From: "mark" <dvlhntr@gmail.com>
To: <pgsql-performance@postgresql.org>
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>
In-Reply-To: <4E4C2FEB.5060301@2ndQuadrant.com>
Subject: Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
Date: Wed, 17 Aug 2011 18:35:29 -0600
Message-ID: <009f01cc5d3e$bc3bc150$34b343f0$@com>
MIME-Version: 1.0
Content-Type: text/plain;
	charset="us-ascii"
Content-Transfer-Encoding: 7bit
Thread-Index: AcxdIyadIiz8TZPtRVKDEjm7hLwYpAAGr+6Q
Content-Language: en-us


> -----Original Message-----
> From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-
> owner@postgresql.org] On Behalf Of Greg Smith
> Sent: Wednesday, August 17, 2011 3:18 PM
> To: pgsql-performance@postgresql.org
> Subject: Re: [PERFORM] Raid 5 vs Raid 10 Benchmarks Using bonnie++
> 
> 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.
> 

To clarify maybe for those new at using non-default mount options.

With XFS the mount option is nobarrier. With ext4 I think it is barrier=0

Someone please correct me if I am misleading people or otherwise mistaken.

-mark