t *data, bool set
         }
         return ((*wr_csum) == real_csum);
     }
-    uint32_t offset = (wr->type() == BS_HEAP_BIG_WRITE
-        ? (wr->offset / dsk->csum_block_size) * (dsk->data_csum_type & 0xFF) : 0);
-    return calc_block_checksums((uint32_t*)(wr->get_checksums(this) + offset), data, wr->get_int_bitmap(this),
-        wr->offset, wr->offset+wr->len, set, NULL);
+    if (wr->type() == BS_HEAP_BIG_WRITE)
+    {
+        return calc_block_checksums((uint32_t*)(wr->get_checksums(this) + offset/dsk->csum_block_size * (dsk->data_csum_type & 0xFF)),
+            data, wr->get_int_bitmap(this), offset, offset+len, set, NULL);
+    }
+    return calc_block_checksums((uint32_t*)wr->get_checksums(this), data, NULL,
+        wr->small().offset, wr->small().offset+wr->small().len, set, NULL);
 }
 
 bool blockstore_heap_t::calc_block_checksums(uint32_t *block_csums, uint8_t *data, uint8_t *bitmap, uint32_t start, uint32_t end,
@@ -751,20 +776,21 @@ bool blockstore_heap_t::recheck_small_writes(std::function<void(bool is_data, ui
             if (wr->needs_recheck(this))
             {
                 bool is_intent = wr->type() == BS_HEAP_INTENT_WRITE;
-                uint64_t loc = wr->location;
+                uint64_t loc = wr->small().location;
                 if (is_intent)
                 {
                     auto next_wr = wr->next();
                     assert(next_wr && next_wr->entry_type == (BS_HEAP_BIG_WRITE | (wr->entry_type & BS_HEAP_STABLE)));
-                    loc = wr->offset + next_wr->location;
+                    loc = wr->small().offset + next_wr->big().location;
                 }
                 recheck_in_progress++;
-                uint8_t *buf = (uint8_t*)memalign_or_die(MEM_ALIGNMENT, wr->len);
+                uint8_t *buf = (uint8_t*)memalign_or_die(MEM_ALIGNMENT, wr->small().len);
                 if (log_level > 5)
                 {
-                    fprintf(stderr, "Notice: rechecking %u bytes at %ju in %s area (lsn %lu)\n", wr->len, loc, is_intent ? "data" : "buffer", wr->lsn);
+                    fprintf(stderr, "Notice: rechecking %u bytes at %ju in %s area (lsn %lu)\n",
+                        wr->small().len, loc, is_intent ? "data" : "buffer", wr->lsn);
                 }
-                recheck_cb(is_intent, loc, wr->len, buf, [this, oid, lsn = wr->lsn, buf]()
+                recheck_cb(is_intent, loc, wr->small().len, buf, [this, oid, lsn = wr->lsn, buf]()
                 {
                     uint32_t block_num = 0;
                     heap_object_t *obj = read_entry(oid, &block_num);
@@ -1053,13 +1079,13 @@ uint32_t blockstore_heap_t::compact_object_to(heap_object_t *obj, uint64_t compa
         if (compacted_wr_count)
         {
             bool is_last = !wr->next();
+            // all subsequent small write entries must also be compacted
+            assert(compacted_wr_count == 1 || wr->is_allowed_before_compacted(compact_lsn, is_last));
             if (wr->type() == BS_HEAP_BIG_WRITE)
             {
                 big_wr = wr;
             }
-            // all subsequent small write entries must also be compacted
-            assert(compacted_wr_count == 1 || wr->is_allowed_before_compacted(compact_lsn, is_last));
-            if (!new_csums && !wr->can_be_collapsed(this))
+            else if (!new_csums && !wr->can_be_collapsed(this))
             {
                 skip_csums = true;
             }
@@ -1080,32 +1106,23 @@ uint32_t blockstore_heap_t::compact_object_to(heap_object_t *obj, uint64_t compa
     // Collapse compacted_wrs[] into big_wr
     big_wr->lsn = compacted_wrs[0]->lsn;
     big_wr->version = compacted_wrs[0]->version;
-    big_wr->len += big_wr->offset;
     memcpy(big_wr->get_ext_bitmap(this), compacted_wrs[0]->get_ext_bitmap(this), dsk->clean_entry_bitmap_size);
-    for (int i = 0; i < compacted_wr_count; i++)
-    {
-        auto cur_wr = compacted_wrs[i];
-        if (big_wr->offset > cur_wr->offset)
-            big_wr->offset = cur_wr->offset;
-        if (big_wr->len < cur_wr->offset+cur_wr->len)
-            big_wr->len = cur_wr->offset+cur_wr->len;
-    }
-    big_wr->len -= big_wr->offset;
     uint8_t *int_bmp = big_wr->get_int_bitmap(this);
     uint8_t *csums = big_wr->get_checksums(this);
     const uint32_t csum_size = (dsk->data_csum_type & 0xFF);
     for (int i = compacted_wr_count-1; i >= 0; i--)
     {
         auto cur_wr = compacted_wrs[i];
-        bitmap_set(int_bmp, cur_wr->offset, cur_wr->len, dsk->bitmap_granularity);
+        assert(cur_wr->type() == BS_HEAP_SMALL_WRITE || cur_wr->type() == BS_HEAP_INTENT_WRITE);
+        bitmap_set(int_bmp, cur_wr->small().offset, cur_wr->small().len, dsk->bitmap_granularity);
         // copy checksums
         if (csums && !skip_csums && !new_csums)
         {
             assert(i == compacted_wr_count-1 ||
-                (cur_wr->offset % dsk->csum_block_size) == 0 &&
-                (cur_wr->len % dsk->csum_block_size) == 0);
-            memcpy(csums + cur_wr->offset/dsk->csum_block_size*csum_size,
-                cur_wr->get_checksums(this), cur_wr->len/dsk->csum_block_size*csum_size);
+                (cur_wr->small().offset % dsk->csum_block_size) == 0 &&
+                (cur_wr->small().len % dsk->csum_block_size) == 0);
+            memcpy(csums + cur_wr->small().offset/dsk->csum_block_size*csum_size,
+                cur_wr->get_checksums(this), cur_wr->small().len/dsk->csum_block_size*csum_size);
         }
     }
     if (csums && new_csums)
@@ -1465,7 +1482,7 @@ bool blockstore_heap_t::mvcc_save_copy(heap_object_t *obj)
     {
         if (wr->type() == BS_HEAP_BIG_WRITE)
         {
-            mvcc_data_refs[wr->location] += add_ref;
+            mvcc_data_refs[wr->big().location] += add_ref;
             if (wr->entry_type & BS_HEAP_STABLE)
             {
                 if (!for_obj)
@@ -1475,9 +1492,9 @@ bool blockstore_heap_t::mvcc_save_copy(heap_object_t *obj)
                 add_ref = 1;
             }
         }
-        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->len > 0)
+        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->small().len > 0)
         {
-            mvcc_buffer_refs[wr->location] += add_ref;
+            mvcc_buffer_refs[wr->small().location] += add_ref;
         }
     }
     // copied :-)
@@ -1494,13 +1511,13 @@ void blockstore_heap_t::mark_overwritten(uint64_t over_lsn, uint64_t inode, heap
         }
         if (wr->type() == BS_HEAP_BIG_WRITE)
         {
-            overwrite_ref_queue.push_back((heap_refqi_t){ .lsn = over_lsn, .inode = inode, .location = wr->location, .len = 0, .is_data = true });
-            mvcc_data_refs[wr->location] += !tracking_active;
+            overwrite_ref_queue.push_back((heap_refqi_t){ .lsn = over_lsn, .inode = inode, .location = wr->big().location, .len = 0, .is_data = true });
+            mvcc_data_refs[wr->big().location] += !tracking_active;
         }
-        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->len > 0)
+        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->small().len > 0)
         {
-            overwrite_ref_queue.push_back((heap_refqi_t){ .lsn = over_lsn, .inode = inode, .location = wr->location, .len = wr->len, .is_data = false });
-            mvcc_buffer_refs[wr->location] += !tracking_active;
+            overwrite_ref_queue.push_back((heap_refqi_t){ .lsn = over_lsn, .inode = inode, .location = wr->small().location, .len = wr->small().len, .is_data = false });
+            mvcc_buffer_refs[wr->small().location] += !tracking_active;
         }
         wr = wr->next();
     }
@@ -1592,11 +1609,11 @@ int blockstore_heap_t::update_object(uint32_t block_num, heap_object_t *obj, hea
         // MVCC reference tracking is in action for the object, increase the refcount
         if (wr->type() == BS_HEAP_BIG_WRITE)
         {
-            mvcc_data_refs[wr->location]++;
+            mvcc_data_refs[wr->big().location]++;
         }
-        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->len > 0)
+        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->small().len > 0)
         {
-            mvcc_buffer_refs[wr->location]++;
+            mvcc_buffer_refs[wr->small().location]++;
         }
     }
     const uint8_t *old_data = inf->data;
@@ -1623,16 +1640,16 @@ int blockstore_heap_t::update_object(uint32_t block_num, heap_object_t *obj, hea
         first_wr->can_be_collapsed(this))
     {
         auto second_wr = first_wr->next();
+        assert(second_wr->type() == BS_HEAP_BIG_WRITE);
+        auto first_offset = first_wr->small().offset;
+        auto first_len = first_wr->small().len;
         second_wr->version = first_wr->version;
-        second_wr->len = (first_wr->offset+first_wr->len > second_wr->offset+second_wr->len ? first_wr->offset+first_wr->len : second_wr->offset+second_wr->len);
-        second_wr->offset = first_wr->offset < second_wr->offset ? first_wr->offset : second_wr->offset;
-        second_wr->len -= second_wr->offset;
-        bitmap_set(second_wr->get_int_bitmap(this), first_wr->offset, first_wr->len, dsk->bitmap_granularity);
+        bitmap_set(second_wr->get_int_bitmap(this), first_offset, first_len, dsk->bitmap_granularity);
         if (dsk->csum_block_size)
         {
             const uint32_t csum_size = (dsk->data_csum_type & 0xFF);
-            memcpy(second_wr->get_checksums(this) + first_wr->offset/dsk->csum_block_size*csum_size,
-                first_wr->get_checksums(this), first_wr->len/dsk->csum_block_size*csum_size);
+            memcpy(second_wr->get_checksums(this) + first_offset/dsk->csum_block_size*csum_size,
+                first_wr->get_checksums(this), first_len/dsk->csum_block_size*csum_size);
         }
         used_delta -= free_writes(first_wr, second_wr);
         new_wr->next_pos = (uint8_t*)second_wr - (uint8_t*)new_wr;
@@ -1957,16 +1974,16 @@ void blockstore_heap_t::free_object_space(inode_t inode, heap_write_t *from, hea
     {
         if (wr->type() == BS_HEAP_BIG_WRITE)
         {
-            deref_data(inode, wr->location, mode != BS_HEAP_FREE_MAIN);
+            deref_data(inode, wr->big().location, mode != BS_HEAP_FREE_MAIN);
             if (mode == BS_HEAP_FREE_MVCC && (wr->entry_type & BS_HEAP_STABLE))
             {
                 // Stop at the last visible version
                 break;
             }
         }
-        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->len > 0)
+        else if (wr->type() == BS_HEAP_SMALL_WRITE && wr->small().len > 0)
         {
-            deref_buffer(inode, wr->location, wr->len, mode != BS_HEAP_FREE_MAIN);
+            deref_buffer(inode, wr->small().location, wr->small().len, mode != BS_HEAP_FREE_MAIN);
         }
     }
 }
@@ -2010,7 +2027,7 @@ void blockstore_heap_t::add_used_space(uint32_t block_num, int32_t used_delta)
 {
     auto & inf = block_info.at(block_num);
     meta_used_space += used_delta;
-    auto thresh = dsk->meta_block_size-target_block_free_space;
+    auto thresh = (dsk->meta_block_size-target_block_free_space) - (dsk->meta_block_size-target_block_free_space)%MIN_ALLOC;
     auto old_used_space = inf.used_space;
     inf.used_space += used_delta;
     meta_alloc->change(block_num,
diff --git a/src/blockstore/blockstore_heap.h b/src/blockstore/blockstore_heap.h
index 7b35d78b..3fcdd95a 100644
--- a/src/blockstore/blockstore_heap.h
+++ b/src/blockstore/blockstore_heap.h
@@ -31,6 +31,37 @@ struct pool_shard_settings_t
 
