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

Sun Feb 8 04:29:02 UTC 2026

Andreas, thanks for your reply.

The MDTs were originally created using Lustre 2.15.4. In my case, I accidentally mounted one of the MDTs with Lustre 2.16.1. The system has two MDTs in total: one remained untouched by 2.16.1, while the other was mounted once with 2.16.1.

After that, I switched back to Lustre 2.15.4 and mounted both MDTs. At that point, some files and directories appeared as “????”. It seemed that some kind of inconsistency between the states of the two MDTs caused the issue.

Later, I mounted the second MDT (the one that had not been touched before) with 2.16.1 as well, and then switched back to 2.15.4 to mount both MDTs. After this, the problem was resolved.

I’m curious about what kinds of inconsistencies between the MDTs might have led to this behavior.

Thanks in advance for your insights.

Cheers，
Huijun

         Original

From: Andreas Dilger <adilger at thelustrecollective.com&gt;
Date: Feb 7, 2026 08:10
To: Huijun Wu <huijun18 at foxmail.com&gt;
Cc: lustre-discuss <
&gt;
Subject: Re: [lustre-discuss] Issues regarding corss-version mounting of MDT

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

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

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

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