Re: [lustre-devel] [EXTERNAL] Re: Inquiry Regarding Checksum Support for Lustre Extended Attributes

Hello,

Thank you for your previous response.

I have a question regarding the integration of ext4 metadata checksumming
with Lustre. Specifically, I am interested in enabling metadata check
summing on a Lustre file system backed by ldiskfs.
For context, I have a Lustre filesystem on /dev/sda, which is formatted as
ldiskfs (MDS). I used the command *tune2fs -O metadata_csum /dev/sda *to
enable metadata checksumming. However, after enabling this feature, I am
unable to mount the Lustre filesystem (MDS node).
Could you please advise if there is a way to enable metadata check summing
on the underlying ext4 filesystem and successfully mount the Lustre MDS or
OSS nodes on the same device? Are there specific steps or configurations
required to achieve this?

Thank you for your assistance and time.

Thanks and regards,
Saisha

On Wed, Jun 12, 2024 at 6:27 PM Andreas Dilger <[email protected]>
wrote:

> [*Caution*: Email from External Sender. Do not click or open links or
> attachments unless you know this sender.]
>   On Jun 12, 2024, at 12:35, Saisha Kamat via lustre-devel <
> [email protected]> wrote:
>
>
> Hello,
>
> I hope this email finds you well.
>
> My name is Saisha, and I am currently pursuing my Ph.D. at UNC-Charlotte,
> with a focus on research related to the Lustre File System. As part of my
> project, I am exploring the possibility of utilizing checksums to verify
> Lustre extended attributes.
>
> My understanding is that the ext4 file system supports checksums for
> extended attributes (xattrs). However, I am interested in whether this
> functionality extends to Lustre as well.
>
>
> Yes, the ext4 (and ZFS) xattr values have checksums.  No, the xattr
> checksums are neither managed or verified by Lustre, and only come into
> effect when they are passed on to the backing filesystem.  Conceivably, it
> would be possible to have a checksum (e.g. crc32c) for the xattr values in
> the MDS_GETXATTR and MDS_SETXATTR RPCs, if this is something you are
> interested to contribute.
>
> This could probably be done by overloading one of the 32-bit fields in the
> mdt_body for getxattr, and one in mdt_rec_reint for setxattr, but there is
> also "opportunistic" xattr prefetching done in the lookup RPC, so that
> would need to be covered as well.
>
> Also, the checksum would also need to be kept with the xattrs in cache and
> verified on access, otherwise they could become corrupted in memory after
> the RPC processing had completed.
>
> Finally, there is no interface to specify or verify the xattr checksum in
> the syscall interface, so there can be no guarantee that the data supplied
> in the setxattr is correct, or remains correct after supplied to getxattr,
> but the window there is very small.
>
> Cheers, Andreas
>
> I would greatly appreciate it if you could provide some insights or direct
> me to relevant documentation on this matter. Any information or guidance
> you can offer would be invaluable to my research.
>
> Thank you very much for your time and assistance.
>
> Thanks and Regards,
> Saisha
> _______________________________________________
> lustre-devel mailing list
> [email protected]
> http://lists.lustre.org/listinfo.cgi/lustre-devel-lustre.org
>
>
> Cheers, Andreas
> --
> Andreas Dilger
> Lustre Principal Architect
> Whamcloud
>
>
>
>
>
>
>
>

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