[Bugs] [Bug 1392419] New: High i/ o latency with random write workload from virtual machine(s)

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1392419

            Bug ID: 1392419
           Summary: High i/o latency with random write workload from
                    virtual machine(s)
           Product: Red Hat Gluster Storage
           Version: 3.2
         Component: replicate
          Keywords: Triaged
          Severity: medium
          Priority: medium
          Assignee: pkarampu at redhat.com
          Reporter: kdhananj at redhat.com
        QA Contact: nchilaka at redhat.com
                CC: bugs at gluster.org, mliyazud at redhat.com,
                    pcuzner at redhat.com, pkarampu at redhat.com,
                    rhs-bugs at redhat.com, storage-qa-internal at redhat.com
        Depends On: 1348068



+++ This bug was initially created as a clone of Bug #1348068 +++

Description of problem:
When using either a replica 3 or sharded replica 3 volume with virtual
machines, profiles that exhibit random writes cause high latencies than can
sometimes span several seconds.

This has been observed with both fio and iometer as load generators

Sequential writes do NOT exhibit this affect

Version-Release number of selected component (if applicable):


How reproducible:
Every time the workload is run this profile is observed


Steps to Reproduce:
1. use either an fio workload with random write or an iometer profile
(attached)
2. track the latency in the vm with pcp
3. 

Actual results:
High latencies are observed which could impact application response times

Expected results:
Spikes in random write workloads are accepted - may be in the 10's of
milliseconds - but latencies that are between 600ms 2s are a problem


Additional info:

--- Additional comment from Paul Cuzner on 2016-06-20 01:56 EDT ---

Added a screenshot showing the max latency observed from the iometer run. This
is from a single vm running the workload (as per the icf file attached to the
case)


Referenced Bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1348068
[Bug 1348068] High i/o latency with random write workload from virtual
machine(s)
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