[lustre-discuss] Issues regarding corss-version mounting of MDT

[Andreas Dilger]

On Feb 3, 2026, at 06:01, Huijun Wu <huijun18 at foxmail.com> wrote:
> I recently encountered an issue related to cross-version mounting of an MDT.
> After an MDS crash, I rebooted the MDS and accidentally mounted an MDT that was originally created and used with Lustre 2.15.4 using Lustre 2.16.1. After this, I noticed that many files and directories were shown as “????” on the client side.
> I then ran lfsck on this MDT, and found that some directories that originally belonged to this MDT disappeared entirely.
> Any recommendations on how to analyze, recover, or mitigate this issue?

There definitely shouldn't be any issues upgrading from a 2.15 MDT to a 2.16
MDT, and this is tested regularly during normal Lustre development.

Did you have any unusual features enabled in Lustre or ldiskfs?  Was the
filesystem originally formatted with 2.15, or was it formatted with an
older version and upgraded already?  Were there error messages on the MDS
or client console when accessing the problematic files?

Cheers, Andreas
---
Andreas Dilger
Principal Lustre Architect
adilger at thelustrecollective.com