[Lustre-discuss] poor ost write performance.

Wed Apr 20 05:58:51 PDT 2011

Its an issue with ext[34].  Take a look at
http://jira.whamcloud.com/browse/LU-15 for more details.

Jeremy

On Wed, Apr 20, 2011 at 8:28 AM, James Rose <James.Rose at framestore.com>wrote:

> Hi Kevin,
>
> Thanks for the suggestion.  I will try this out.
>
> For the moment it seems that it may be disk space related.  I have
> removed some data from the file system.  Performance returned to where I
> would expect it to be as space freed up (currently at 83% full).  Since
> free space I have seen two messages on an OSS where the number of
> threads is tuned to the amount of RAM in the host and six on an OSS that
> has the number of threads set higher than it should.  This is a much
> better situation than the steady stream I was experiencing last night.
> Maybe disabling the read cache will remove the last few.
>
> I am still very curious what the rapid small reads seen when writing are
> as this showed up while mounted ldiskfs so not doing regular lustre
> operations at all.
>
> Thanks again for your help,
>
> James.
>
>
> On Wed, 2011-04-20 at 08:48 -0300, Kevin Van Maren wrote:
> > First guess is the increased memory pressure caused by the Lustre 1.8
> > read cache.  Many times "slow" messages are caused by memory
> > allocatons taking a long time.
> >
> > You could try disabling the read cache and see if that clears up the
> > slow messages.
> >
> > Kevin
> >
> >
> > On Apr 20, 2011, at 4:29 AM, James Rose <James.Rose at framestore.com>
> > wrote:
> >
> > > Hi
> > >
> > > We have been experiencing degraded performance for a few days on a
> > > fresh install of lustre 1.8.5 (on RHEL5 using sun ext4 rpms).  The
> > > initial bulk load of the data will be fine but once in use for a
> > > while writes become very slow to individual ost.  This will block io
> > > for a few minutes and then carry on as normal.  The slow writes will
> > > then move to another ost.  This can be seen in iostat and many slow
> > > IO messages will be seen in the logs (example included)
> > >
> > > The osts are between 87 90 % full.  Not ideal but has not caused any
> > > issues running 1.6.7.2 on the same hardware.
> > >
> > > The osts are RAID6 on external raid chassis (Infortrend).  Each ost
> > > is 5.4T (small).  The server is Dual AMD (4 cores). 16G Ram. Qlogic
> > > FC HBA.
> > >
> > > I mounted the osts as ldiskfs and tried a few write tests.  These
> > > also show the same behaviour.
> > >
> > > While the write operation is blocked there will be hundreds of read
> > > tps and a very small kb/s read from the raid but now writes.  As
> > > soon as this completes writes will go through at a more expected
> > > speed.
> > >
> > > Any idea what is going on?
> > >
> > > Many thanks
> > >
> > > James.
> > >
> > > Example error messages:
> > >
> > > Apr 20 04:53:04 oss5r-mgmt kernel: LustreError: dumping log to /tmp/
> > > lustre-log.1303271584.3935
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow quota
> > > init 286s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow journal
> > > start 39s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 39 previous
> > > similar messages
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow
> > > brw_start 39s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 38 previous
> > > similar messages
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow journal
> > > start 133s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 44 previous
> > > similar messages
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow
> > > brw_start 133s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 44 previous
> > > similar messages
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow journal
> > > start 236s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow i_mutex
> > > 40s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 2 previous
> > > similar messages
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 6 previous
> > > similar messages
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow i_mutex
> > > 277s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow
> > > direct_io 286s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 3 previous
> > > similar messages
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow journal
> > > start 285s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 1 previous
> > > similar message
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow
> > > commitrw commit 285s due to heavy IO load
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: Skipped 1 previous
> > > similar message
> > > Apr 20 04:53:40 oss5r-mgmt kernel: Lustre: rho-OST0012: slow parent
> > > lock 236s due to heavy IO load
> > >
> > >
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