[lustre-discuss] quotacheck on a live fs (pre 2.4)

[Thomas Roth]

My guess is that the trouble is caused by the Bytes added or moved while the quotacheck-scan is running. That gives you an estimate of the size of the 
inaccuracy.

We gave the users/groups quota in the order of 100 - 1000 Terabytes. During quotacheck, people would not write more than a few Terabytes, so the 
effect is negligible. Comparison with 'du' results showed no dramatic deviation.

quotacheck can be painful for the MDS, though. So if you have to go through several 100 M files - that might be a point for a  quiescent system.

Regards,
Thomas

On 03/17/2016 04:38 PM, John White wrote:
> So in the lustre manual, it says:
> lfs quotacheck requires the file system to be quiescent (i.e. no modifying operations like write, truncate, create or delete should run
> concurrently). Failure to follow this caution may result in inaccurate user/group disk usage. Operations that do not change Lustre files (such as read or mount) are okay to run.
>
> With that understood, what sort of inaccuracies are introduced by a live filesystem (with writers) during a quotacheck?  We have a file system we desperately need to use the quota mechanisms to get even ballpark estimates of per-user usage.  A downtime is not really in the cards at the moment.  Further, the file system isn’t long for this world and will be blown away in a matter of months (we just need to make it that long).
>
> Will writers on the fs make the data absolutely useless or will it just make things… fuzzy?
>
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