[Gluster-users] Diagnosing Intermittent Performance Problems Possibly Caused by Gremlins
justin at gluster.org
Tue Feb 3 10:58:07 UTC 2015
----- Original Message -----
> Hello List,
> So I've been frustraded by intermittent performance problems throughout
> January. The problem occurs on a two node setup running 3.4.5, 16 gigs
> of ram with a bunch of local disk. For sometimes an hour for sometimes
> weeks at a time (I have extensive graphs in OpenNMS) our Gluster boxes
> will get their CPUs pegged, and in vmstat they'll show extremely high
> numbers of context switches and interrupts. Eventually things calm
> down. During this time, memory usage actually drops. Overall usage on
> the box goes from between 6-10 gigs to right around 4 gigs, and stays
> there. That's what really puzzles me.
> When performance is problematic, sar shows one device, the device
> corresponding to the glusterfsd problem using all the CPU doing lots of
> little reads, Sometimes 70k/second, very small avg rq size, say 10-12.
> Afraid I don't have any saved output handy, but I can try to capture
> some next time it happens. I have tons of information frankly, but am
> trying to keep this reasonably brief.
> There are more than a dozen volumes on this two node setup. The CPU
> usage is pretty much entirely contained to one volume, a 1.5 TB volume
> that is just shy of 70% full. It stores uploaded files for a web app.
> What I hate about this app and so am always suspicious of, is that it
> stores a directory for every user in one level, so under the /data
> directory in the volume, there are 450,000 sub directories at this
> The only real mitigation step that's been taken so far was to turn off
> the self-heal daemon on the volume, as I thought maybe crawling that
> large directory was getting expensive. This doesn't seem to have done
> anything as the problem still occurs.
> At this point I figure there are one of two things sorts of things
> happening really broadly: one we're running into some sort of bug or
> performance problem with gluster we should either fix perhaps by
> upgrading or tuning around, or two, some process we're running but not
> aware of is hammering the file system causing problems.
> If it's the latter option, can anyone give me any tips on figuring out
> what might be hammering the system? I can use volume top to see what a
> brick is doing, but I can't figure out how to tell what clients are
> doing what.
> Apologies for the somewhat broad nature of the question, any input
> thoughts would be much appreciated. I can certainly provide more info
> about some things if it would help, but I've tried not to write a novel
Out of curiosity, are you able to test using GlusterFS 3.6.2? We've
had a bunch of pretty in-depth upstream testing at decent scale (100+
nodes) from 3.5.x onwards, with lots of performance issues identified
and fixed on the way through.
So, I'm kinda hopeful the problem you're describing is fixed in newer
Regards and best wishes,
GlusterFS - http://www.gluster.org
An open source, distributed file system scaling to several
petabytes, and handling thousands of clients.
My personal twitter: twitter.com/realjustinclift
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