diff --git a/src/blockstore_disk.cpp b/src/blockstore_disk.cpp
index 9a2373a5..0ea8a2e4 100644
--- a/src/blockstore_disk.cpp
+++ b/src/blockstore_disk.cpp
@@ -193,7 +193,23 @@ void blockstore_disk_t::calc_lengths(bool skip_meta_check)
     meta_len = (1 + (block_count - 1 + meta_block_size / clean_entry_size) / (meta_block_size / clean_entry_size)) * meta_block_size;
     if (!skip_meta_check && meta_area_size < meta_len)
     {
-        throw std::runtime_error("Metadata area is too small, need at least "+std::to_string(meta_len)+" bytes");
+        if (!data_csum_type && !meta_version)
+        {
+            uint64_t clean_entry_v0_size = sizeof(clean_disk_entry) + 2*clean_entry_bitmap_size;
+            uint64_t meta_v0_len = (1 + (block_count - 1 + meta_block_size / clean_entry_v0_size)
+                / (meta_block_size / clean_entry_v0_size)) * meta_block_size;
+            if (meta_area_size >= meta_v0_len)
+            {
+                // Old metadata fits.
+                clean_entry_size = clean_entry_v0_size;
+                meta_len = meta_v0_len;
+                meta_version = BLOCKSTORE_META_VERSION_V1;
+            }
+        }
+        if (meta_area_size < meta_len)
+        {
+            throw std::runtime_error("Metadata area is too small, need at least "+std::to_string(meta_len)+" bytes");
+        }
     }
     // requested journal size
     if (!skip_meta_check && cfg_journal_size > journal_len)
diff --git a/src/blockstore_disk.h b/src/blockstore_disk.h
index 67a50837..a9c9c364 100644
--- a/src/blockstore_disk.h
+++ b/src/blockstore_disk.h
@@ -33,7 +33,7 @@ struct blockstore_disk_t
     bool disable_flock = false;
 
     int meta_fd = -1, data_fd = -1, journal_fd = -1;
-    uint64_t meta_offset, meta_device_sect, meta_device_size, meta_len;
+    uint64_t meta_offset, meta_device_sect, meta_device_size, meta_len, meta_version = 0;
     uint64_t data_offset, data_device_sect, data_device_size, data_len;
     uint64_t journal_offset, journal_device_sect, journal_device_size, journal_len;
 
diff --git a/src/blockstore_flush.cpp b/src/blockstore_flush.cpp
index bc9bf20d..c01e4be7 100644
--- a/src/blockstore_flush.cpp
+++ b/src/blockstore_flush.cpp
@@ -665,9 +665,12 @@ void journal_flusher_co::update_metadata_entry()
         new_entry->version = cur.version;
         if (!bs->inmemory_meta)
             memcpy(&new_entry->bitmap, new_clean_bitmap, bs->dsk.clean_dyn_size);
-        // Calculate metadata entry checksum
-        uint32_t *new_entry_csum = (uint32_t*)((uint8_t*)new_entry + bs->dsk.clean_entry_size - 4);
-        *new_entry_csum = crc32c(0, new_entry, bs->dsk.clean_entry_size - 4);
+        if (bs->dsk.meta_version >= BLOCKSTORE_META_VERSION_V2)
+        {
+            // Calculate metadata entry checksum
+            uint32_t *new_entry_csum = (uint32_t*)((uint8_t*)new_entry + bs->dsk.clean_entry_size - 4);
+            *new_entry_csum = crc32c(0, new_entry, bs->dsk.clean_entry_size - 4);
+        }
     }
 }
 
@@ -807,9 +810,12 @@ bool journal_flusher_co::clear_incomplete_csum_block_bits(int wait_base)
             calc_block_checksums(new_data_csums, true);
             if (!bs->inmemory_meta)
                 memcpy(&new_entry->bitmap, new_clean_bitmap, bs->dsk.clean_dyn_size);
-            // calculate metadata entry checksum
-            uint32_t *new_entry_csum = (uint32_t*)((uint8_t*)new_entry + bs->dsk.clean_entry_size - 4);
-            *new_entry_csum = crc32c(0, new_entry, bs->dsk.clean_entry_size - 4);
+            if (bs->dsk.meta_version >= BLOCKSTORE_META_VERSION_V2)
+            {
+                // calculate metadata entry checksum
+                uint32_t *new_entry_csum = (uint32_t*)((uint8_t*)new_entry + bs->dsk.clean_entry_size - 4);
+                *new_entry_csum = crc32c(0, new_entry, bs->dsk.clean_entry_size - 4);
+            }
         }
         // Write and fsync the modified metadata entry
     resume_2:
@@ -1364,7 +1370,8 @@ bool journal_flusher_co::trim_journal(int wait_base)
                 .crc32 = 0,
                 .magic = JOURNAL_MAGIC,
                 .type = JE_START,
-                .size = sizeof(journal_entry_start),
+                .size = ((!bs->dsk.data_csum_type && ((journal_entry_start*)flusher->journal_superblock)->version == JOURNAL_VERSION_V1)
+                    ? (uint32_t)JE_START_V1_SIZE : (uint32_t)JE_START_V2_SIZE),
                 .reserved = 0,
                 .journal_start = new_trim_pos,
                 .version = JOURNAL_VERSION_V2,
diff --git a/src/blockstore_init.cpp b/src/blockstore_init.cpp
index 5eb81b75..c2175cdf 100644
--- a/src/blockstore_init.cpp
+++ b/src/blockstore_init.cpp
@@ -123,6 +123,14 @@ resume_1:
             );
             exit(1);
         }
+        if (bs->dsk.meta_version && bs->dsk.meta_version != hdr->version)
+        {
+            printf(
+                "Metadata format version is %lu on disk, but %lu is currently selected in OSD configuration.\n"
+                " Please upgrade using vitastor-disk.\n", hdr->version, bs->dsk.meta_version
+            );
+            exit(1);
+        }
         if (hdr->version == BLOCKSTORE_META_VERSION_V2)
         {
             uint32_t csum = hdr->header_csum;
@@ -133,12 +141,18 @@ resume_1:
                 exit(1);
             }
             hdr->header_csum = csum;
+            bs->dsk.meta_version = BLOCKSTORE_META_VERSION_V2;
         }
         else if (hdr->version == BLOCKSTORE_META_VERSION_V1)
         {
             hdr->data_csum_type = 0;
             hdr->csum_block_size = 0;
             hdr->header_csum = 0;
+            // Enable compatibility mode - entries without checksums
+            bs->dsk.clean_entry_size = sizeof(clean_disk_entry) + bs->dsk.clean_entry_bitmap_size*2;
+            bs->dsk.meta_len = (1 + (bs->dsk.block_count - 1 + bs->dsk.meta_block_size / bs->dsk.clean_entry_size)
+                / (bs->dsk.meta_block_size / bs->dsk.clean_entry_size)) * bs->dsk.meta_block_size;
+            bs->dsk.meta_version = BLOCKSTORE_META_VERSION_V1;
         }
         else if (hdr->version > BLOCKSTORE_META_VERSION_V2)
         {
@@ -156,10 +170,12 @@ resume_1:
         {
             printf(
                 "Configuration stored in metadata superblock"
-                " (meta_block_size=%u, data_block_size=%u, bitmap_granularity=%u)"
-                " differs from OSD configuration (%lu/%u/%lu).\n",
+                " (meta_block_size=%u, data_block_size=%u, bitmap_granularity=%u, data_csum_type=%u, csum_block_size=%u)"
+                " differs from OSD configuration (%lu/%u/%lu, %u/%u).\n",
                 hdr->meta_block_size, hdr->data_block_size, hdr->bitmap_granularity,
-                bs->dsk.meta_block_size, bs->dsk.data_block_size, bs->dsk.bitmap_granularity
+                hdr->data_csum_type, hdr->csum_block_size,
+                bs->dsk.meta_block_size, bs->dsk.data_block_size, bs->dsk.bitmap_granularity,
+                bs->dsk.data_csum_type, bs->dsk.csum_block_size
             );
             exit(1);
         }
@@ -310,12 +326,15 @@ bool blockstore_init_meta::handle_meta_block(uint8_t *buf, uint64_t entries_per_
         clean_disk_entry *entry = (clean_disk_entry*)(buf + i*bs->dsk.clean_entry_size);
         if (entry->oid.inode > 0)
         {
-            // Check entry crc32
-            uint32_t *entry_csum = (uint32_t*)((uint8_t*)entry + bs->dsk.clean_entry_size - 4);
-            if (*entry_csum != crc32c(0, entry, bs->dsk.clean_entry_size - 4))
+            if (bs->dsk.meta_version >= BLOCKSTORE_META_VERSION_V2)
             {
-                printf("Metadata entry %lu is corrupt (checksum mismatch), skipping\n", done_cnt+i);
-                continue;
+                // Check entry crc32
+                uint32_t *entry_csum = (uint32_t*)((uint8_t*)entry + bs->dsk.clean_entry_size - 4);
+                if (*entry_csum != crc32c(0, entry, bs->dsk.clean_entry_size - 4))
+                {
+                    printf("Metadata entry %lu is corrupt (checksum mismatch), skipping\n", done_cnt+i);
+                    continue;
+                }
             }
             if (!bs->inmemory_meta && bs->dsk.clean_entry_bitmap_size)
             {
@@ -536,13 +555,30 @@ resume_1:
             fprintf(stderr, "First entry of the journal is corrupt or unsupported\n");
             exit(1);
         }
-        if (je_start->size == JE_START_V0_SIZE || je_start->version != JOURNAL_VERSION_V2)
+        if (je_start->size == JE_START_V0_SIZE ||
+            (je_start->version != JOURNAL_VERSION_V1 || je_start->size != JE_START_V1_SIZE) &&
+            (je_start->version != JOURNAL_VERSION_V2 || je_start->size != JE_START_V2_SIZE))
         {
-            // FIXME: Support v1 too
             fprintf(
-                stderr, "The code only supports journal version %d, but it is %lu on disk."
+                stderr, "The code only supports journal versions 2 and 1, but it is %lu on disk."
                     " Please use vitastor-disk to rewrite the journal\n",
-                JOURNAL_VERSION_V2, je_start->size == JE_START_V0_SIZE ? 0 : je_start->version
+                je_start->size == JE_START_V0_SIZE ? 0 : je_start->version
+            );
+            exit(1);
+        }
+        if (je_start->version == JOURNAL_VERSION_V1)
+        {
+            je_start->data_csum_type = 0;
+            je_start->csum_block_size = 0;
+        }
+        if (je_start->data_csum_type != bs->dsk.data_csum_type ||
+            je_start->csum_block_size != bs->dsk.csum_block_size)
+        {
+            printf(
+                "Configuration stored in journal superblock (data_csum_type=%u, csum_block_size=%u)"
+                " differs from OSD configuration (%u/%u).\n",
+                je_start->data_csum_type, je_start->csum_block_size,
+                bs->dsk.data_csum_type, bs->dsk.csum_block_size
             );
             exit(1);
         }