 class blockstore_heap_t;
 
+struct __attribute__((__packed__)) heap_small_write_t
+{
+    uint16_t size;
+    int16_t next_pos;
+    uint8_t flags;
+    uint64_t lsn;
+    uint64_t version;
+    uint64_t location;
+    uint32_t offset;
+    uint32_t len;
+};
+
+struct __attribute__((__packed__)) heap_big_write_t
+{
+    uint16_t size;
+    int16_t next_pos;
+    uint8_t flags;
+    uint64_t lsn;
+    uint64_t version;
+    uint64_t location;
+};
+
+struct __attribute__((__packed__)) heap_tombstone_t
+{
+    uint16_t size;
+    int16_t next_pos;
+    uint8_t flags;
+    uint64_t lsn;
+    uint64_t version;
+};
+
 struct __attribute__((__packed__)) heap_write_t
 {
     // size should have top bit cleared
@@ -39,9 +70,6 @@ struct __attribute__((__packed__)) heap_write_t
     uint8_t entry_type = 0; // BS_HEAP_*
     uint64_t lsn = 0;
     uint64_t version = 0;
-    uint32_t offset = 0;
-    uint32_t len = 0;
-    uint64_t location = 0;
 
     // uint8_t[] external_bitmap
     // uint8_t[] internal_bitmap
@@ -49,6 +77,8 @@ struct __attribute__((__packed__)) heap_write_t
 
