diff --git a/src/blockstore/blockstore_flush.cpp b/src/blockstore/blockstore_flush.cpp
index ff347e97..29c7411c 100644
--- a/src/blockstore/blockstore_flush.cpp
+++ b/src/blockstore/blockstore_flush.cpp
@@ -476,7 +476,8 @@ 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->small().offset/bs->dsk.csum_block_size)*(bs->dsk.data_csum_type & 0xFF)));
+                - ((wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_BIG_INTENT)
+                    ? 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)
diff --git a/src/blockstore/blockstore_heap.cpp b/src/blockstore/blockstore_heap.cpp
index 6c510711..f2e934be 100644
--- a/src/blockstore/blockstore_heap.cpp
+++ b/src/blockstore/blockstore_heap.cpp
@@ -42,13 +42,16 @@ uint32_t blockstore_heap_t::get_simple_entry_size()
 
 uint32_t blockstore_heap_t::get_big_entry_size()
 {
-    // We always store full checksums for "big" entries to prevent ENOSPC on compaction
-    // when (big_write+small_write) are smaller than (compacted big_write)
-    // However, we only use part of it related to offset..offset+len
     return sizeof(heap_big_write_t) + dsk->clean_entry_bitmap_size*2 +
         (!dsk->data_csum_type ? 0 : dsk->data_block_size/dsk->csum_block_size * (dsk->data_csum_type & 0xFF));
 }
 
+uint32_t blockstore_heap_t::get_big_intent_entry_size()
+{
+    return sizeof(heap_big_intent_t) + dsk->clean_entry_bitmap_size*2 +
+        (!dsk->data_csum_type ? 4 : dsk->data_block_size/dsk->csum_block_size * (dsk->data_csum_type & 0xFF));
+}
+
 uint32_t blockstore_heap_t::get_small_entry_size(uint32_t offset, uint32_t len)
 {
     return sizeof(heap_small_write_t) + dsk->clean_entry_bitmap_size +
@@ -77,7 +80,8 @@ uint32_t blockstore_heap_t::get_csum_size(uint32_t entry_type, uint32_t offset,
         return ((dsk->data_csum_type & 0xFF) *
             ((offset+len+dsk->csum_block_size-1)/dsk->csum_block_size - offset/dsk->csum_block_size));
     }
-    else if ((entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE)
+    else if ((entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_WRITE ||
+        (entry_type & BS_HEAP_TYPE) == BS_HEAP_BIG_INTENT)
     {
         return (dsk->data_block_size/dsk->csum_block_size * (dsk->data_csum_type & 0xFF));
     }
@@ -90,6 +94,10 @@ uint32_t heap_entry_t::get_size(blockstore_heap_t *heap)
     {
         return heap->get_big_entry_size();
     }
+    if (type() == BS_HEAP_BIG_INTENT)
+    {
+        return heap->get_big_intent_entry_size();
+    }
     if (type() == BS_HEAP_SMALL_WRITE || type() == BS_HEAP_INTENT_WRITE)
     {
         return heap->get_small_entry_size(small().offset, small().len);
@@ -100,6 +108,7 @@ uint32_t heap_entry_t::get_size(blockstore_heap_t *heap)
 bool heap_entry_t::is_overwrite()
 {
     return ((entry_type & ~BS_HEAP_GARBAGE) == (BS_HEAP_BIG_WRITE|BS_HEAP_STABLE) ||
+        (entry_type & ~BS_HEAP_GARBAGE) == (BS_HEAP_BIG_INTENT|BS_HEAP_STABLE) ||
         (entry_type & ~BS_HEAP_GARBAGE) == (BS_HEAP_DELETE|BS_HEAP_STABLE));
 }
 
@@ -127,16 +136,22 @@ void heap_entry_t::set_garbage()
 
 uint8_t *heap_entry_t::get_ext_bitmap(blockstore_heap_t *heap)
 {
-    if (type() == BS_HEAP_DELETE)
-        return NULL;
-    return ((uint8_t*)this + (type() == BS_HEAP_BIG_WRITE ? sizeof(heap_big_write_t) : sizeof(heap_small_write_t)));
+    if (type() == BS_HEAP_SMALL_WRITE || type() == BS_HEAP_INTENT_WRITE)
+        return ((uint8_t*)this + sizeof(heap_small_write_t));
+    else if (type() == BS_HEAP_BIG_WRITE)
+        return ((uint8_t*)this + sizeof(heap_big_write_t));
+    else if (type() == BS_HEAP_BIG_INTENT)
+        return ((uint8_t*)this + sizeof(heap_big_intent_t));
+    return NULL;
 }
 
