From: Ogden <lists@darkstatic.com>
To: Greg Smith <greg@2ndquadrant.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
Date: Thu, 18 Aug 2011 12:31:28 -0500
Message-ID: <9D8C0F0D-0BAB-4531-8BDA-08D003E82F51@darkstatic.com> (raw)
In-Reply-To: <4E4C2FEB.5060301@2ndQuadrant.com>
References: <959BD2FA-0312-458B-BD5F-ED358D2C47ED@darkstatic.com>
<f4e06a7cad34ee9217a3e57fd4eb0e67.squirrel@sq.gransy.com>
<D89151D3-D2E5-47E3-8B90-4A573DAB5FFA@darkstatic.com>
<75A85649-2B95-43D5-8404-4776D2E580EC@darkstatic.com>
<4E4C2FEB.5060301@2ndQuadrant.com>
On Aug 17, 2011, at 4:17 PM, Greg Smith wrote:
> On 08/17/2011 02:26 PM, Ogden wrote:
>> I am using bonnie++ to benchmark our current Postgres system (on RAID 5) with the new one we have, which I have configured with RAID 10. The drives are the same (SAS 15K). I tried the new system with ext3 and then XFS but the results seem really outrageous as compared to the current system, or am I reading things wrong?
>>
>> The benchmark results are here:
>> http://malekkoheavyindustry.com/benchmark.html
>
> Congratulations--you're now qualified to be a member of the "RAID5 sucks" club. You can find other members at http://www.miracleas.com/BAARF/BAARF2.html Reasonable read speeds and just terrible write ones are expected if that's on your old hardware. Your new results are what I would expect from the hardware you've described.
>
> The only thing that looks weird are your ext4 "Sequential Output - Block" results. They should be between the ext3 and the XFS results, not far lower than either. Normally this only comes from using a bad set of mount options. With a battery-backed write cache, you'd want to use "nobarrier" for example; if you didn't do that, that can crush output rates.
I have mounted the ext4 system with the nobarrier option:
/dev/sdb1 on /var/lib/pgsql type ext4 (rw,noatime,data=writeback,barrier=0,nobh,errors=remount-ro)
Yet the results show absolutely a decrease in performance in the ext4 "Sequential Output - Block" results:
http://malekkoheavyindustry.com/benchmark.html
However, the Random seeks is better, even more so than XFS...
Any thoughts as to why this is occurring?
Ogden
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To: pgsql-performance@postgresql.org
Cc: lists@darkstatic.com, greg@2ndquadrant.com
Subject: Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
In-Reply-To: <9D8C0F0D-0BAB-4531-8BDA-08D003E82F51@darkstatic.com>
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