     heap_write_t *next();
     inline uint8_t type() const { return (entry_type & BS_HEAP_TYPE); }
+    inline heap_small_write_t& small() { return *(heap_small_write_t*)this; }
+    inline heap_big_write_t& big() { return *(heap_big_write_t*)this; }
     uint32_t get_size(blockstore_heap_t *heap);
     uint32_t get_csum_size(blockstore_heap_t *heap);
     bool needs_recheck(blockstore_heap_t *heap);
@@ -262,7 +292,7 @@ public:
     // unlock an entry
     bool unlock_entry(object_id oid, uint64_t copy_id);
     // set or verify checksums in a write request
-    bool calc_checksums(heap_write_t *wr, uint8_t *data, bool set);
+    bool calc_checksums(heap_write_t *wr, uint8_t *data, bool set, uint32_t offset = 0, uint32_t len = 0);
     // set or verify raw block checksums
     bool calc_block_checksums(uint32_t *block_csums, uint8_t *data, uint8_t *bitmap, uint32_t start, uint32_t end,
         bool set, std::function<void(uint32_t, uint32_t, uint32_t)> bad_block_cb);
diff --git a/src/blockstore/blockstore_read.cpp b/src/blockstore/blockstore_read.cpp
index a6533563..113c0eaf 100644
--- a/src/blockstore/blockstore_read.cpp
+++ b/src/blockstore/blockstore_read.cpp
@@ -169,12 +169,13 @@ uint32_t blockstore_impl_t::prepare_read_zero(std::vector<copy_buffer_t> & read_
 uint32_t blockstore_impl_t::prepare_read_simple(std::vector<copy_buffer_t> & read_vec, heap_object_t *obj, heap_write_t *wr, uint32_t start, uint32_t end)
 {
     uint32_t res = 0;
-    if (wr->offset >= end || wr->offset+wr->len <= start)
+    if (wr->type() == BS_HEAP_SMALL_WRITE || wr->type() == BS_HEAP_INTENT_WRITE)
     {
-        return 0;
+        if (wr->small().offset >= end || wr->small().offset+wr->small().len <= start)
+            return 0;
+        start = start < wr->small().offset ? wr->small().offset : start;
+        end = end > wr->small().offset+wr->small().len ? wr->small().offset+wr->small().len : end;
     }
-    start = start < wr->offset ? wr->offset : start;
-    end = end > wr->offset+wr->len ? wr->offset+wr->len : end;
     find_holes(read_vec, start, end, [&](int & pos, uint32_t start, uint32_t end)
     {
         res += end-start;
@@ -185,10 +186,10 @@ uint32_t blockstore_impl_t::prepare_read_simple(std::vector<copy_buffer_t> & rea
                 .copy_flags = COPY_BUF_JOURNAL | COPY_BUF_SKIP_CSUM,
                 .offset = start,
                 .len = end-start,
-                .disk_loc = wr->location - wr->offset,
+                .disk_loc = wr->small().location - wr->small().offset,
                 .disk_offset = start,
                 .disk_len = end-start,
-                .buf = buffer_area + wr->location + start - wr->offset,
+                .buf = buffer_area + wr->small().location + start - wr->small().offset,
                 .wr_lsn = wr->lsn,
             });
         }
@@ -202,14 +203,18 @@ uint32_t blockstore_impl_t::prepare_read_simple(std::vector<copy_buffer_t> & rea
             // the most complex case: read data from disk with padding
             uint32_t blk_start = start, blk_end = end;
             blk_start = (start/dsk.csum_block_size) * dsk.csum_block_size;
-            blk_start = blk_start < wr->offset ? wr->offset : blk_start;
             blk_end = ((end-1) / dsk.csum_block_size + 1) * dsk.csum_block_size;
-            blk_end = blk_end > wr->offset+wr->len ? wr->offset+wr->len : blk_end;
+            if (wr->type() == BS_HEAP_INTENT_WRITE || wr->type() == BS_HEAP_SMALL_WRITE)
+            {
+                blk_start = blk_start < wr->small().offset ? wr->small().offset : blk_start;
+                blk_end = blk_end > wr->small().offset+wr->small().len ? wr->small().offset+wr->small().len : blk_end;
+            }
             uint32_t skip_csum = 0;
             if (!perfect_csum_update && wr->type() == BS_HEAP_BIG_WRITE)
             {
                 for (auto owr = obj->get_writes(); owr && owr != wr; owr = owr->next())
-                    if (owr->offset < blk_end && owr->offset+owr->len > blk_start)
+                    if ((owr->type() == BS_HEAP_INTENT_WRITE || owr->type() == BS_HEAP_SMALL_WRITE) &&
+                        owr->small().offset < blk_end && owr->small().offset+owr->small().len > blk_start)
                         skip_csum = COPY_BUF_SKIP_CSUM;
             }
             if ((blk_end-1)/dsk.csum_block_size == blk_start/dsk.csum_block_size ||
@@ -247,7 +252,9 @@ void blockstore_impl_t::prepare_disk_read(std::vector<copy_buffer_t> & read_vec,
         .copy_flags = (wr->type() == BS_HEAP_SMALL_WRITE ? COPY_BUF_JOURNAL : COPY_BUF_DATA) | copy_flags,
         .offset = start,
         .len = end-start,
-        .disk_loc = (wr->type() == BS_HEAP_INTENT_WRITE ? wr->next()->location : wr->location - (wr->type() == BS_HEAP_SMALL_WRITE ? wr->offset : 0)),
+        .disk_loc = (wr->type() == BS_HEAP_INTENT_WRITE ? wr->next()->big().location
+            : (wr->type() == BS_HEAP_SMALL_WRITE ? wr->small().location-wr->small().offset
+            : wr->big().location)),
         .disk_offset = blk_start,
         .disk_len = blk_end - blk_start,
         .wr_lsn = wr->lsn,
@@ -367,7 +374,7 @@ bool blockstore_impl_t::verify_read_checksums(blockstore_op_t *op)
         uint8_t *buf = vec.buf ? vec.buf : (op->buf + vec.offset - op->offset);
         uint32_t *csums = (uint32_t*)(wr->get_checksums(heap)
             + (vec.disk_offset/dsk.csum_block_size)*(dsk.data_csum_type & 0xFF)
-            - ((wr->type() == BS_HEAP_BIG_WRITE) ? 0 : (wr->offset/dsk.csum_block_size)*(dsk.data_csum_type & 0xFF)));
+            - ((wr->type() == BS_HEAP_BIG_WRITE) ? 0 : (wr->small().offset/dsk.csum_block_size)*(dsk.data_csum_type & 0xFF)));
         if (!heap->calc_block_checksums(csums, buf, wr->get_int_bitmap(heap),
             vec.disk_offset, vec.disk_offset+vec.disk_len, false, [&](uint32_t mismatch_pos, uint32_t expected_csum, uint32_t real_csum)
             {
diff --git a/src/blockstore/blockstore_write.cpp b/src/blockstore/blockstore_write.cpp
index a50cd96e..492b4505 100644
--- a/src/blockstore/blockstore_write.cpp
+++ b/src/blockstore/blockstore_write.cpp
@@ -149,21 +149,21 @@ int blockstore_impl_t::dequeue_write(blockstore_op_t *op)
         BS_SUBMIT_CHECK_SQES(1);
         if (obj->get_writes()->type() == BS_HEAP_BIG_WRITE)
         {
-            PRIV(op)->location = obj->get_writes()->location;
+            PRIV(op)->location = obj->get_writes()->big().location;
         }
         else
         {
             assert(obj->get_writes()->next()->type() == BS_HEAP_BIG_WRITE);
-            PRIV(op)->location = obj->get_writes()->next()->location;
+            PRIV(op)->location = obj->get_writes()->next()->big().location;
         }
 process_intent:
         uint8_t wr_buf[heap->get_max_write_entry_size()];
         heap_write_t *wr = (heap_write_t*)wr_buf;
         wr->version = op->version;
-        wr->offset = op->offset;
-        wr->len = op->len;
-        wr->location = 0;
         wr->entry_type = BS_HEAP_INTENT_WRITE | (op->opcode == BS_OP_WRITE_STABLE ? BS_HEAP_STABLE : 0);
+        wr->small().offset = op->offset;
+        wr->small().len = op->len;
+        wr->small().location = 0;
         if (op->bitmap)
             memcpy(wr->get_ext_bitmap(heap), op->bitmap, dsk.clean_entry_bitmap_size);
         heap->calc_checksums(wr, (uint8_t*)op->buf, true);
@@ -208,11 +208,11 @@ process_intent:
         uint8_t wr_buf[heap->get_max_write_entry_size()];
         heap_write_t *wr = (heap_write_t*)wr_buf;
         wr->version = op->version;
-        wr->offset = op->offset;
-        wr->len = op->len;
-        wr->location = loc;
-        PRIV(op)->location = loc;
         wr->entry_type = BS_HEAP_SMALL_WRITE | (op->opcode == BS_OP_WRITE_STABLE ? BS_HEAP_STABLE : 0);
+        wr->small().offset = op->offset;
+        wr->small().len = op->len;
+        wr->small().location = loc;
+        PRIV(op)->location = loc;
         if (op->bitmap)
             memcpy(wr->get_ext_bitmap(heap), op->bitmap, dsk.clean_entry_bitmap_size);
         heap->calc_checksums(wr, (uint8_t*)op->buf, true);
@@ -267,16 +267,14 @@ int blockstore_impl_t::make_big_write(blockstore_op_t *op, uint32_t offset, uint
 {
     uint8_t wr_buf[heap->get_max_write_entry_size()];
     heap_write_t *wr = (heap_write_t*)wr_buf;
-    wr->version = op->version;
-    wr->offset = offset;
-    wr->len = len;
-    wr->location = PRIV(op)->location;
     wr->entry_type = BS_HEAP_BIG_WRITE | (op->opcode == BS_OP_WRITE_STABLE ? BS_HEAP_STABLE : 0);
+    wr->version = op->version;
+    wr->big().location = PRIV(op)->location;
     if (op->bitmap)
         memcpy(wr->get_ext_bitmap(heap), op->bitmap, dsk.clean_entry_bitmap_size);
     memset(wr->get_int_bitmap(heap), 0, dsk.clean_entry_bitmap_size);
     bitmap_set(wr->get_int_bitmap(heap), offset, len, dsk.bitmap_granularity);
-    heap->calc_checksums(wr, (uint8_t*)op->buf, true);
+    heap->calc_checksums(wr, (uint8_t*)op->buf, true, offset, len);
     int res = heap->post_write(op->oid, wr, modified_block, moved_from_block);
     if (res != 0)
         return res;
diff --git a/src/disk_tool/disk_tool_discard.cpp b/src/disk_tool/disk_tool_discard.cpp
index 82ca7dd6..1b68c9bf 100644
--- a/src/disk_tool/disk_tool_discard.cpp
+++ b/src/disk_tool/disk_tool_discard.cpp
@@ -61,7 +61,7 @@ int disk_tool_t::trim_data(std::string device)
             {
                 if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE)
                 {
-                    data_alloc->set(wr->location / dsk.data_block_size, true);
+                    data_alloc->set(wr->big().location / dsk.data_block_size, true);
                 }
             }
         },
diff --git a/src/disk_tool/disk_tool_meta.cpp b/src/disk_tool/disk_tool_meta.cpp
index 4b9ceab4..b8059907 100644
--- a/src/disk_tool/disk_tool_meta.cpp
+++ b/src/disk_tool/disk_tool_meta.cpp
@@ -349,7 +349,7 @@ void disk_tool_t::dump_heap_entry_as_old(blockstore_heap_t *heap, heap_object_t
 #define ENTRY_FMT "{\"block\":%ju,\"pool\":%u,\"inode\":\"0x%jx\",\"stripe\":\"0x%jx\",\"version\":%ju"
         (first_entry ? ENTRY_FMT : (",\n" ENTRY_FMT)),
 #undef ENTRY_FMT
-        wr->location/dsk.data_block_size, INODE_POOL(obj->inode), INODE_NO_POOL(obj->inode),
+        wr->big().location/dsk.data_block_size, INODE_POOL(obj->inode), INODE_NO_POOL(obj->inode),
         obj->stripe, wr->version
     );
     printf(",\"bitmap\":\"");
@@ -395,27 +395,36 @@ void disk_tool_t::dump_heap_entry(blockstore_heap_t *heap, heap_object_t *obj)
     for (wr = obj->get_writes(); wr; wr = wr->next())
     {
         printf(
-#define ENTRY_FMT "{\"lsn\":%ju,\"version\":%ju,\"type\":\"%s\",\"stable\":%s,\"offset\":%u,\"len\":%u"
+#define ENTRY_FMT "{\"lsn\":%ju,\"version\":%ju,\"type\":\"%s\",\"stable\":%s"
             (first_wr ? ENTRY_FMT : ("," ENTRY_FMT)),
 #undef ENTRY_FMT
             wr->lsn, wr->version, (wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE ? "small" : (
                 (wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE ? "big" : (
                 (wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_INTENT_WRITE ? "intent" : (
                 (wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_TOMBSTONE ? "tombstone" : "unknown"))),
-            (wr->entry_type & BS_HEAP_STABLE) ? "true" : "false",
-            wr->offset, wr->len
+            (wr->entry_type & BS_HEAP_STABLE) ? "true" : "false"
         );
-        if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE ||
-            (wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE && !dump_with_data)
+        if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE)
         {
-            printf(",\"location\":%ju", wr->location);
+            printf(",\"location\":%ju", wr->big().location);
         }
-        else if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE && dump_with_data)
+        else if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_INTENT_WRITE)
         {
-            printf(",\"data\":\"");
-            for (uint32_t i = 0; i < wr->len; i++)
-                printf("%02x", buffer_area[wr->location + i]);
-            printf("\"");
+            printf(",\"offset\":%u,\"len\":%u", wr->small().offset, wr->small().len);
+        }
+        else if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE)
+        {
+            if (!dump_with_data)
+            {
+                printf(",\"offset\":%u,\"len\":%u,\"location\":%ju", wr->small().offset, wr->small().len, wr->small().location);
+            }
+            else
+            {
+                printf(",\"data\":\"");
+                for (uint32_t i = 0; i < wr->small().len; i++)
+                    printf("%02x", buffer_area[wr->small().location + i]);
+                printf("\"");
+            }
         }
         uint8_t* bitmap = wr->get_int_bitmap(heap);
         if (bitmap)
@@ -640,21 +649,28 @@ int disk_tool_t::write_json_heap(json11::Json meta, json11::Json journal)
                 wr->entry_type = wr_type | (write_entry["stable"].bool_value() ? BS_HEAP_STABLE : 0);
                 wr->lsn = write_entry["lsn"].uint64_value();
                 wr->version = write_entry["version"].uint64_value();
-                wr->offset = write_entry["offset"].uint64_value();
-                wr->len = write_entry["len"].uint64_value();
-                wr->location = write_entry["location"].uint64_value();
                 wr->size = wr->get_size(new_heap);
                 wr->next_pos = wr->size;
-                if (wr_type == BS_HEAP_SMALL_WRITE && write_entry["data"].is_string() && wr->len > 0)
+                if (wr_type == BS_HEAP_SMALL_WRITE || wr_type == BS_HEAP_INTENT_WRITE)
                 {
-                    if (!new_journal_buf)
+                    wr->small().offset = write_entry["offset"].uint64_value();
+                    wr->small().len = write_entry["len"].uint64_value();
+                    wr->small().location = write_entry["location"].uint64_value();
+                    if (wr_type == BS_HEAP_SMALL_WRITE && write_entry["data"].is_string() && wr->small().len > 0)
                     {
-                        fprintf(stderr, "Loading small write data requires overwriting buffer area\n");
-                        free_new_meta();
-                        return 1;
+                        if (!new_journal_buf)
+                        {
+                            fprintf(stderr, "Loading small write data requires overwriting buffer area\n");
+                            free_new_meta();
+                            return 1;
+                        }
+                        wr->small().location = new_heap->find_free_buffer_area(wr->small().len);
+                        fromhexstr(write_entry["data"].string_value(), wr->small().len, new_journal_buf + wr->small().location);
                     }
-                    wr->location = new_heap->find_free_buffer_area(wr->len);
-                    fromhexstr(write_entry["data"].string_value(), wr->len, new_journal_buf + wr->location);
+                }
+                else if (wr_type == BS_HEAP_BIG_WRITE)
+                {
+                    wr->big().location = write_entry["location"].uint64_value();
                 }
                 if (write_entry["bitmap"].is_string() && wr->get_int_bitmap(new_heap))
                 {
@@ -778,9 +794,7 @@ close_err:
             wr->entry_type = BS_HEAP_BIG_WRITE|BS_HEAP_STABLE;
             wr->lsn = ++next_lsn;
             wr->version = sscanf_json(NULL, meta_entry["version"]);
-            wr->offset = 0;
