How to successfully change blocksize of disk on Azure?

Question

Im trying to change blocksize on Azure disk, to store multiple small files:

sudo mkfs -t ext4 -b 1024 /dev/sdd

Warning: specified blocksize 1024 is less than device physical sectorsize 4096 Discarding device blocks: done Creating filesystem with 268435456 1k blocks and 16777216 inodes Filesystem UUID: ***************************** Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409, 663553, 1024001, 1990657, 2809857, 5120001, 5971969, 17915905, 19668993, 25600001, 53747713, 128000001, 137682945, 161243137

Allocating group tables: done Writing inode tables: done Creating journal (262144 blocks): done Writing superblocks and filesystem accounting information: done

Looks more or less ok, but when checked :

azureuser@***************:~$ sudo blockdev --getbsz /dev/sdd

4096

Any workaround ?

Answer 1

Hi ,

Thanks for reaching out to Microsoft Q&A.

You are facing an issue where Azure disks enforce a physical sector size of 4096 bytes, which overrides your attempt to set a smaller block size (1024 bytes). The problem is that Azure-managed disks are based on SSDs, and most modern SSDs use 4K sectors natively, which makes it difficult to force a smaller block size.

Workarounds & Solutions:

Use a Loopback Device with a Smaller Blocksize

Instead of formatting the disk directly, you can create a file-backed loop device that supports a 1024-byte block size

Consider XFS Instead of EXT4

If your goal is efficient storage of small files, XFS might be a better choice than EXT4 with a smaller block size, since it handles small files better due to its inode clustering.

Use Filesystem-Level Optimizations

If your goal is to store many small files efficiently, you can also tweak inode settings while formatting. This will optimize for smaller file sizes without changing the block size.

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