[lustre-discuss] ZFS not freeing disk space

[Kilian Cavalotti]

Hi Thomas,

On Wed, Aug 10, 2016 at 10:57 AM, Thomas Roth <t.roth at gsi.de> wrote:
> one of our ((Lustre 2.5.3, ZFS 0.6.3) OSTs got filled up to >90%, so I
> deactivated it and am now migrating files off of that OST.
>
> But when I do either 'lfs df' or 'df' on the OSS, and don't see any change
> in terms of bytes, while the migrated files already sum up to several GB.

It's very likely because your OST is deactivated, ie. disconnected
from the MDS, and thus freed up space is not accounted for. When you
reactivate your OST, it will reconnect to the MDS, which will start
cleaning up orphan inodes (ie. inodes that still exist on the OST but
are not referenced by any file on the MDT anymore). You should see
messages like "lustre-OST0000: deleting orphan objects from
0x0:180570872 to 0x0:180570891" when this happens.

That's actually how it's supposed to work, but there are some
limitations in 2.5 that may require a restart of the MDS. See
https://jira.hpdd.intel.com/browse/LU-7012 for details.

And of course, as soon as you re-activate your OST, new files will be
created on it, so it may skew the counters the other way.
But AFAIK, it's not specific to ZFS at all.

Cheers,
-- 
Kilian