[lustre-discuss] Analog of ll_recover_lost_found_objs for MDS

Chris Hunter chuntera at gmail.com
Fri Jul 29 10:24:43 PDT 2016

The "lfsck" feature added in lustre 2.7 will attempt recovery of MDT
orphan file objects from lost+found. Although likely doesn't help you

You may wish to look at script attached to LU-5626
ll_fix_mdt_lost_found.sh. I was intended to scan e2fsck logs for
recovery of "FID in dirent" errors. Another tool ll_decode_linkea is
mentioned in LU-8289 to help recover MDT lost+found objects. I have not
tried either tool.

Since critical information is stored as extended attributes in MDT
files, even a partial backup (file-level) can be useful for recovery.
Lustre operations manual discusses using LVM snapshots for MDT backup.
(assuming you created your MDT as lvm in the beginning...)

good luck,
chris hunter
chuntera at gmail.com

> Hi James,
> I'm not aware of a ready-to use tool, but if you have captured the
> output of e2fsck you can use that as a basis for a script that puts
> the
> files back to their original location.
> e2fsck usually prints out the full path and the inode numbers of the
> files/directories which it moves to lost+found and there, they are
> named
> "#$inode" (which makes scripting a bit ugly, but if you properly
> escape
> the '#'-sign and do some magic with awk, perl or alike, you can
> transform the log to a shell script that moves your files back to the
> orignal path). I have done this once after a file system corruption
> after an upgrade from 1.8 to 2.4 (which contained an ugly bug when
> enabling the "FID in dirent" feature).
> The backup... well, it gives you the chance to go back to the state
> where you started *before* the e2fsck. That would be a chance to
> capture
> the output again, in case you did not store it (actually, you could do
> this offline, on a copy of the backup). Restoring the MDT out of the
> backup however is only useful as long as you did not go in production
> after the e2fsck. And as I said, you still have to "repair" the
> restored
> MDT (probably by doing the same steps as you already did on the live
> system), but a second chance is better than no chance to go back...
> The
> backup is also good to investigate what happened during the e2fsck (in
> case it did something weird) or to go in with e2fsdebug for manual
> investigations... (e.g. manually look up inode<->path relations).
> Martin
> On 07/26/2016 04:08 PM, jbellinger wrote:
> > Is there, or could there be, something analogous to the OST recovery
> > tool that works on the lost+found on the MDT?  e2fsck went berserk.
> >
> > We're running 2.5.3.
> >
> >
> > Thanks,
> > James Bellinger
> >
> > Yes, we have an older (therefore somewhat inconsistent) backup of
> the
> > mdt, so we should be able to recover most things, _in theory_.  In
> > practice -- we'd love to hear other people's experience about
> recovery
> > using an inconsistent backup.
> > _______________________________________________

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