Re: Do quota groups cost noticeable performance in 3.14?

[Duncan <1i5t5.duncan@cox.net>]

Marc MERLIN posted on Sun, 20 Apr 2014 12:59:01 -0700 as excerpted:

> I was looking at using qgroups for my backup server, which will be
> filled with millions of files in subvolumes with snapshots.
> 
> I read a warning that quota groups had performance issues, at least in
> the past.

Yes.  Additionally, there were serious bugs such that after subvolume 
deletes people would end up with negative quota usage!  Luckily I didn't 
need that for my use-case, but the recommendation for a couple kernels 
was definitely to avoid it for the time being, unless you were simply 
playing with it.  There were/are other filesystems with more mature quota 
solutions that actually work, if you're going to depend on it actually 
working.

> Is it still true?

Very good question.  Certainly both the qgroups bug reports and the 
patches have slowed down for 3.13/3.14 so it's gotta be better than it 
was, and while I don't use that feature and thus haven't been tracking it 
directly, I believe current status should be about where generic btrfs is 
at this point, that is, reasonably stable, but keep your backups tested 
and ready, just in case.

> If there is a performance issue, is it as simple as just turning off
> quota support and then things go back to normal?

IIRC yes, even back when the bugs were coming in right and left, that was 
basically the case -- WITH THE CAVEAT that back then anyway, a reboot was 
sometimes needed as the counts just weren't being updated correctly and 
people were getting some very weird results on deletion/disabling until 
reboot, sometimes.


Meanwhile, looking forward to your testing/reports/wiki-updates!  If you 
can do for qgroups what you've been doing for raid5/6 mode I'm sure a lot 
of folks (including me, I might not use it presently, but the better I 
understand it, the more effectively I can help others with questions) 
will be much edified. =:^)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman