[lustre-devel] Direct Modification of Lustre Metadata on Disk

[Saisha Kamat]

Hello,

I am a Ph.D. student at UNC-Charlotte, focusing on research related to
the Lustre File System. As part of my project, I am investigating
scenarios involving the direct modification of xattr metadata on the
Lustre disk, without unmounting the Lustre servers.

To achieve this, I have attempted to open the MDS (Metadata Server)
disk partition as a file descriptor, locate the target file and its
xattr, and write a faulty value. However, I have encountered an
unexpected issue where my changes appear to be saved to memory and are
not being synchronized with the disk.
After completing the write operation, when I read the same xattr
again, it reflects the corrupted value. Strangely, when using the
"getfattr" command, the original, correct value is displayed. This
discrepancy has raised doubts about whether Lustre permits direct
modifications to its metadata on the disk.
Furthermore, I observed that even after unmounting and remounting the
Lustre file system, the xattr continues to display the corrupted value
upon reading, whereas "getfattr" still returns the original, correct
value.

Please help me understand whether Lustre allows direct modifications
to its metadata on the disk and if there are any inherent limitations
or considerations that I should be aware of.
Additionally, any recommendations or alternative approaches for
simulating faulty conditions for testing purposes would be highly
valuable to my research.

Thanks and Regards,
Saisha