 uint8_t *heap_entry_t::get_int_bitmap(blockstore_heap_t *heap)
 {
-    if (type() != BS_HEAP_BIG_WRITE)
-        return NULL;
-    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);
+    if (type() == BS_HEAP_BIG_WRITE)
+        return ((uint8_t*)this + sizeof(heap_big_write_t) + heap->dsk->clean_entry_bitmap_size);
+    else if (type() == BS_HEAP_BIG_INTENT)
+        return ((uint8_t*)this + sizeof(heap_big_intent_t) + heap->dsk->clean_entry_bitmap_size);
+    return NULL;
 }
 
 uint8_t *heap_entry_t::get_checksums(blockstore_heap_t *heap)
@@ -145,20 +160,26 @@ uint8_t *heap_entry_t::get_checksums(blockstore_heap_t *heap)
         return NULL;
     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_big_write_t) + 2*heap->dsk->clean_entry_bitmap_size);
+    if (type() == BS_HEAP_BIG_WRITE)
+        return ((uint8_t*)this + sizeof(heap_big_write_t) + 2*heap->dsk->clean_entry_bitmap_size);
+    if (type() == BS_HEAP_BIG_INTENT)
+        return ((uint8_t*)this + sizeof(heap_big_intent_t) + 2*heap->dsk->clean_entry_bitmap_size);
+    return NULL;
 }
 
 uint32_t *heap_entry_t::get_checksum(blockstore_heap_t *heap)
 {
-    if (heap->dsk->csum_block_size ||
-        type() != BS_HEAP_SMALL_WRITE && type() != BS_HEAP_INTENT_WRITE ||
-        small().len == 0)
+    if (type() == BS_HEAP_SMALL_WRITE || type() == BS_HEAP_INTENT_WRITE)
     {
-        return NULL;
+        if (heap->dsk->csum_block_size || small().len == 0)
+            return NULL;
+        return (uint32_t*)((uint8_t*)this + sizeof(heap_small_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);
+    if (type() == BS_HEAP_BIG_INTENT)
+    {
+        return (uint32_t*)((uint8_t*)this + sizeof(heap_big_intent_t) + 2*heap->dsk->clean_entry_bitmap_size);
+    }
+    return NULL;
 }
 
 uint64_t heap_entry_t::big_location(blockstore_heap_t *heap)
@@ -199,7 +220,7 @@ blockstore_heap_t::blockstore_heap_t(blockstore_disk_t *dsk, uint8_t *buffer_are
     buffer_area(buffer_area),
     log_level(log_level),
     meta_block_count(dsk->meta_area_size/dsk->meta_block_size-1), // first block is the superblock
-    big_entry_size(get_big_entry_size())
+    max_entry_size(get_big_intent_entry_size())
 {
     assert(dsk->meta_block_size < 32768);
     assert(dsk->meta_area_size > 0);
@@ -268,6 +289,7 @@ int blockstore_heap_t::read_blocks(uint64_t disk_offset, uint64_t disk_size, uin
                 block_offset += (wr->size & ~FREE_SPACE_BIT);
                 continue;
             }
+            wr->entry_type &= ~BS_HEAP_GARBAGE;
             if ((wr->entry_type & BS_HEAP_TYPE) < BS_HEAP_BIG_WRITE ||
                 (wr->entry_type & BS_HEAP_TYPE) > BS_HEAP_ROLLBACK ||
                 (wr->entry_type & ~(BS_HEAP_TYPE|BS_HEAP_STABLE)))
@@ -338,7 +360,7 @@ int blockstore_heap_t::load_blocks(uint64_t disk_offset, uint64_t size, uint8_t
         modify_alloc(block_num, [&](heap_block_info_t & inf)
         {
             if (!inf.entries.size())
-                inf.entries.reserve(dsk->meta_block_size / sizeof(heap_entry_t));
+                inf.entries.reserve(dsk->meta_block_size / sizeof(heap_entry_t)); // FIXME maybe less
             inf.entries.push_back(li);
             if (!wr->is_garbage())
                 inf.used_space += wr->size;
@@ -352,6 +374,7 @@ int blockstore_heap_t::load_blocks(uint64_t disk_offset, uint64_t size, uint8_t
 
