Limited write bandwidth from ext3
Keld Jørn Simonsen
keld at dkuug.dk
Wed Jun 21 16:53:00 UTC 2006
On Wed, Jun 21, 2006 at 10:24:32AM -0400, Sinha_Himanshu at emc.com wrote:
> I misspoke earlier - our data is from a RHEL 4U1 system - 2.6.9 kernel.
> We will try RHEL 4U3 soon. That will give us a later kernel.
You need to go to 2.6.17 to get the performance enhancements I was
talking about, and 2.6.17 is very new, released less than a week ago.
I would compile that kernel myself for the testing.
> -----Original Message-----
> From: Keld Jørn Simonsen [mailto:keld at dkuug.dk]
> Sent: Wednesday, June 21, 2006 10:12 AM
> To: Sinha, Himanshu
> Cc: ext3-users at redhat.com
> Subject: Re: Limited write bandwidth from ext3
> On Mon, Jun 19, 2006 at 02:18:12PM -0400, Sinha_Himanshu at emc.com wrote:
> > We are running a benchmark that does single threaded 512 KB writes to a
> > LUN on a CLARiiON storage array. The dual Xeon host (Dell 2650) with 4
> > GB of memory runs RHEL 4U3
> > We measured the write bandwidth for writes to the block device
> > corresponding to the lun (e.g. /dev/sdb), a file in an ext2 filesystem
> > and to a file in an ext3 file system.
> > Write b/w for 512 KB writes
> > Block device 312 MBps
> > Ext2 file 247 MBps
> > Ext3 file 130 MBps
> > We are looking for ways to improve the ext3 file write bandwidth.
> > Tracing of I/Os at the storage array shows that in the case of ext3
> > experiment, the workload does not keep the lun busy enough. Every 5
> > seconds there is an increase in I/O activity that lasts for 2-3 seconds.
> > The lun then has very low activity for 2-3 seconds. It appears that the
> > buffers at the host are flushed every 5 seconds and the flushing takes
> > 2-3 seconds. To maximize write bandwidth, we would like to be in a
> > situation where the buffers are flushed continuously to keep the lun
> > constanly busy.
> > That is what we see in the case of the ext2 file.
> > In the case of ext2 we also see the host do quite a few ver large writes
> > (up to 7784 KB).
> Hmm, is the new kernel 2.6.17 addressing such issues?
> I understand that the new multibuffered implementation of ext3
> may enhance the performance considerably.
> What kernel did you benchmark on?
> best regards
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