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To: "Yeb Havinga" <yebhavinga@gmail.com>, "Greg Smith" <greg@2ndquadrant.com>
Cc: "Francisco Reyes" <lists@stringsutils.com>, "Pgsql performance"
	<pgsql-performance@postgresql.org>
Subject: Re: 10K vs 15k rpm for analytics
References: <cone.1267562557.293175.32557.1000@shelca>
	<4B8D7A6C.3010304@gmail.com> <4B8D7D18.9030407@2ndquadrant.com>
	<4B8E2664.80303@gmail.com>
Date: Wed, 03 Mar 2010 11:36:55 +0100
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From: "Pierre C" <lists@peufeu.com>
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In-Reply-To: <4B8E2664.80303@gmail.com>
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>>> With 24 drives it'll probably be the controller that is the limiting  
>>> factor of bandwidth. Our HP SAN controller with 28 15K drives delivers  
>>> 170MB/s at maximum with raid 0 and about 155MB/s with raid 1+0.

I get about 150-200 MB/s on .... a linux software RAID of 3 cheap Samsung  
SATA 1TB drives (which is my home multimedia server)...
IOPS would be of course horrendous, that's RAID-5, but that's not the  
point here.

For raw sequential throughput, dumb drives with dumb software raid can be  
pretty fast, IF each drive has a dedicated channel (SATA ensures this) and  
the controller is on a fast PCIexpress (in my case, chipset SATA  
controller).

I don't suggest you use software RAID with cheap consumer drives, just  
that any expensive setup that doesn't deliver MUCH more performance that  
is useful to you (ie in your case sequential IO) maybe isn't worth the  
extra price... There are many bottlenecks...