 void blockstore_heap_t::fill_recheck_queue()
 {
+    // FIXME: Validate objects
     for (auto & pgp: block_index)
     {
         for (auto & ip: pgp.second)
@@ -359,9 +382,10 @@ void blockstore_heap_t::fill_recheck_queue()
             for (auto & op: ip.second)
             {
                 auto obj = &op.second.ptr->entry;
-                if (obj->type() == BS_HEAP_INTENT_WRITE)
+                if (obj->type() == BS_HEAP_INTENT_WRITE || obj->type() == BS_HEAP_BIG_INTENT)
                 {
                     // Recheck only the latest intent_write
+                    // FIXME Save checked_lsn in the superblock
                     recheck_queue.push_back(obj);
                 }
                 else
@@ -410,6 +434,10 @@ void blockstore_heap_t::mark_used_blocks()
                     {
                         use_data(wr->inode, wr->big_location(this));
                     }
+                    else if (wr->type() == BS_HEAP_BIG_INTENT)
+                    {
+                        use_data(wr->inode, wr->big_intent().block_num * dsk->data_block_size);
+                    }
                     if (wr->is_compactable() && !added)
                     {
                         compact_queue.push_back((object_id){ .inode = wr->inode, .stripe = wr->stripe });
@@ -441,6 +469,7 @@ void blockstore_heap_t::recheck_buffer(heap_entry_t *cwr, uint8_t *buf)
                 }
             }
         });
+        // FIXME: Write recheck_modified_blocks to disk
         recheck_modified_blocks.insert(block_num);
     };
     if (cwr->is_garbage())
@@ -503,33 +532,55 @@ bool blockstore_heap_t::recheck_small_writes(std::function<void(bool is_data, ui
     {
         heap_entry_t *wr = recheck_queue.front();
         recheck_queue.pop_front();
-        bool is_intent = wr->type() == BS_HEAP_INTENT_WRITE;
-        uint64_t loc = wr->small().location;
-        if (is_intent)
+        bool from_data = false;
+        uint64_t loc = 0;
+        uint32_t len = 0;
+        if (wr->type() == BS_HEAP_INTENT_WRITE)
         {
             auto prev_wr = prev(wr);
-            if (!prev_wr || prev_wr->entry_type != (BS_HEAP_BIG_WRITE | (wr->entry_type & BS_HEAP_STABLE)) && prev_wr->entry_type != wr->entry_type)
+            while (prev_wr && prev_wr->entry_type == wr->entry_type)
+            {
+                // Skip other intent_writes
+                prev_wr = prev(prev_wr);
+            }
+            if (!prev_wr || prev_wr->entry_type != (BS_HEAP_BIG_WRITE | (wr->entry_type & BS_HEAP_STABLE)) &&
+                prev_wr->entry_type != (BS_HEAP_BIG_INTENT | (wr->entry_type & BS_HEAP_STABLE)))
             {
                 fprintf(stderr, "Error: intent_write entry %jx:%jx v%ju l%ju is not written over a big_write\n",
                     wr->inode, wr->stripe, wr->version, wr->lsn);
                 exit(1);
             }
             loc = wr->small().offset + prev_wr->big_location(this);
+            len = wr->small().len;
+            from_data = true;
+        }
+        else if (wr->type() == BS_HEAP_BIG_INTENT)
+        {
+            auto & bi = wr->big_intent();
+            loc = bi.block_num * dsk->data_block_size + bi.offset;
+            len = bi.len;
+            from_data = true;
+        }
+        else
+        {
+            assert(wr->type() == BS_HEAP_SMALL_WRITE);
+            loc = wr->small().location;
+            len = wr->small().len;
         }
         if (log_level > 5)
         {
             fprintf(stderr, "Notice: rechecking %u bytes at %ju in %s area (lsn %ju)\n",
-                wr->small().len, loc, is_intent ? "data" : "buffer", wr->lsn);
+                len, loc, from_data ? "data" : "buffer", wr->lsn);
         }
-        if (!is_intent && buffer_area)
+        if (!from_data && buffer_area)
         {
             recheck_buffer(wr, buffer_area+loc);
         }
         else
         {
             recheck_in_progress++;
-            uint8_t *buf = (uint8_t*)memalign_or_die(MEM_ALIGNMENT, wr->small().len);
-            recheck_cb(is_intent, loc, wr->small().len, buf, [this, wr, buf]()
+            uint8_t *buf = (uint8_t*)memalign_or_die(MEM_ALIGNMENT, len);
+            recheck_cb(from_data, loc, len, buf, [this, wr, buf]()
             {
                 recheck_buffer(wr, buf);
                 free(buf);
@@ -584,7 +635,14 @@ bool blockstore_heap_t::calc_checksums(heap_entry_t *wr, uint8_t *data, bool set
         {
             return true;
         }
-        uint32_t real_csum = crc32c(0, data, wr->small().len);
+        uint32_t len = 0;
+        if (wr->type() == BS_HEAP_SMALL_WRITE || wr->type() == BS_HEAP_INTENT_WRITE)
+            len = wr->small().len;
+        else if (wr->type() == BS_HEAP_BIG_INTENT)
+            len = wr->big_intent().len;
+        else
+            assert(0);
+        uint32_t real_csum = crc32c(0, data, len);
         if (set)
         {
             *wr_csum = real_csum;
@@ -597,6 +655,13 @@ bool blockstore_heap_t::calc_checksums(heap_entry_t *wr, uint8_t *data, bool set
         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);
     }
+    if (wr->type() == BS_HEAP_BIG_INTENT)
+    {
+        auto & bi = wr->big_intent();
+        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), bi.offset, bi.offset+bi.len, set, NULL);
+    }
+    assert(wr->type() == BS_HEAP_SMALL_WRITE || wr->type() == BS_HEAP_INTENT_WRITE);
     return calc_block_checksums((uint32_t*)wr->get_checksums(this), data, NULL,
         wr->small().offset, wr->small().offset+wr->small().len, set, NULL);
 }
@@ -803,10 +868,10 @@ int blockstore_heap_t::allocate_entry(uint32_t entry_size, uint32_t *block_num,
         // First try to write into the same block as the previous time
         auto & inf = block_info.at(last_allocated_block);
         auto free_space = dsk->meta_block_size - inf.used_space;
-        if (inf.is_writing || free_space < entry_size /* FIXME edge cases with +2? */ ||
+        if (inf.is_writing || free_space < entry_size ||
             // Do not allow to make the last non-nearfull block nearfull
             !allow_last_free && meta_nearfull_blocks >= meta_block_count-1 &&
-            free_space >= big_entry_size && free_space < big_entry_size+entry_size)
+            free_space >= max_entry_size && free_space < max_entry_size+entry_size)
         {
             last_allocated_block = UINT32_MAX;
         }
@@ -824,7 +889,7 @@ int blockstore_heap_t::allocate_entry(uint32_t entry_size, uint32_t *block_num,
             // Do not allow to make the last non-nearfull block nearfull
             auto & inf = block_info.at(last_allocated_block);
             auto free_space = dsk->meta_block_size - inf.used_space;
-            if (free_space >= big_entry_size && free_space < big_entry_size+entry_size)
+            if (free_space >= max_entry_size && free_space < max_entry_size+entry_size)
             {
                 last_allocated_block = UINT32_MAX;
             }
@@ -853,8 +918,8 @@ int blockstore_heap_t::allocate_entry(uint32_t entry_size, uint32_t *block_num,
     {
         // Do not allow to make the last non-nearfull block nearfull
         auto & inf = block_info.at(last_allocated_block);
-        if (dsk->meta_block_size-inf.used_space >= big_entry_size &&
-            dsk->meta_block_size-inf.used_space+entry_size < big_entry_size)
+        if (dsk->meta_block_size-inf.used_space >= max_entry_size &&
+            dsk->meta_block_size-inf.used_space+entry_size < max_entry_size)
         {
             last_allocated_block = UINT32_MAX;
             return ENOSPC;
@@ -944,7 +1009,7 @@ int blockstore_heap_t::add_entry(uint32_t wr_size, uint32_t *modified_block,
     auto new_wr = &li->entry;
     auto & inf = block_info.at(block_num);
     if (!inf.entries.size())
-        inf.entries.reserve(dsk->meta_block_size / sizeof(heap_entry_t));
+        inf.entries.reserve(dsk->meta_block_size / sizeof(heap_entry_t)); // FIXME Maybe less
     inf.entries.push_back(li);
     assert(!inf.mod_lsn_to || inf.mod_lsn_to == next_lsn);
     new_wr->lsn = ++next_lsn;
@@ -1027,6 +1092,50 @@ int blockstore_heap_t::add_big_write(object_id oid, heap_entry_t *old_head, bool
     });
 }
 