-            wr->len = new_meta_hdr->data_block_size;
-            wr->location = meta_entry["block"].uint64_value() * new_meta_hdr->data_block_size;
+            wr->big().location = meta_entry["block"].uint64_value() * new_meta_hdr->data_block_size;
             wr->size = wr->get_size(&heap);
             fromhexstr(meta_entry["bitmap"].string_value(), new_clean_entry_bitmap_size, wr->get_int_bitmap(&heap));
             fromhexstr(meta_entry["ext_bitmap"].string_value(), new_clean_entry_bitmap_size, wr->get_ext_bitmap(&heap));
@@ -795,36 +809,39 @@ close_err:
                     wr->next_pos = 0;
                     wr->lsn = ++next_lsn;
                     wr->version = rec["ver"].uint64_value();
-                    wr->offset = rec["offset"].uint64_value();
-                    wr->len = rec["len"].uint64_value();
+                    uint64_t wr_offset = rec["offset"].uint64_value();
+                    uint64_t wr_len = rec["len"].uint64_value();
                     if (rec["type"] == "small_write" || rec["type"] == "small_write_instant")
                     {
-                        if (wr->len > 0 && !rec["data"].is_string())
+                        if (wr_len > 0 && !rec["data"].is_string())
                         {
                             fprintf(stderr, "Error: entry data is missing, please generate the dump with --json --format data\n");
                             goto close_err;
                         }
                         wr->entry_type = BS_HEAP_SMALL_WRITE | (rec["type"] == "small_write_instant" ? BS_HEAP_STABLE : 0);
+                        wr->small().offset = wr_offset;
+                        wr->small().len = wr_len;
+                        wr->small().location = buffer_pos;
                         fromhexstr(rec["bitmap"].string_value(), new_clean_entry_bitmap_size, wr->get_ext_bitmap(&heap));
-                        fromhexstr(rec["data"].string_value(), wr->len, new_journal_buf+buffer_pos);
-                        if (wr->len > 0)
+                        fromhexstr(rec["data"].string_value(), wr_len, new_journal_buf+buffer_pos);
+                        if (wr_len > 0)
                         {
                             if (!new_meta_hdr->data_csum_type)
-                                *wr->get_checksum(&heap) = crc32c(0, new_journal_buf+buffer_pos, wr->len);
+                                *wr->get_checksum(&heap) = crc32c(0, new_journal_buf+buffer_pos, wr_len);
                             else
-                                heap.calc_block_checksums((uint32_t*)wr->get_checksums(&heap), new_journal_buf+buffer_pos, NULL, wr->offset, wr->offset+wr->len, true, NULL);
+                                heap.calc_block_checksums((uint32_t*)wr->get_checksums(&heap), new_journal_buf+buffer_pos, NULL, wr_offset, wr_offset+wr_len, true, NULL);
                         }
-                        buffer_pos += wr->len;
+                        buffer_pos += wr_len;
                     }
                     else if (rec["type"] == "big_write" || rec["type"] == "big_write_instant")
                     {
                         wr->entry_type = BS_HEAP_BIG_WRITE | (rec["type"] == "big_write_instant" ? BS_HEAP_STABLE : 0);
-                        wr->location = sscanf_json(NULL, rec["loc"]);
-                        bitmap_set(wr->get_int_bitmap(&heap), wr->offset, wr->len, new_meta_hdr->bitmap_granularity);
+                        wr->big().location = sscanf_json(NULL, rec["loc"]);
+                        bitmap_set(wr->get_int_bitmap(&heap), wr_offset, wr_len, new_meta_hdr->bitmap_granularity);
                         fromhexstr(rec["bitmap"].string_value(), new_clean_entry_bitmap_size, wr->get_ext_bitmap(&heap));
                         if (new_meta_hdr->data_csum_type != 0)
                         {
-                            if ((wr->offset % new_meta_hdr->csum_block_size) || (wr->len % new_meta_hdr->csum_block_size))
+                            if ((wr_offset % new_meta_hdr->csum_block_size) || (wr_len % new_meta_hdr->csum_block_size))
                             {
                                 fprintf(stderr,
                                     "Error: big_write journal entries not aligned to csum_block_size can't be converted between v0.9 and v3.0 metadata\n"
@@ -832,8 +849,8 @@ close_err:
                                 goto close_err;
                             }
                             fromhexstr(rec["block_csums"].string_value(),
-                                ((wr->offset+wr->len+new_meta_hdr->csum_block_size-1)/new_meta_hdr->csum_block_size
-                                    - wr->offset/new_meta_hdr->csum_block_size) * (new_meta_hdr->data_csum_type & 0xFF),
+                                ((wr_offset+wr_len+new_meta_hdr->csum_block_size-1)/new_meta_hdr->csum_block_size
+                                    - wr_offset/new_meta_hdr->csum_block_size) * (new_meta_hdr->data_csum_type & 0xFF),
                                 wr->get_checksums(&heap));
                         }
                     }
diff --git a/src/disk_tool/disk_tool_resize.cpp b/src/disk_tool/disk_tool_resize.cpp
index e1d6fc35..f3bc09b9 100644
--- a/src/disk_tool/disk_tool_resize.cpp
+++ b/src/disk_tool/disk_tool_resize.cpp
@@ -43,7 +43,7 @@ int disk_tool_t::raw_resize()
             {
                 if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE)
                 {
-                    data_alloc->set(wr->location / dsk.data_block_size, true);
+                    data_alloc->set(wr->big().location / dsk.data_block_size, true);
                 }
             }
         },
@@ -569,13 +569,7 @@ int disk_tool_t::resize_rebuild_meta()
             {
                 if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE)
                 {
-                    if (wr->next() && new_meta_hdr->data_csum_type != 0 &&
-                        ((wr->offset % new_meta_hdr->csum_block_size) || (wr->len % new_meta_hdr->csum_block_size)))
-                    {
-                        fprintf(stderr, "Error: big_write journal entries not aligned to csum_block_size can't be converted between v0.9 and v3.0 metadata\n");
-                        exit(1);
-                    }
-                    auto block_num = wr->location / dsk.data_block_size;
+                    auto block_num = wr->big().location / dsk.data_block_size;
                     auto remap_it = data_remap.find(block_num);
                     if (remap_it != data_remap.end())
                         block_num = remap_it->second;
@@ -585,20 +579,20 @@ int disk_tool_t::resize_rebuild_meta()
                         exit(1);
                     }
                     block_num += data_idx_diff;
-                    wr->location = block_num * dsk.data_block_size;
+                    wr->big().location = block_num * dsk.data_block_size;
                 }
                 else if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE)
                 {
-                    if (new_heap && wr->len > 0)
+                    if (new_heap && wr->small().len > 0)
                     {
-                        if (new_journal_ptr-new_journal_buf+wr->len > new_journal_len)
+                        if (new_journal_ptr-new_journal_buf+wr->small().len > new_journal_len)
                         {
                             fprintf(stderr, "Small write data doesn't fit into the new buffer area\n");
                             exit(1);
                         }
-                        memcpy(new_journal_ptr, buffer_area+wr->location, wr->len);
-                        wr->location = new_journal_ptr-new_journal_buf;
-                        new_journal_ptr += wr->len;
+                        memcpy(new_journal_ptr, buffer_area+wr->small().location, wr->small().len);
+                        wr->small().location = new_journal_ptr-new_journal_buf;
+                        new_journal_ptr += wr->small().len;
                     }
                 }
                 else if (!new_heap)
@@ -626,8 +620,9 @@ int disk_tool_t::resize_rebuild_meta()
                 {
                     auto wr = writes[i];
                     assert((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE || wr->entry_type == BS_HEAP_BIG_WRITE);
-                    uint32_t je_size = dsk.dirty_dyn_size(wr->offset, wr->len) +
-                        ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE ? sizeof(journal_entry_small_write) : sizeof(journal_entry_big_write));
+                    uint32_t je_size = ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE
+                        ? sizeof(journal_entry_small_write) + dsk.dirty_dyn_size(wr->small().offset, wr->small().len)
+                        : sizeof(journal_entry_big_write) + dsk.dirty_dyn_size(0, dsk.data_block_size));
                     choose_journal_block(je_size);
                     journal_entry *je = (journal_entry*)(new_journal_ptr + new_journal_in_pos);
                     je->magic = JOURNAL_MAGIC;
@@ -636,28 +631,30 @@ int disk_tool_t::resize_rebuild_meta()
                     je->crc32_prev = new_crc32_prev;
                     je->small_write.oid = (object_id){ .inode = obj->inode, .stripe = obj->stripe };
                     je->small_write.version = wr->version;
-                    je->small_write.offset = wr->offset;
-                    je->small_write.len = wr->len;
-                    if ((wr->entry_type & BS_HEAP_TYPE) == BS_HEAP_SMALL_WRITE)
+                    if (wr->type() == BS_HEAP_SMALL_WRITE)
                     {
+                        je->small_write.offset = wr->small().offset;
+                        je->small_write.len = wr->small().len;
                         je->small_write.data_offset = new_journal_data-new_journal_buf;
                         if (je->small_write.data_offset + je->small_write.len > new_journal_len)
                         {
                             fprintf(stderr, "Error: live entries don't fit to the new journal\n");
                             exit(1);
                         }
-                        memcpy(new_journal_data, buffer_area+wr->location, je->small_write.len);
+                        memcpy(new_journal_data, buffer_area+wr->small().location, je->small_write.len);
                         new_journal_data += je->small_write.len;
                         if (dsk.data_csum_type == 0 && wr->get_checksum(heap))
                             je->small_write.crc32_data = *wr->get_checksum(heap);
                     }
                     else
                     {
-                        je->big_write.location = wr->location;
+                        je->big_write.location = wr->big().location;
                     }
                     memcpy((uint8_t*)je + je->size, wr->get_ext_bitmap(heap), new_clean_entry_bitmap_size);
                     if (dsk.data_csum_type != 0 && wr->get_checksums(heap))
-                        memcpy((uint8_t*)je + je->size + new_clean_entry_bitmap_size, wr->get_checksums(heap), new_data_csum_size);
+                    {
+                        memcpy((uint8_t*)je + je->size + new_clean_entry_bitmap_size, wr->get_checksums(heap), wr->get_csum_size(heap));
+                    }
                     je->crc32 = je_crc32(je);
                     new_journal_in_pos += je->size;
                     new_crc32_prev = je->crc32;
@@ -666,7 +663,7 @@ int disk_tool_t::resize_rebuild_meta()
                 if (writes[writes.size()-1]->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE)
                 {
                     auto big_wr = writes[writes.size()-1];
-                    uint64_t block_num = big_wr->location / dsk.data_block_size;
+                    uint64_t block_num = big_wr->big().location / dsk.data_block_size;
                     clean_disk_entry *new_entry = (clean_disk_entry*)(new_meta_buf + dsk.meta_block_size +
                         dsk.meta_block_size*(block_num / new_entries_per_block) +
                         new_clean_entry_size*(block_num % new_entries_per_block));
@@ -697,10 +694,8 @@ int disk_tool_t::resize_rebuild_meta()
                 uint8_t wr_buf[new_heap->get_max_write_entry_size()];
                 heap_write_t *wr = (heap_write_t*)wr_buf;
                 wr->entry_type = BS_HEAP_BIG_WRITE|BS_HEAP_STABLE;
-                wr->location = block_num * dsk.data_block_size;
+                wr->big().location = block_num * dsk.data_block_size;
                 wr->next_pos = 0;
-                wr->offset = 0;
-                wr->len = 0;
                 wr->size = wr->get_size(new_heap);
                 if (bitmap)
                 {
diff --git a/src/test/test_blockstore.cpp b/src/test/test_blockstore.cpp
index 457662cd..ef4836bb 100644
--- a/src/test/test_blockstore.cpp
+++ b/src/test/test_blockstore.cpp
@@ -398,6 +398,8 @@ static void test_padded_csum_intent(bool perfect)
     // (intent is not collapsible because of csum_block_size > bitmap_granularity)
     heap_object_t *obj = test.bs->heap->read_entry((object_id){ .inode = 1, .stripe = 0 }, NULL);
     assert(obj);
+    assert(obj->get_writes()->next());
+    assert(obj->get_writes()->next()->next());
     assert(!obj->get_writes()->next()->next()->next());
     assert(obj->get_writes()->entry_type == BS_HEAP_SMALL_WRITE);
     assert(obj->get_writes()->next()->entry_type == (perfect ? BS_HEAP_SMALL_WRITE : BS_HEAP_INTENT_WRITE));
diff --git a/src/test/test_heap.cpp b/src/test/test_heap.cpp
index 71a5bf9f..bc013a8a 100644
--- a/src/test/test_heap.cpp
+++ b/src/test/test_heap.cpp
@@ -67,12 +67,10 @@ int _test_do_big_write(blockstore_heap_t & heap, blockstore_disk_t & dsk, uint64
     uint8_t wr_buf[heap.get_max_write_entry_size()];
     heap_write_t *wr = (heap_write_t*)wr_buf;
     wr->version = version;
-    wr->offset = offset;
-    wr->len = len;
-    wr->location = location;
+    wr->big().location = location;
     wr->entry_type = BS_HEAP_BIG_WRITE | (stable ? BS_HEAP_STABLE : 0);
     assert(heap.get_max_write_entry_size() >= wr->get_size(&heap));
-    assert(wr->get_size(&heap) == sizeof(heap_write_t) + 2*dsk.clean_entry_bitmap_size + (dsk.csum_block_size
+    assert(wr->get_size(&heap) == sizeof(heap_big_write_t) + 2*dsk.clean_entry_bitmap_size + (dsk.csum_block_size
         ? dsk.data_block_size/dsk.csum_block_size*4 : 0));
     memset(wr->get_ext_bitmap(&heap), 0xff, dsk.clean_entry_bitmap_size);
     memset(wr->get_int_bitmap(&heap), 0, dsk.clean_entry_bitmap_size);
@@ -105,11 +103,11 @@ int _test_do_small_write(blockstore_heap_t & heap, blockstore_disk_t & dsk, uint
     uint8_t wr_buf[heap.get_max_write_entry_size()];
     heap_write_t *wr = (heap_write_t*)wr_buf;
     wr->version = version;
-    wr->offset = offset;
-    wr->len = len;
-    wr->location = location;
+    wr->small().offset = offset;
+    wr->small().len = len;
+    wr->small().location = location;
     wr->entry_type = (is_intent ? BS_HEAP_INTENT_WRITE : BS_HEAP_SMALL_WRITE) | (stable ? BS_HEAP_STABLE : 0);
-    assert(wr->get_size(&heap) == sizeof(heap_write_t) + dsk.clean_entry_bitmap_size + (dsk.csum_block_size
+    assert(wr->get_size(&heap) == sizeof(heap_small_write_t) + dsk.clean_entry_bitmap_size + (dsk.csum_block_size
         ? ((offset+len+dsk.csum_block_size-1)/dsk.csum_block_size - offset/dsk.csum_block_size)*4 : 4));
     memset(wr->get_ext_bitmap(&heap), 0xff, dsk.clean_entry_bitmap_size);
     assert(!wr->get_int_bitmap(&heap));
@@ -173,7 +171,7 @@ void test_mvcc(bool csum)
         assert(heap.find_free_data() == 0);
 
