[lustre-discuss] Disaster recover files from ZFS OSTs

Hans Henrik Happe happe at nbi.dk
Sat Feb 16 15:05:53 PST 2019


Hi,

Moving a system away from Gluster to Lustre there is one feature we
miss. With Gluster the name space and data can easily be found on the
underlying filesystems. While we never needed it with Lustre, it would
be nice to have it as a last resort. Lustre has been rock solid, while
we have needed it plenty on Gluster.

Looking at the output of 'getstripe' I figured out how to find files
using the objids mod 128 (that's was how many dX dirs i found). Easy
with stripe-count=1, probably also with higher counts.

So given a backup of MDTs we should be able to do some poking around. We
could also do a database of getstripe info. Perhaps robinhood could help.

Is there some formal description of Lustre object layout? It seems
simple but I'm wondering if there are pitfalls. PFL seems to be pretty
well described.

Perhaps there are already tools for this, that we have missed?

Side note:

Looking at how Lustre put object files in large buckets, I was wondering
if this ZFS issue could become an issue:

https://github.com/zfsonlinux/zfs/issues/3967

Guess these buckets are rarely listed?

Cheers,
Hans Henrik


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