diff --git a/src/disk_tool/disk_tool.cpp b/src/disk_tool/disk_tool.cpp
index c5a4eab9..f98f2b5e 100644
--- a/src/disk_tool/disk_tool.cpp
+++ b/src/disk_tool/disk_tool.cpp
@@ -200,6 +200,7 @@ static const char *help_text =
     "    --device_size 0          Set device size\n"
     "    --format text            Result format: json, options, env, or text\n"
     "\n"
+    "Default I/O mode for commands involving disk I/O is O_DIRECT. If you don't want it, add --io cached.\n"
     "Use vitastor-disk --help <command> for command details or vitastor-disk --help --all for all details.\n"
 ;
 
diff --git a/src/disk_tool/disk_tool_journal.cpp b/src/disk_tool/disk_tool_journal.cpp
index 0b4d608b..275908d5 100644
--- a/src/disk_tool/disk_tool_journal.cpp
+++ b/src/disk_tool/disk_tool_journal.cpp
@@ -18,7 +18,7 @@ int disk_tool_t::dump_journal()
         printf("[\n");
     if (all)
     {
-        dsk.journal_fd = open(dsk.journal_device.c_str(), O_DIRECT|O_RDONLY);
+        dsk.journal_fd = open(dsk.journal_device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDONLY);
         if (dsk.journal_fd < 0)
         {
             fprintf(stderr, "Failed to open journal device %s: %s\n", dsk.journal_device.c_str(), strerror(errno));
@@ -121,7 +121,7 @@ int disk_tool_t::dump_journal()
 
 int disk_tool_t::process_journal(std::function<int(void*)> block_fn)
 {
-    dsk.journal_fd = open(dsk.journal_device.c_str(), O_DIRECT|O_RDONLY);
+    dsk.journal_fd = open(dsk.journal_device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDONLY);
     if (dsk.journal_fd < 0)
     {
         fprintf(stderr, "Failed to open journal device %s: %s\n", dsk.journal_device.c_str(), strerror(errno));
diff --git a/src/disk_tool/disk_tool_meta.cpp b/src/disk_tool/disk_tool_meta.cpp
index 74debae2..0fa9ff9a 100644
--- a/src/disk_tool/disk_tool_meta.cpp
+++ b/src/disk_tool/disk_tool_meta.cpp
@@ -14,7 +14,7 @@ int disk_tool_t::process_meta(std::function<void(blockstore_meta_header_v2_t *)>
         fprintf(stderr, "Invalid metadata block size: is not a multiple of %d\n", DIRECT_IO_ALIGNMENT);
         return 1;
     }
-    dsk.meta_fd = open(dsk.meta_device.c_str(), O_DIRECT|O_RDONLY);
+    dsk.meta_fd = open(dsk.meta_device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDONLY);
     if (dsk.meta_fd < 0)
     {
         fprintf(stderr, "Failed to open metadata device %s: %s\n", dsk.meta_device.c_str(), strerror(errno));
diff --git a/src/disk_tool/disk_tool_resize.cpp b/src/disk_tool/disk_tool_resize.cpp
index cc7bd0fa..60104967 100644
--- a/src/disk_tool/disk_tool_resize.cpp
+++ b/src/disk_tool/disk_tool_resize.cpp
@@ -257,7 +257,7 @@ int disk_tool_t::resize_copy_data()
         iodepth = 32;
     }
     ringloop = new ring_loop_t(iodepth < RINGLOOP_DEFAULT_SIZE ? RINGLOOP_DEFAULT_SIZE : iodepth);
-    dsk.data_fd = open(dsk.data_device.c_str(), O_DIRECT|O_RDWR);
+    dsk.data_fd = open(dsk.data_device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDWR);
     if (dsk.data_fd < 0)
     {
         fprintf(stderr, "Failed to open data device %s: %s\n", dsk.data_device.c_str(), strerror(errno));
@@ -452,7 +452,7 @@ int disk_tool_t::resize_rewrite_journal()
 
 int disk_tool_t::resize_write_new_journal()
 {
-    new_journal_fd = open(new_journal_device.c_str(), O_DIRECT|O_RDWR);
+    new_journal_fd = open(new_journal_device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDWR);
     if (new_journal_fd < 0)
     {
         fprintf(stderr, "Failed to open new journal device %s: %s\n", new_journal_device.c_str(), strerror(errno));
@@ -521,7 +521,7 @@ int disk_tool_t::resize_rewrite_meta()
 
 int disk_tool_t::resize_write_new_meta()
 {
-    new_meta_fd = open(new_meta_device.c_str(), O_DIRECT|O_RDWR);
+    new_meta_fd = open(new_meta_device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDWR);
     if (new_meta_fd < 0)
     {
         fprintf(stderr, "Failed to open new metadata device %s: %s\n", new_meta_device.c_str(), strerror(errno));
diff --git a/src/disk_tool/disk_tool_udev.cpp b/src/disk_tool/disk_tool_udev.cpp
index e1f7d4b5..701e125a 100644
--- a/src/disk_tool/disk_tool_udev.cpp
+++ b/src/disk_tool/disk_tool_udev.cpp
@@ -122,7 +122,7 @@ uint32_t disk_tool_t::write_osd_superblock(std::string device, json11::Json para
     sb->size = sb_size;
     memcpy(sb->json_data, json_data.c_str(), json_data.size());
     sb->crc32c = crc32c(0, &sb->size, sb->size - ((uint8_t*)&sb->size - buf));
-    int fd = open(device.c_str(), O_DIRECT|O_RDWR);
+    int fd = open(device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDWR);
     if (fd < 0)
     {
         fprintf(stderr, "Failed to open device %s: %s\n", device.c_str(), strerror(errno));
@@ -150,7 +150,7 @@ json11::Json disk_tool_t::read_osd_superblock(std::string device, bool expect_ex
     json11::Json osd_params;
     std::string json_err;
     std::string real_device, device_type, real_data, real_meta, real_journal;
-    int r, fd = open(device.c_str(), O_DIRECT|O_RDWR);
+    int r, fd = open(device.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDWR);
     if (fd < 0)
     {
         fprintf(stderr, "Failed to open device %s: %s\n", device.c_str(), strerror(errno));
@@ -385,7 +385,7 @@ int disk_tool_t::pre_exec_osd(std::string device)
 int disk_tool_t::clear_osd_superblock(const std::string & dev)
 {
     uint8_t *buf = (uint8_t*)memalign_or_die(MEM_ALIGNMENT, 4096);
-    int fd = -1, r = open(dev.c_str(), O_DIRECT|O_RDWR);
+    int fd = -1, r = open(dev.c_str(), (options["io"] == "cached" ? 0 : O_DIRECT) | O_RDWR);
     if (r >= 0)
     {
         fd = r;