Message-ID: <4509A447.3000507@commandprompt.com>
Date: Thu, 14 Sep 2006 11:49:43 -0700
From: "Joshua D. Drake" <jd@commandprompt.com>
Organization: Command Prompt, Inc.
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To: "Craig A. James" <cjames@modgraph-usa.com>
CC: pgsql-performance@postgresql.org
Subject: Re: RAID 0 not as fast as expected
References: <450999EC.8070601@modgraph-usa.com>
In-Reply-To: <450999EC.8070601@modgraph-usa.com>
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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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