linux-kernel - Re: Performance problems with 3ware 9500S-4LP and 2.6.25-rc3

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Date:	Wed, 27 Feb 2008 14:55:52 -0500
From:	Chris Snook <csnook@...hat.com>
To:	Andre Noll <maan@...temlinux.org>
CC:	adam radford <aradford@...il.com>,
	Tony Battersby <tonyb@...ernetics.com>,
	Johannes Wörner 
	<johannes.woerner@...bingen.mpg.de>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Performance problems with 3ware 9500S-4LP and 2.6.25-rc3

Andre Noll wrote:
> On 13:33, Chris Snook wrote:
> 
>>> During the daily cron job that uses rsync to sync a 500G file system
>> >from another machine to the raid on the 3ware controller the load
>>> jumps up, and the machine becomes sluggish as hell. For example, an
>>> ssh login to that machine takes minutes to complete and ldap becomes
>>> unreliable while the rsync job is running. Even Nagios complains
>>> about the machine being down while rsync is running.
>> You're putting your box under astronomical load.  This is generally 
>> regarded as a bad idea, regardless of how well your storage controller 
>> is performing.
> 
> The machine becomes sluggish also when I write directly to the raid
> array. A simple
> 
> 	dd if=/dev/zero of=tmpfile
> 
> shouldn't push the load up to 4, right?

Actually, it's normal for pdflush to spawn up to 8 threads when you're 
dirtying memory faster than it can be written to disk.  Load going to 4 
is not abnormal.  ssh logins taking minutes is very abnormal.

>> Can you measure the single-threaded throughput (say, 
>> coping one huge file, and then syncing) to give us a baseline 
>> performance figure?
> 
> Single threaded throughput seems to be ok (140M/s). The problem is
> that the machine becomes unresponsive.

Does the machine become unresponsive during the single-threaded test, or 
only when doing the rsync?

	-- Chris
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