[Bugs] [Bug 1358606] New: limited throughput with disperse volume over small number of bricks

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1358606

            Bug ID: 1358606
           Summary: limited throughput with disperse volume over small
                    number of bricks
           Product: GlusterFS
           Version: 3.8.0
         Component: disperse
          Severity: low
          Assignee: bugs at gluster.org
          Reporter: mpillai at redhat.com
                CC: bugs at gluster.org



Description of problem:

The test uses a 1x(4+2) disperse volume created on 6 servers, where each brick
is on a RAID-6 device capable of delivering high throughput. A simple iozone
write test reports low throughput.

However, when the volume is changed to 4x(4+2) by carving 4 bricks on each h/w
RAID device, the throughput improves significantly -- close to the network line
speed.

This indicates some inefficiencies within gluster that is limiting throughput
in the 1x(4+2) case.

Version-Release number of selected component (if applicable):
glusterfs*-3.8.0-1.el7.x86_64 (on both clients and servers)
RHEL 7.1 (clients)
RHEL 7.2 (servers)

How reproducible:
Consistently

Actual results:

command:
iozone -i 0 -w -+n -c -e -s 10g -r 64k -t 8 -F /mnt/glustervol/f{1..8}.ioz

result for 1x(4+2) volume:
throughput for  8 initial writers  =  268871.84 kB/sec

result for 4x(4+2) volume (identical h/w setup):
throughput for  8 initial writers  =  755955.41 kB/sec

Additional info:

>From gluster vol info:
<quote>
[...]
Options Reconfigured:
cluster.lookup-optimize: on
server.event-threads: 4
client.event-threads: 4
performance.client-io-threads: on
transport.address-family: inet
performance.readdir-ahead: on
</quote>

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