[Gluster-users] GFS performance under heavy traffic

[David Cunningham]

Hi Raghavendra and Strahil,

We are using GFS version 5.6-1.el7 from the CentOS repository.
Unfortunately we can't modify the application and it expects to read and
write from a normal filesystem.

There's around 25GB of data being written during a business day, so over 10
hours that's around 0.7 MBps, which has me mystified as to how it can
generate 114MBps of network traffic. Granted we have read traffic as well,
but still. The chart shows much more inbound traffic to the GFS server than
outbound, suggesting the problem is with data writes.

Is it possible with GFS to not check with the other nodes when reading? Our
data is mostly static and we don't require 100% guarantee that the data is
up-to-date when reading.

Thanks for any assistance.


On Wed, 18 Dec 2019 at 16:39, Raghavendra Gowdappa <rgowdapp at redhat.com>
wrote:

> What version of Glusterfs are you using? Though, not sure what's the root
> cause of your problem, just wanted to point out a bug with read-ahead which
> would cause read-amplification over network [1][2], which should be fixed
> in recent versions.
>
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1214489
> [2] https://bugzilla.redhat.com/show_bug.cgi?id=1393419
>
> On Wed, Dec 18, 2019 at 2:50 AM David Cunningham <
> dcunningham at voisonics.com> wrote:
>
>> Hello,
>>
>> We switched a production system to using GFS instead of NFS at the
>> weekend, however it didn't go well on Monday when full load hit. The
>> application started crashing regularly and we had to revert to NFS. It
>> seems that the problem was high network traffic used by GFS.
>>
>> We've two GFS nodes plus one arbiter node, each about 1.3ms latency from
>> each other. Attached is a chart of network traffic on one of the GFS nodes.
>> We see that it saturated the 1Gbps link before we reverted to NFS at 15:10.
>>
>> The question is, why does GFS use so much network traffic and is there
>> anything we can do about it? NFS traffic doesn't exceed 4MBps, so 120MBps
>> for GFS seems awfully high.
>>
>> It would also be good to have faster read performance from GFS, but
>> that's another issue.
>>
>> Thanks in advance for any assistance.
>>
>> --
>> David Cunningham, Voisonics Limited
>> http://voisonics.com/
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-- 
David Cunningham, Voisonics Limited
http://voisonics.com/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782
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