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<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Hi Saisha,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Thanks for your interest in Lustre FS and research efforts.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Regarding your question. Had MDS been mounted when there was the xattre direct modification attempt?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">If yes, then xattr data consistency is not guaranteed.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">If it is possible, unmount MDS, make modifications, and mount it back.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">If MDS backend is LDISKFS, after unmounting MDS, you can mount it as
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Mount -t ldiskfs <path_to_dev> <mount_point> and modify any file.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">There is also debugfs utility which allows perform many useful modifications without mounting.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Best regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Artem Blagodarenko<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Best rega<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black">From:
</span></b><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black">lustre-devel
</span><a href="mailto:lustre-devel-bounces@lists.lustre.org"><span style="font-size:12.0pt;font-family:"Aptos",sans-serif">lustre-devel-bounces@lists.lustre.org</span></a><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black"> on behalf
of Saisha Kamat via lustre-devel </span><a href="mailto:lustre-devel@lists.lustre.org"><span style="font-size:12.0pt;font-family:"Aptos",sans-serif">lustre-devel@lists.lustre.org</span></a><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black"><br>
<b>Date: </b>Friday, 26 January 2024 at 19:58<br>
<b>To: </b></span><a href="mailto:lustre-devel@lists.lustre.org"><span style="font-size:12.0pt;font-family:"Aptos",sans-serif">lustre-devel@lists.lustre.org</span></a><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black">
</span><a href="mailto:lustre-devel@lists.lustre.org"><span style="font-size:12.0pt;font-family:"Aptos",sans-serif">lustre-devel@lists.lustre.org</span></a><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black"><br>
<b>Subject: </b>[lustre-devel] Direct Modification of Lustre Metadata on Disk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Hello,<br>
<br>
I am a Ph.D. student at UNC-Charlotte, focusing on research related to<br>
the Lustre File System. As part of my project, I am investigating<br>
scenarios involving the direct modification of xattr metadata on the<br>
Lustre disk, without unmounting the Lustre servers.<br>
<br>
To achieve this, I have attempted to open the MDS (Metadata Server)<br>
disk partition as a file descriptor, locate the target file and its<br>
xattr, and write a faulty value. However, I have encountered an<br>
unexpected issue where my changes appear to be saved to memory and are<br>
not being synchronized with the disk.<br>
After completing the write operation, when I read the same xattr<br>
again, it reflects the corrupted value. Strangely, when using the<br>
"getfattr" command, the original, correct value is displayed. This<br>
discrepancy has raised doubts about whether Lustre permits direct<br>
modifications to its metadata on the disk.<br>
Furthermore, I observed that even after unmounting and remounting the<br>
Lustre file system, the xattr continues to display the corrupted value<br>
upon reading, whereas "getfattr" still returns the original, correct<br>
value.<br>
<br>
Please help me understand whether Lustre allows direct modifications<br>
to its metadata on the disk and if there are any inherent limitations<br>
or considerations that I should be aware of.<br>
Additionally, any recommendations or alternative approaches for<br>
simulating faulty conditions for testing purposes would be highly<br>
valuable to my research.<br>
<br>
Thanks and Regards,<br>
Saisha<br>
_______________________________________________<br>
lustre-devel mailing list<br>
</span><a href="mailto:lustre-devel@lists.lustre.org"><span style="font-size:11.0pt">lustre-devel@lists.lustre.org</span></a><span style="font-size:11.0pt"><br>
</span><a href="http://lists.lustre.org/listinfo.cgi/lustre-devel-lustre.org"><span style="font-size:11.0pt">http://lists.lustre.org/listinfo.cgi/lustre-devel-lustre.org</span></a><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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