+int blockstore_heap_t::add_big_intent(object_id oid, heap_entry_t *old_head, uint64_t version,
+    uint32_t offset, uint32_t len, uint8_t *bitmap, uint8_t *data, uint8_t *checksums, uint32_t *modified_block)
+{
+    if (!old_head ||
+        old_head->entry_type != (BS_HEAP_BIG_INTENT|BS_HEAP_STABLE) &&
+        old_head->entry_type != (BS_HEAP_BIG_WRITE|BS_HEAP_STABLE) ||
+        dsk->csum_block_size > dsk->bitmap_granularity && !checksums)
+    {
+        return EINVAL;
+    }
+    uint32_t wr_size = get_big_intent_entry_size();
+    return add_entry(wr_size, modified_block, false, [&](heap_entry_t *wr)
+    {
+        wr->entry_type = BS_HEAP_BIG_INTENT | BS_HEAP_STABLE;
+        wr->inode = oid.inode;
+        wr->stripe = oid.stripe;
+        wr->version = version;
+        auto & bi = wr->big_intent();
+        bi.offset = offset;
+        bi.len = len;
+        bi.block_num = (old_head->type() == BS_HEAP_BIG_INTENT
+            ? old_head->big_intent().block_num
+            : old_head->big().block_num);
+        if (bitmap)
+            memcpy(wr->get_ext_bitmap(this), bitmap, dsk->clean_entry_bitmap_size);
+        else
+            memcpy(wr->get_ext_bitmap(this), old_head->get_ext_bitmap(this), dsk->clean_entry_bitmap_size);
+        memcpy(wr->get_int_bitmap(this), old_head->get_int_bitmap(this), dsk->clean_entry_bitmap_size);
+        bitmap_set(wr->get_int_bitmap(this), offset, len, dsk->bitmap_granularity);
+        if (dsk->data_csum_type)
+        {
+            if (checksums)
+                memcpy(wr->get_checksums(this), checksums, dsk->clean_entry_bitmap_size);
+            else
+            {
+                memcpy(wr->get_checksums(this), old_head->get_checksums(this), dsk->clean_entry_bitmap_size);
+                calc_checksums(wr, (uint8_t*)data, true, offset, len);
+            }
+        }
+        else
+            calc_checksums(wr, (uint8_t*)data, true);
+    });
+}
+
 int blockstore_heap_t::add_compact(heap_entry_t *obj, uint64_t to_lsn, uint32_t *modified_block, uint8_t *new_csums)
 {
     // Slightly tricky - we don't want to compact an object if it's overwritten or deleted during compaction
@@ -1302,13 +1411,13 @@ uint32_t blockstore_heap_t::meta_alloc_pos(const heap_block_info_t & inf)
         // 100% full - no entry can be written into this block at all
         return META_ALLOC_LEVELS;
     }
-    if (inf.used_space > dsk->meta_block_size-big_entry_size)
+    if (inf.used_space > dsk->meta_block_size-max_entry_size)
     {
         // nearfull - big_entries won't fit into this block so it can't be used for compaction
         return META_ALLOC_LEVELS-1;
     }
     // normal block
-    return inf.used_space / ((dsk->meta_block_size-big_entry_size) / (META_ALLOC_LEVELS-1));
+    return inf.used_space / ((dsk->meta_block_size-max_entry_size+META_ALLOC_LEVELS-2) / (META_ALLOC_LEVELS-1));
 }
 