         _test_big_write(heap, dsk, 1, 0, 1, 0);
-        assert(heap.get_meta_block_used_space(0) == sizeof(heap_object_t) + sizeof(heap_write_t) +
+        assert(heap.get_meta_block_used_space(0) == sizeof(heap_object_t) + sizeof(heap_big_write_t) +
             2*dsk.clean_entry_bitmap_size + (dsk.csum_block_size ? dsk.data_block_size/dsk.csum_block_size*4 : 0));
         assert(check_used_space(heap, dsk, 0));
         assert(heap.get_meta_used_space() == heap.get_meta_block_used_space(0));
@@ -188,11 +186,9 @@ void test_mvcc(bool csum)
         assert(count_writes(obj) == 1);
         heap_write_t *wr = obj->get_writes();
         assert(wr->lsn == 1);
-        assert(wr->version == 1);
-        assert(wr->offset == 0);
-        assert(wr->len == dsk.data_block_size);
-        assert(wr->location == 0);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->version == 1);
+        assert(wr->big().location == 0);
         uint64_t old_size = obj->size + wr->size;
 
         assert(heap.read_locked_entry(oid, copy_id) == obj);
@@ -293,11 +289,11 @@ void test_compact_block()
     blockstore_heap_t heap(&dsk, buffer_area.data());
     heap.finish_load();
 
