[lustre-discuss] ZFS not freeing disk space

Bob Ball ball at umich.edu
Wed Aug 10 15:26:32 PDT 2016

It is my understanding that when you set the OST deactivated, they you 
also don't get updates on the used space either, as of some recent 
version of Lustre.  It has never been clear to me though if a simple 
re-activation is needed to run the logs, or if the reboot is required, 
once it is re-activated.


On 8/10/2016 1:57 PM, Thomas Roth 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 -?
> Cheers,
> Thomas

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