 void blockstore_heap_t::modify_alloc(uint32_t block_num, std::function<void(heap_block_info_t &)> change_cb)
@@ -1373,7 +1482,7 @@ void blockstore_heap_t::mark_garbage_up_to(heap_entry_t *wr)
         return;
     }
     assert(wr->is_overwrite());
-    uint32_t used_big = (wr->type() == BS_HEAP_BIG_WRITE ? wr->big().block_num : UINT32_MAX);
+    uint32_t used_big = (wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_BIG_INTENT ? wr->big().block_num : UINT32_MAX);
     wr = prev(wr);
     while (wr && !wr->is_garbage())
     {
@@ -1391,7 +1500,7 @@ void blockstore_heap_t::mark_garbage(uint32_t block_num, heap_entry_t *prev_wr,
     {
         free_buffer_area(prev_wr->inode, prev_wr->small().location, prev_wr->small().len);
     }
-    else if (prev_wr->type() == BS_HEAP_BIG_WRITE && prev_wr->big().block_num != used_big)
+    else if ((prev_wr->type() == BS_HEAP_BIG_WRITE || prev_wr->type() == BS_HEAP_BIG_INTENT) && prev_wr->big().block_num != used_big)
     {
         free_data(prev_wr->inode, prev_wr->big_location(this));
     }
diff --git a/src/blockstore/blockstore_heap.h b/src/blockstore/blockstore_heap.h
index 2680cbe4..729ef7f7 100644
--- a/src/blockstore/blockstore_heap.h
+++ b/src/blockstore/blockstore_heap.h
@@ -21,20 +21,22 @@ struct pool_shard_settings_t
     uint32_t pg_stripe_size;
 };
 