-    uint32_t big_write_size = (sizeof(heap_object_t) + sizeof(heap_write_t) + 2*dsk.clean_entry_bitmap_size + dsk.data_block_size/dsk.csum_block_size*4);
-    uint32_t small_write_size = (sizeof(heap_write_t) + dsk.clean_entry_bitmap_size + 4);
-    assert(big_write_size == 198);
+    uint32_t big_write_size = (sizeof(heap_object_t) + sizeof(heap_big_write_t) + 2*dsk.clean_entry_bitmap_size + dsk.data_block_size/dsk.csum_block_size*4);
+    uint32_t small_write_size = (sizeof(heap_small_write_t) + dsk.clean_entry_bitmap_size + 4);
+    assert(big_write_size == 190);
     assert(small_write_size == 45);
-    uint32_t nwr = dsk.meta_block_size/(big_write_size+small_write_size);
+    uint32_t nwr = (dsk.meta_block_size-heap.get_max_write_entry_size())/(big_write_size+small_write_size);
 
     {
         for (uint32_t i = 0; i < nwr*2; i++)
@@ -319,8 +315,7 @@ void test_compact_block()
         _test_big_write(heap, dsk, 1, nwr*2*0x20000, 1, nwr*2*0x20000);
         _test_big_write(heap, dsk, 1, (nwr*2+1)*0x20000, 1, (nwr*2+1)*0x20000);
         _test_big_write(heap, dsk, 1, (nwr*2+2)*0x20000, 1, (nwr*2+2)*0x20000);
-        assert(count_free_fragments(heap, dsk, 0) == nwr+1);
-        assert(count_free_fragments(heap, dsk, 1) == 1);
+        assert(count_free_fragments(heap, dsk, 0) == 1);
     }
 
     printf("OK test_compact_block\n");
@@ -562,11 +557,9 @@ void test_recheck(bool async, bool csum, bool intent)
         assert(count_writes(obj) == 1);
         heap_write_t *wr = obj->get_writes();
         assert(wr->lsn == 1);
-        assert(wr->version == 1);
-        assert(wr->offset == 0);
-        assert(wr->len == dsk.data_block_size);
-        assert(wr->location == 0x20000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->version == 1);
+        assert(wr->big().location == 0x20000);
 
