From: Joshua D. Drake <jd@commandprompt.com>
To: Craig A. James <cjames@modgraph-usa.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: RAID 0 not as fast as expected
Date: Thu, 14 Sep 2006 11:49:43 -0700
Message-ID: <4509A447.3000507@commandprompt.com> (raw)
In-Reply-To: <450999EC.8070601@modgraph-usa.com>
References: <450999EC.8070601@modgraph-usa.com>
Craig A. James wrote:
> I'm experiment with RAID, looking for an inexpensive way to boost
> performance. I bought 4 Seagate 7200.9 120 GB SATA drives and two SIIG
> dual-port SATA cards. (NB: I don't plan to run RAID 0 in production,
> probably RAID 10, so no need to comment on the failure rate of RAID 0.)
>
> I used this raw serial-speed test:
>
> time sh -c "dd if=/dev/zero of=./bigfile bs=8k count=1000000 && sync"
> (unmount/remount)
> time sh -c "dd if=./bigfile of=/dev/null bs=8k count=1000000 && sync"
>
> Which showed that the RAID 0 4-disk array was almost exactly twice as
> fast as each disk individually. I expected 4X performance for a 4-disk
> RAID 0. My suspicion is that each of these budget SATA cards is
I am assuming linux here, Linux software raid 0 is known not to be super
duper.
Secondly remember that there is overhead involved with using raid. The
direct correlation doesn't work.
Joshua D. Drake
>
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To: pgsql-performance@postgresql.org
Cc: jd@commandprompt.com, cjames@modgraph-usa.com
Subject: Re: RAID 0 not as fast as expected
In-Reply-To: <4509A447.3000507@commandprompt.com>
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