-#define BS_HEAP_TYPE 7
+#define BS_HEAP_TYPE 0x07
 #define BS_HEAP_BIG_WRITE 1
 #define BS_HEAP_SMALL_WRITE 2
 #define BS_HEAP_INTENT_WRITE 3
-#define BS_HEAP_DELETE 4
-#define BS_HEAP_COMMIT 5
-#define BS_HEAP_ROLLBACK 6
-#define BS_HEAP_STABLE 8
-#define BS_HEAP_GARBAGE 16
+#define BS_HEAP_BIG_INTENT 4
+#define BS_HEAP_DELETE 5
+#define BS_HEAP_COMMIT 6
+#define BS_HEAP_ROLLBACK 7
+#define BS_HEAP_STABLE 0x40
+#define BS_HEAP_GARBAGE 0x80
 
 class blockstore_heap_t;
 
 struct heap_small_write_t;
 struct heap_big_write_t;
+struct heap_big_intent_t;
 
 struct __attribute__((__packed__)) heap_entry_t
 {
@@ -53,6 +55,7 @@ struct __attribute__((__packed__)) heap_entry_t
     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; }
+    inline heap_big_intent_t& big_intent() { return *(heap_big_intent_t*)this; }
     bool is_garbage();
     void set_garbage();
     bool is_overwrite();
@@ -75,6 +78,8 @@ struct __attribute__((__packed__)) heap_small_write_t
     uint64_t location; // FIXME: change to uint32_t and shift by block size
     uint32_t offset;
     uint32_t len;
+
+    // Also includes 1 bitmap and 1 crc32c after the bitmap if checksums are disabled
 };
 
 struct __attribute__((__packed__)) heap_big_write_t
@@ -84,6 +89,17 @@ struct __attribute__((__packed__)) heap_big_write_t
     uint32_t block_num;
 };
 
+struct __attribute__((__packed__)) heap_big_intent_t
+{
+    heap_entry_t hdr;
+
+    uint32_t block_num;
+    uint32_t offset;
+    uint32_t len;
+
+    // Also includes 2 bitmaps and 1 crc32c if checksums are disabled
+};
+
 struct __attribute__((__packed__)) heap_list_item_t
 {
     heap_list_item_t *prev;
@@ -137,7 +153,7 @@ class blockstore_heap_t
     uint8_t* buffer_area = NULL;
     int log_level = 0;
     const uint32_t meta_block_count = 0;
-    const uint32_t big_entry_size = 0;
+    const uint32_t max_entry_size = 0;
 
