Yes, it's related to this, most likely:
md0: echo current LBS to md/logical_block_size to prevent data loss issues
from LBS changes.
Note: After setting, array will not be assembled in old
kernels (<= 6.18)
So, if you create a new one it will have the md/logical_block_size already
set. Is there no warning when creating a new md array in 6.19?
On Sun, 15 Mar 2026 at 11:55, Steven Shiau <[email protected]>
wrote:
> Package: src:linux
> Version: 6.19.6+deb14-amd64
> Severity: important
>
> Description:
> We have identified a forward-compatibility regression in the md
> subsystem introduced between Linux Kernel 6.18 and 6.19. When creating a
> standard RAID 1 array using mdadm, the resulting superblock generated
> under Kernel 6.19 is violently rejected by older enterprise Linux
> kernels (e.g., older LTS kernels with version 6.1) with an -EINVAL
> argument error during assembly.
>
> A strict A/B test was performed using Debian Live (based on Sid)
> environments. The exact same version of mdadm (4.5-5) and the exact same
> creation command was used in both environments:
> mdadm --create "/dev/md127" --force --run --level=raid1 --raid-devices=2
> --metadata=1.2 --data-offset=34816 --bitmap=internal --assume-clean
> /dev/nvme0n1p2 /dev/nvme1n1p2
>
> Test 1 (Success):
> * Environment: Kernel 6.18.15+deb14-amd64
> * Result: Array creates successfully. When the machine reboots into the
> older guest OS, the legacy kernel assembles the array normally.
>
> Test 2 (Failure/Regression):
> * Environment: Kernel 6.19.6+deb14-amd64
> * Result: Array creates successfully in the live environment. However,
> when the machine reboots into the older guest OS, the legacy kernel
> rejects the component drives with:
> mdadm: failed to add /dev/nvme1n1p2 to /dev/md/0: Invalid argument.
> mdadm: failed to add /dev/nvme0n1p2 to /dev/md/0: Invalid argument.
> mdadm: /dev/md0 assembled from 0 drives
>
> Conclusion:
> Kernel 6.19 appears to be injecting a new feature flag, modifying the
> bitmap format, or altering the superblock structure during creation in a
> way that older md_mod drivers cannot parse, breaking backward
> compatibility for disaster recovery tools restoring older operating
> systems.
>
> Steven
>
--
Marcos R Carot