         // read object 2 - both writes should be present
         oid = { .inode = INODE_WITH_POOL(1, 2), .stripe = 0 };
@@ -575,11 +568,11 @@ void test_recheck(bool async, bool csum, bool intent)
         assert(count_writes(obj) == 2);
         wr = obj->get_writes();
         assert(wr->lsn == 4);
-        assert(wr->version == 2);
-        assert(wr->offset == 8192);
-        assert(wr->len == 12*1024);
-        assert(wr->location == 24*1024);
         assert(wr->entry_type == BS_HEAP_SMALL_WRITE|BS_HEAP_STABLE);
+        assert(wr->version == 2);
+        assert(wr->small().offset == 8192);
+        assert(wr->small().len == 12*1024);
+        assert(wr->small().location == 24*1024);
     }
 
     printf("OK test_recheck %s %s %s\n", async ? "async" : "sync", csum ? "csum" : "no_csum", intent ? "intent" : "buffered");
@@ -616,9 +609,6 @@ void test_corruption()
         uint8_t wr_buf[heap.get_max_write_entry_size()];
         heap_write_t *wr = (heap_write_t*)wr_buf;
         wr->version = 2;
-        wr->offset = 0;
-        wr->len = 0;
-        wr->location = 0;
         wr->entry_type = BS_HEAP_TOMBSTONE|BS_HEAP_STABLE;
         assert(!wr->get_checksums(&heap));
         res = heap.post_write(oid, wr, NULL, NULL);
@@ -657,8 +647,8 @@ void test_corruption()
         assert(obj);
         assert(count_writes(obj) == 1);
         heap_write_t *wr = obj->get_writes();
-        assert(wr->location == 0x40000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->big().location == 0x40000);
 
         // object 3 should be present
         oid = { .inode = INODE_WITH_POOL(1, 1), .stripe = 0x40000 };
@@ -666,8 +656,8 @@ void test_corruption()
         assert(obj);
         assert(count_writes(obj) == 1);
         wr = obj->get_writes();
-        assert(wr->location == 0x60000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->big().location == 0x60000);
 
         // object 4 should be a tombstone
         oid = { .inode = INODE_WITH_POOL(1, 1), .stripe = 0x60000 };
@@ -742,12 +732,12 @@ void test_full_overwrite(bool stable)
         assert(count_writes(obj) == 2);
         heap_write_t *wr = obj->get_writes();
         assert(wr->version == 4);
-        assert(wr->location == 20480);
         assert(wr->entry_type == BS_HEAP_SMALL_WRITE|BS_HEAP_STABLE);
+        assert(wr->small().location == 20480);
         wr = wr->next();
         assert(wr->version == 3);
-        assert(wr->location == 0x40000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->big().location == 0x40000);
 
         // check that the data block 0x20000 is freed and 0x40000 is used
         assert(!heap.is_data_used(0x20000));
@@ -852,7 +842,7 @@ void _test_invalid_data_setup(blockstore_disk_t & dsk, std::vector<uint8_t> & bu
     wr->lsn = 1;
     wr->version = 1;
     wr->entry_type = BS_HEAP_TOMBSTONE;
-    wr->size = sizeof(heap_write_t);
+    wr->size = sizeof(heap_tombstone_t);
     obj->crc32c = obj->calc_crc32c();
 
     obj = (heap_object_t*)((uint8_t*)wr + wr->size);
@@ -865,7 +855,7 @@ void _test_invalid_data_setup(blockstore_disk_t & dsk, std::vector<uint8_t> & bu
     wr->lsn = 1;
     wr->version = 1;
     wr->entry_type = BS_HEAP_TOMBSTONE;
-    wr->size = sizeof(heap_write_t);
+    wr->size = sizeof(heap_tombstone_t);
     obj->crc32c = obj->calc_crc32c();
 
     obj = (heap_object_t*)(tmp.data() + dsk.meta_block_size);
@@ -877,7 +867,7 @@ void _test_invalid_data_setup(blockstore_disk_t & dsk, std::vector<uint8_t> & bu
     wr->lsn = 2;
     wr->version = 1;
     wr->entry_type = BS_HEAP_TOMBSTONE;
-    wr->size = sizeof(heap_write_t);
+    wr->size = sizeof(heap_tombstone_t);
     obj->crc32c = obj->calc_crc32c();
 }
 
@@ -889,6 +879,7 @@ void test_invalid_data()
     std::vector<uint8_t> tmp;
 
     // Too small object
+    printf("too small:\n");
     {
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         heap_object_t *obj = (heap_object_t*)tmp.data();
@@ -907,6 +898,7 @@ void test_invalid_data()
     }
 
     // Too large object
+    printf("too large:\n");
     {
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         heap_object_t *obj = (heap_object_t*)tmp.data();
@@ -925,6 +917,7 @@ void test_invalid_data()
     }
 
     // No writes
+    printf("no writes:\n");
     {
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         heap_object_t *obj = (heap_object_t*)tmp.data();
@@ -946,6 +939,7 @@ void test_invalid_data()
     }
 
     // Bad crc32c
+    printf("bad crc:\n");
     {
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         heap_object_t *obj = (heap_object_t*)tmp.data();
@@ -967,6 +961,7 @@ void test_invalid_data()
     }
 
     // Bad write size
+    printf("bad write size:\n");
     {
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         heap_object_t *obj = (heap_object_t*)tmp.data();
@@ -991,15 +986,16 @@ void test_invalid_data()
     // 4) intersects with object beginning
     for (int i = 0; i < 4; i++)
     {
+        printf("bad write positions - %d:\n", i);
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         tmp.resize(dsk.meta_block_size*3);
         memmove(tmp.data()+dsk.meta_block_size, tmp.data(), 2*dsk.meta_block_size);
         memset(tmp.data(), 0, dsk.meta_block_size);
-        heap_object_t *obj = (heap_object_t*)(tmp.data() + dsk.meta_block_size + sizeof(heap_object_t) + sizeof(heap_write_t));
+        heap_object_t *obj = (heap_object_t*)(tmp.data() + dsk.meta_block_size + sizeof(heap_object_t) + sizeof(heap_tombstone_t));
         if (i == 0)
-            obj->write_pos = -(int16_t)(sizeof(heap_object_t)+sizeof(heap_write_t)+1);
+            obj->write_pos = -(int16_t)(sizeof(heap_object_t)+sizeof(heap_tombstone_t)+1);
         else if (i == 1)
-            obj->write_pos = dsk.meta_block_size-sizeof(heap_object_t)-2*sizeof(heap_write_t)+1;
+            obj->write_pos = dsk.meta_block_size-sizeof(heap_object_t)-2*sizeof(heap_tombstone_t)+1;
         else if (i == 2)
             obj->write_pos = -1;
         else if (i == 3)
@@ -1022,16 +1018,17 @@ void test_invalid_data()
 
     // Object write intersects with other writes
     {
+        printf("write intersections:\n");
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         // Object2 Object1 BadLength Write2
         uint8_t *nb = tmp.data() + dsk.meta_block_size;
-        memcpy(nb, tmp.data() + sizeof(heap_object_t) + sizeof(heap_write_t), sizeof(heap_object_t));
+        memcpy(nb, tmp.data() + sizeof(heap_object_t) + sizeof(heap_tombstone_t), sizeof(heap_object_t));
         nb += sizeof(heap_object_t);
         memcpy(nb, tmp.data(), sizeof(heap_object_t));
         nb += sizeof(heap_object_t);
-        *((uint16_t*)nb) = sizeof(heap_write_t) + 4;
+        *((uint16_t*)nb) = sizeof(heap_tombstone_t) + 4;
         nb += 2;
-        memcpy(nb, tmp.data() + 2*sizeof(heap_object_t) + sizeof(heap_write_t), sizeof(heap_write_t));
+        memcpy(nb, tmp.data() + 2*sizeof(heap_object_t) + sizeof(heap_tombstone_t), sizeof(heap_write_t));
 
         heap_object_t *obj = (heap_object_t*)(tmp.data() + dsk.meta_block_size);
         obj->write_pos = 2*sizeof(heap_object_t) + 2;
@@ -1057,12 +1054,13 @@ void test_invalid_data()
     // Write list entry exceeds block boundaries
     for (int i = 0; i < 2; i++)
     {
+        printf("write exceeds boundary - %d:\n", i);
         _test_invalid_data_setup(dsk, buffer_area, tmp);
         tmp.resize(dsk.meta_block_size*3);
         memmove(tmp.data()+dsk.meta_block_size, tmp.data(), 2*dsk.meta_block_size);
         memset(tmp.data(), 0, dsk.meta_block_size);
         heap_object_t *obj = (heap_object_t*)(tmp.data() + dsk.meta_block_size);
-        obj->get_writes()->next_pos = (i == 0 ? -sizeof(heap_object_t)-1 : dsk.meta_block_size - sizeof(heap_object_t) - sizeof(heap_write_t) + 1);
+        obj->get_writes()->next_pos = (i == 0 ? -sizeof(heap_object_t)-1 : dsk.meta_block_size - sizeof(heap_object_t) - sizeof(heap_tombstone_t) + 1);
         obj->crc32c = obj->calc_crc32c();
 
         blockstore_heap_t heap(&dsk, buffer_area.data());
@@ -1182,13 +1180,13 @@ void test_rollback()
         assert(count_writes(obj) == 2);
         heap_write_t *wr = obj->get_writes();
         assert(wr->version == 2);
-        assert(wr->location == 16384);
-        assert(wr->len == 4096);
         assert(wr->entry_type == BS_HEAP_SMALL_WRITE|BS_HEAP_STABLE);
+        assert(wr->small().location == 16384);
+        assert(wr->small().len == 4096);
         wr = wr->next();
         assert(wr->version == 1);
-        assert(wr->location == 0x20000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->big().location == 0x20000);
 
         assert(heap.is_data_used(0x20000));
         assert(!heap.is_data_used(0x40000));
@@ -1298,12 +1296,14 @@ void test_full_alloc()
     heap.finish_load();
     assert(heap.get_meta_total_space() == 4*4096);
 