     robin_hood::unordered_flat_map<pool_id_t, pool_shard_settings_t> pool_shard_settings;
     // PG => inode => stripe => block number
@@ -229,6 +245,9 @@ public:
     // adds a big_write (overwrite) entry to an object
     int add_big_write(object_id oid, heap_entry_t *old_head, bool stable, uint64_t version,
         uint32_t offset, uint32_t len, uint64_t location, uint8_t *bitmap, uint8_t *data, uint32_t *modified_block);
+    // adds a big_intent (atomic partial modification) entry to an object
+    int add_big_intent(object_id oid, heap_entry_t *old_head, uint64_t version,
+        uint32_t offset, uint32_t len, uint8_t *bitmap, uint8_t *data, uint8_t *checksums, uint32_t *modified_block);
     // adds a compacted up to <version> entry to an object
     int add_compact(heap_entry_t *obj, uint64_t to_lsn, uint32_t *modified_block, uint8_t *new_csums);
     // "punch holes" in a big_entry and make a duplicate big_entry
@@ -293,6 +312,7 @@ public:
     heap_entry_t *prev(heap_entry_t *wr);
     uint32_t get_simple_entry_size();
     uint32_t get_big_entry_size();
+    uint32_t get_big_intent_entry_size();
     uint32_t get_small_entry_size(uint32_t offset, uint32_t len);
     uint32_t get_csum_size(heap_entry_t *wr);
     uint32_t get_csum_size(uint32_t entry_type, uint32_t offset = 0, uint32_t len = 0);
diff --git a/src/blockstore/blockstore_read.cpp b/src/blockstore/blockstore_read.cpp
index 9204c063..0126f77c 100644
--- a/src/blockstore/blockstore_read.cpp
+++ b/src/blockstore/blockstore_read.cpp
@@ -37,7 +37,9 @@ int blockstore_impl_t::dequeue_read(blockstore_op_t *op)
         }
         fulfilled += prepare_read(PRIV(op)->read_vec, obj, wr, op->offset, op->offset+op->len);
         if (fulfilled == op->len ||
-            wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_DELETE)
+            wr->type() == BS_HEAP_BIG_WRITE ||
+            wr->type() == BS_HEAP_BIG_INTENT ||
+            wr->type() == BS_HEAP_DELETE)
         {
             return false;
         }
@@ -110,7 +112,7 @@ int blockstore_impl_t::fulfill_read(blockstore_op_t *op)
 
