[lustre-discuss] ZFS not freeing disk space

Alexander I Kulyavtsev aik at fnal.gov
Wed Aug 10 20:52:08 PDT 2016

"Deleting Files Doesn't Free Space"

"Deleting Files Doesn't Free Space, unless I unmount the filesystem"

There are more references listed on pages above.

Since 0.6.3 the possible work around can be to set zfs xattr=sa but that does not help with existing files on OST.

P.S. Apparently there's more than one way to leak the space.

On Aug 10, 2016, at 6:07 PM, Alexander I Kulyavtsev <aik at fnal.gov<mailto:aik at fnal.gov>> wrote:

It can be zfs snapshot holding space on ost.

Or, it can be zfs issue, zfs not releasing space until reboot. Check zfs bugs on zfs wiki.
Lustre shows change in OST used space right away.

zfs 0.6.3 is pretty old. We are using  with lustre 2.5.3. (there is  zfs
You may need to patch lustre 2.5.3 to go with some zfs 0.6.5.x;  patches were listed on this mail list.

On Aug 10, 2016, at 12:57 PM, Thomas Roth <t.roth at gsi.de<mailto:t.roth at gsi.de>> wrote:

Hi all,

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.

Checking the list of files I am currently using, I can verify that the migration is working: Lustre tells me that the top of the list is already on some other OSTs, the bottom of the list still resides on the OST in question.

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.

Is this a special feature of ZFS, or just a symptom of a broken OST?

I think I have seen this behavior before, and the "df" result shrank to an expected value after the server had been rebooted. In that case, this seems more like a too persistent caching effect -?


Thomas Roth
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