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RE: Limited write bandwidth from ext3



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.

Thanks
Himanshu

-----Original Message-----
From: Keld Jørn Simonsen [mailto:keld dkuug dk] 
Sent: Wednesday, June 21, 2006 10:12 AM
To: Sinha, Himanshu
Cc: ext3-users redhat com
Subject: Re: Limited write bandwidth from ext3

On Mon, Jun 19, 2006 at 02:18:12PM -0400, Sinha_Himanshu 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
keld


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