 uint32_t blockstore_impl_t::prepare_read(std::vector<copy_buffer_t> & read_vec, heap_entry_t *obj, heap_entry_t *wr, uint32_t start, uint32_t end)
 {
-    if (wr->type() == BS_HEAP_BIG_WRITE)
+    if (wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_BIG_INTENT)
     {
         return prepare_read_with_bitmaps(read_vec, obj, wr, start, end);
     }
@@ -210,15 +212,18 @@ uint32_t blockstore_impl_t::prepare_read_simple(std::vector<copy_buffer_t> & rea
                 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)
+            if (!perfect_csum_update)
             {
-                for (auto owr = obj; owr && owr != wr; owr = heap->prev(owr))
+                if (wr->type() == BS_HEAP_BIG_INTENT && wr == obj &&
+                    wr->big_intent().offset < blk_end && wr->big_intent().offset+wr->big_intent().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;
-                    }
+                    skip_csum = COPY_BUF_SKIP_CSUM;
+                }
+                else if ((wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_BIG_INTENT) && wr != obj &&
+                    (obj->type() == BS_HEAP_INTENT_WRITE || obj->type() == BS_HEAP_SMALL_WRITE) &&
+                    obj->small().offset < blk_end && obj->small().offset+obj->small().len > blk_start)
+                {
+                    skip_csum = COPY_BUF_SKIP_CSUM;
                 }
             }
             if ((blk_end-1)/dsk.csum_block_size == blk_start/dsk.csum_block_size ||
@@ -266,8 +271,9 @@ void blockstore_impl_t::prepare_disk_read(std::vector<copy_buffer_t> & read_vec,
     {
         loc = wr->small().location-wr->small().offset;
     }
-    else /*if (wr->type() == BS_HEAP_BIG_WRITE)*/
+    else
     {
+        assert(wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_BIG_INTENT);
         loc = wr->big_location(heap);
     }
     copy_buffer_t vec = {
@@ -394,7 +400,8 @@ 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->small().offset/dsk.csum_block_size)*(dsk.data_csum_type & 0xFF)));
+            - ((wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_BIG_INTENT)
+                ? 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 24c5f8a2..5098afe8 100644
--- a/src/blockstore/blockstore_write.cpp
+++ b/src/blockstore/blockstore_write.cpp
@@ -197,15 +197,29 @@ int blockstore_impl_t::dequeue_write(blockstore_op_t *op)
     {
         // Direct intent-write
         BS_SUBMIT_CHECK_SQES(1);
-        auto wr = obj;
-        while (wr && (wr->type() == BS_HEAP_INTENT_WRITE || wr->type() == BS_HEAP_COMMIT || wr->type() == BS_HEAP_ROLLBACK))
+        int res = 0;
+        if (dsk.csum_block_size <= dsk.bitmap_granularity &&
+            (obj->entry_type == (BS_HEAP_BIG_INTENT|BS_HEAP_STABLE) ||
+            obj->entry_type == (BS_HEAP_BIG_WRITE|BS_HEAP_STABLE)))
         {
-            wr = heap->prev(wr);
+            // Even more simplified BIG_INTENT writes
+            // FIXME: Support RMW mode for csum_block_size > bitmap_granularity
+            PRIV(op)->location = obj->big_location(heap);
+            res = heap->add_big_intent(op->oid, obj, op->version, op->offset, op->len, op->bitmap,
+                (uint8_t*)op->buf, NULL, &PRIV(op)->modified_block);
+        }
+        else
+        {
+            auto wr = obj;
+            while (wr && (wr->type() == BS_HEAP_INTENT_WRITE || wr->type() == BS_HEAP_COMMIT || wr->type() == BS_HEAP_ROLLBACK))
+            {
+                wr = heap->prev(wr);
+            }
+            assert(wr && (wr->type() == BS_HEAP_BIG_WRITE || wr->type() == BS_HEAP_BIG_INTENT));
+            PRIV(op)->location = wr->big_location(heap);
+            res = heap->add_small_write(op->oid, obj, (BS_HEAP_INTENT_WRITE | (op->opcode == BS_OP_WRITE_STABLE ? BS_HEAP_STABLE : 0)),
+                op->version, op->offset, op->len, 0, op->bitmap, (uint8_t*)op->buf, &PRIV(op)->modified_block);
         }
-        assert(wr && wr->type() == BS_HEAP_BIG_WRITE);
-        PRIV(op)->location = wr->big_location(heap);
-        int res = heap->add_small_write(op->oid, obj, (BS_HEAP_INTENT_WRITE | (op->opcode == BS_OP_WRITE_STABLE ? BS_HEAP_STABLE : 0)),
-            op->version, op->offset, op->len, 0, op->bitmap, (uint8_t*)op->buf, &PRIV(op)->modified_block);
         if (res == EAGAIN)
         {
             assert(heap->get_inflight_queue_size());
diff --git a/src/disk_tool/disk_simple_offsets.cpp b/src/disk_tool/disk_simple_offsets.cpp
index a51493f1..8ace9f97 100644
--- a/src/disk_tool/disk_simple_offsets.cpp
+++ b/src/disk_tool/disk_simple_offsets.cpp
@@ -132,7 +132,7 @@ void disk_tool_simple_offsets(json11::Json cfg, bool json_output)
     uint64_t meta_size;
     if (meta_format == BLOCKSTORE_META_FORMAT_HEAP)
     {
-        uint32_t min_object_size = sizeof(heap_big_write_t) + data_csum_size + 2*clean_entry_bitmap_size;
+        uint32_t min_object_size = sizeof(heap_big_intent_t) + (data_csum_size ? data_csum_size : 4) + 2*clean_entry_bitmap_size;
         double meta_reserve = cfg["meta_reserve"].number_value();
         if (!meta_reserve)
             meta_reserve = 1.5;
diff --git a/src/test/test_blockstore.cpp b/src/test/test_blockstore.cpp
index 29c4fc22..9eecf32d 100644
--- a/src/test/test_blockstore.cpp
+++ b/src/test/test_blockstore.cpp
@@ -515,6 +515,8 @@ static void test_padded_csum_parallel_read(bool perfect, uint32_t offset)
     free(op2.buf);
 }
 
+// FIXME Add a simple intent_write / big_intent test
+
 int main(int narg, char *args[])
 {
     test_simple();
diff --git a/src/test/test_heap.cpp b/src/test/test_heap.cpp
index c697857d..a9c59425 100644
--- a/src/test/test_heap.cpp
+++ b/src/test/test_heap.cpp
@@ -1095,7 +1095,8 @@ void test_full_alloc()
     assert(ENOSPC == _test_do_big_write(heap, dsk, 1, epb*4*0x20000, 1, epb*4*0x20000, true, 0, 0, buffer_area.data(), 0));
 
     // We can still do some more overwrites into 3 of 4 nearfull blocks
-    int rest_fit = (dsk.meta_block_size % big_write_size)/small_write_size * 4;
+    int rest_fit = (big_write_size + dsk.meta_block_size % big_write_size)/small_write_size +
+        (dsk.meta_block_size % big_write_size)/small_write_size * 2;
     for (int i = 0; i < rest_fit; i++)
     {
         _test_small_write(heap, dsk, 1, 1*0x20000, 5+i, 8192, 4096, (4*epb-1)*16384+3*4096+i*4096, true, buffer_area.data(), false, UINT32_MAX /*any block*/);