From: "David Lethe" <david@santools.com>
To: Ryan Wagoner <rswagoner@gmail.com>, Bill Davidsen <davidsen@tmr.com>
Cc: Alain Williams <addw@phcomp.co.uk>, linux-raid@vger.kernel.org
Subject: Re: High IO Wait with RAID 1
Date: Fri, 13 Mar 2009 13:02:00 -0500 [thread overview]
Message-ID: <407601c9a405$d3d76b6a$e90df40a@exchange.rackspace.com> (raw)
-----Original Message-----
From: "Ryan Wagoner" <rswagoner@gmail.com>
Subj: Re: High IO Wait with RAID 1
Date: Fri Mar 13, 2009 12:45 pm
Size: 2K
To: "Bill Davidsen" <davidsen@tmr.com>
cc: "Alain Williams" <addw@phcomp.co.uk>; "linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>
Yeah I understand the basics to RAID and the effect cache has on
performance. It just seems that RAID 1 should offer better write
performance than a 3 drive RAID 5 array. However I haven't run the
numbers so I could be wrong.
It could be just that I expect too much from RAID 1. I'm debating
about reloading the box with RAID 10 across 160GB of the 4 drives
(160GB and 320GB) and a mirror on the remaining space. In theory this
should gain me write performance.
Thanks,
Ryan
On Fri, Mar 13, 2009 at 11:22 AM, Bill Davidsen <davidsen@tmr.com> wrote:
> Ryan Wagoner wrote:
>>
>> I'm glad I'm not the only one experiencing the issue. Luckily the
>> issues on both my systems aren't as bad. I don't have any errors
>> showing in /var/log/messages on either system. I've been trying to
>> track down this issue for about a year now. I just recently my the
>> connection with RAID 1 and mdadm when copying data on the second
>> system.
>>
>> Unfortunately it looks like the fix is to avoid software RAID 1. I
>> prefer software RAID over hardware RAID on my home systems for the
>> flexibility it offers, especially since I can easily move the disks
>> between systems in the case of hardware failure.
>>
>> If I can find time to migrate the VMs, which run my web sites and
>> email to another machine, I'll reinstall the one system utilizing RAID
>> 1 on the LSI controller. It doesn't support RAID 5 so I'm hoping I can
>> just pass the remaining disks through.
>>
FYi - you can potentially get a big performance penalty when running a LSI raid card in jbod mode. The impact varies depending on a lot of things .. Try loading the jbod fimware on the card if it supports this and re run benchmarks
david
next reply other threads:[~2009-03-13 18:02 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-13 18:02 David Lethe [this message]
2009-03-13 18:29 ` High IO Wait with RAID 1 Ryan Wagoner
2009-03-13 22:10 ` David Rees
-- strict thread matches above, loose matches on Subject: below --
2009-03-12 23:46 Ryan Wagoner
2009-03-13 0:48 ` Alain Williams
2009-03-13 3:21 ` Ryan Wagoner
2009-03-13 9:39 ` Robin Hill
2009-03-13 10:17 ` Alain Williams
2009-03-13 16:22 ` Bill Davidsen
2009-03-13 17:42 ` Ryan Wagoner
2009-03-13 18:37 ` David Rees
2009-03-13 18:42 ` David Rees
2009-03-13 14:48 ` John Robinson
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