-    uint32_t big_write_size = (sizeof(heap_object_t) + sizeof(heap_write_t) + 2*dsk.clean_entry_bitmap_size + dsk.data_block_size/dsk.csum_block_size*4);
-    uint32_t small_write_size = (sizeof(heap_write_t) + dsk.clean_entry_bitmap_size + 4);
-    assert(big_write_size == 198);
+    uint32_t big_write_size = (sizeof(heap_object_t) + sizeof(heap_big_write_t) + 2*dsk.clean_entry_bitmap_size + dsk.data_block_size/dsk.csum_block_size*4);
+    uint32_t small_write_size = (sizeof(heap_small_write_t) + dsk.clean_entry_bitmap_size + 4);
+    assert(big_write_size == 190);
     assert(small_write_size == 45);
-    uint32_t b_4s = (big_write_size + 4*small_write_size); // 377
-    uint32_t epb = (4096-800+b_4s-1)/b_4s; // entries per block
+    uint32_t b_4s = (big_write_size + 4*small_write_size);
+    assert(b_4s == 370);
+    const uint32_t min_alloc = (sizeof(heap_object_t) + sizeof(heap_tombstone_t));
+    uint32_t epb = (4096 - 800 + 800 % min_alloc + b_4s-1) / b_4s;
     for (int j = 0; j < 4; j++)
     {
         assert(heap.get_meta_nearfull_blocks() == j);
@@ -1322,27 +1322,29 @@ void test_full_alloc()
     }
 
     // After filling all blocks to (4096-800), most free blocks should start to be allocated first
-    for (int i = 0; i < 8; i++)
+    const int nwr2 = 12;
+    for (int i = 0; i < nwr2; i++)
     {
         assert(heap.get_meta_nearfull_blocks() == 4);
-        _test_big_write(heap, dsk, 1, (40+i)*0x20000, 1, (40+i)*0x20000);
+        _test_big_write(heap, dsk, 1, (epb*4+i)*0x20000, 1, (epb*4+i)*0x20000);
     }
     for (int i = 0; i < 4; i++)
     {
-        assert(heap.get_meta_block_used_space(i) == (epb*b_4s + big_write_size*2));
+        assert(heap.get_meta_block_used_space(i) == (epb*b_4s + big_write_size*3));
     }
 
     // New writes are prevented if it may lead to inability to overwrite any object
     // - i.e. if the block doesn't have at least <max_overwrite_size> free space as the result
-    assert(_test_do_big_write(heap, dsk, 1, 48*0x20000, 1, 48*0x20000) == ENOSPC);
+    assert(_test_do_big_write(heap, dsk, 1, (epb*4+nwr2)*0x20000, 1, (epb*4+nwr2)*0x20000) == ENOSPC);
 
     // Overwrites are, however, allowed until the block is almost empty
-    for (int i = 0; i < 6; i++)
+    const int nwr3 = 4;
+    for (int i = 0; i < nwr3; i++)
     {
         assert(_test_do_small_write(heap, dsk, 1, 0, 6+i, 0, 4096, epb*4*16384+i*4096) == 0);
     }
     assert(dsk.meta_block_size-heap.get_meta_block_used_space(0) < big_write_size);
-    assert(_test_do_small_write(heap, dsk, 1, 0, 12, 0, 4096, 48*16384+8*4096) == EAGAIN);
+    assert(_test_do_small_write(heap, dsk, 1, 0, 6+nwr3, 0, 4096, 48*16384+8*4096) == EAGAIN);
 
     // Check that used_alloc_queue doesn't return used blocks
     {
@@ -1407,8 +1409,8 @@ void test_duplicate()
         assert(count_writes(obj) == 1);
         heap_write_t *wr = obj->get_writes();
         assert(wr->version == 2);
-        assert(wr->location == 0x40000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->big().location == 0x40000);
 
         assert(heap.get_meta_block_used_space(0) == 0);
         assert(heap.get_meta_block_used_space(1) == obj->size+wr->size);
@@ -1431,8 +1433,8 @@ void test_duplicate()
         assert(count_writes(obj) == 1);
         heap_write_t *wr = obj->get_writes();
         assert(wr->version == 2);
-        assert(wr->location == 0x40000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->big().location == 0x40000);
 
         assert(heap.get_meta_block_used_space(0) == 0);
         assert(heap.get_meta_block_used_space(1) == obj->size+wr->size);
@@ -1500,25 +1502,23 @@ void test_autocompact(bool csum)
         assert(count_writes(obj) == 3);
         heap_write_t *wr = obj->get_writes();
         assert(wr->lsn == 5);
-        assert(wr->version == 5);
-        assert(wr->offset == 7*4096);
-        assert(wr->len == 4096);
-        assert(wr->location == 7*4096);
         assert(wr->entry_type == BS_HEAP_SMALL_WRITE|BS_HEAP_STABLE);
+        assert(wr->version == 5);
+        assert(wr->small().offset == 7*4096);
+        assert(wr->small().len == 4096);
+        assert(wr->small().location == 7*4096);
         wr = wr->next();
         assert(wr->lsn == 4);
-        assert(wr->version == 4);
-        assert(wr->offset == 5*4096);
-        assert(wr->len == 4096);
-        assert(wr->location == 6*4096);
         assert(wr->entry_type == BS_HEAP_SMALL_WRITE|BS_HEAP_STABLE);
+        assert(wr->version == 4);
+        assert(wr->small().offset == 5*4096);
+        assert(wr->small().len == 4096);
+        assert(wr->small().location == 6*4096);
         wr = wr->next();
         assert(wr->lsn == 3);
-        assert(wr->version == 3);
-        assert(wr->offset == 0);
-        assert(wr->len == dsk.data_block_size);
-        assert(wr->location == 0x20000);
         assert(wr->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
+        assert(wr->version == 3);
+        assert(wr->big().location == 0x20000);
 
         // check that blocks are auto-freed
         assert(heap.is_data_used(0x20000));
@@ -1558,8 +1558,7 @@ void test_intent_write(bool csum)
         assert(obj);
         assert(count_writes(obj) == 2); // intent overwrites previous intent
         assert(obj->get_writes()->lsn == 3);
-        assert(obj->get_writes()->next()->offset == 0);
-        assert(obj->get_writes()->next()->len == 12288);
+        assert(obj->get_writes()->next()->entry_type == BS_HEAP_BIG_WRITE|BS_HEAP_STABLE);
 
         uint8_t ref_int_bitmap[dsk.clean_entry_bitmap_size];
         memset(ref_int_bitmap, 0, dsk.clean_entry_bitmap_size);
@@ -1599,9 +1598,9 @@ void test_move()
     heap.finish_load();
     assert(heap.get_meta_total_space() == 4*4096);
 
-    uint32_t big_write_size = (sizeof(heap_object_t) + sizeof(heap_write_t) + 2*dsk.clean_entry_bitmap_size + dsk.data_block_size/dsk.csum_block_size*4);
-    uint32_t small_write_size = (sizeof(heap_write_t) + dsk.clean_entry_bitmap_size + 4);
-    assert(big_write_size == 198);
+    uint32_t big_write_size = (sizeof(heap_object_t) + sizeof(heap_big_write_t) + 2*dsk.clean_entry_bitmap_size + dsk.data_block_size/dsk.csum_block_size*4);
+    uint32_t small_write_size = (sizeof(heap_small_write_t) + dsk.clean_entry_bitmap_size + 4);
+    assert(big_write_size == 190);
     assert(small_write_size == 45);
 
     // Fill block 1 almost completely with unstable small writes