[Gluster-users] GlusterFS performance

Torbjørn Thorsen torbjorn at trollweb.no
Fri Mar 1 16:57:06 UTC 2013

Could it be possible that you are hitting only the cache on the first write ?
Maybe filling up a 512MB BBU cache on the server with the first write,
and then the next one comes and triggers a flush on the BBU ?

In any case, having output from a "gluster profile" that was active during
the writes is probably appreciated the people who can read them.

On Fri, Mar 1, 2013 at 12:42 PM, Nikita A Kardashin
<differentlocal at gmail.com> wrote:
> No, I am speaking about stranges in write to existing files. Maybe 'broken',
> but maybe root of trouble in my options (flush-behind or some else)?
> Illtustration of my situation:
> root at virtual:~# rm testfile.bin # removing old file
> root at virtual:~# dd if=/dev/zero of=testfile.bin bs=100M count=3 # testing
> speed on new file
> 3+0 records in
> 3+0 records out
> 314572800 bytes (315 MB) copied, 0.268943 s, 1.2 GB/s
> root at virtual:~# dd if=/dev/zero of=testfile.bin bs=100M count=3 # testing
> speed on existing file. WOW!
> 3+0 records in
> 3+0 records out
> 314572800 bytes (315 MB) copied, 290.361 s, 1.1 MB/s
> Why writing to existing file is soooooooooooooooo slooooooooooooow?
> 2013/3/1 Brian Candler <B.Candler at pobox.com>
>> On Fri, Mar 01, 2013 at 03:30:07PM +0600, Nikita A Kardashin wrote:
>> >    If I try to execute above command inside virtual machine (KVM), first
>> >    time all going right - about 900MB/s (cache effect, I think), but if
>> > I
>> >    run this test again on existing file - task (dd) hungs up and can be
>> >    stopped only by Ctrl+C.
>> >    Overall virtual system latency is poor too. For example, apt-get
>> >    upgrade upgrading system very, very slow, freezing on "Unpacking
>> >    replacement" and other io-related steps.
>> >    Does glusterfs have any tuning options, that can help me?
>> If you are finding that processes hang or freeze indefinitely, this is not
>> a question of "tuning", this is simply "broken".
>> Anyway, you're asking the wrong person - I'm currently in the process of
>> stripping out glusterfs, although I remain interested in the project.
>> I did find that KVM performed very poorly, but KVM was not my main
>> application and that's not why I'm abandoning it.  I'm stripping out
>> glusterfs primarily because it's not supportable in my environment,
>> because
>> there is no documentation on how to analyse and recover from failure
>> scenarios which can and do happen. This point in more detail:
>> http://www.gluster.org/pipermail/gluster-users/2013-January/035118.html
>> The other downside of gluster was its lack of flexibility, in particular
>> the
>> fact that there is no usage scaling factor on bricks, so that even with a
>> simple distributed setup all your bricks have to be the same size.  Also,
>> the object store feature which I wanted to use, has clearly had hardly any
>> testing (even the RPM packages don't install properly).
>> I *really* wanted to deploy gluster, because in principle I like the idea
>> of
>> a virtual distribution/replication system which sits on top of existing
>> local filesystems.  But for storage, I need something where operational
>> supportability is at the top of the pile.
>> Regards,
>> Brian.
> --
> With best regards,
> differentlocal (www.differentlocal.ru | differentlocal at gmail.com),
> System administrator.
> _______________________________________________
> Gluster-users mailing list
> Gluster-users at gluster.org
> http://supercolony.gluster.org/mailman/listinfo/gluster-users

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Torbjørn Thorsen
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