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Re: dell versus hp

From: Jeff Trout <threshar(at)torgo(dot)978(dot)org>
To: Jeff Frost <jeff(at)frostconsultingllc(dot)com>
Cc: Merlin Moncure <mmoncure(at)gmail(dot)com>, Alan Hodgson <ahodgson(at)simkin(dot)ca>, pgsql-performance(at)postgresql(dot)org
Subject: Re: dell versus hp
Date: 2007-11-15 14:41:59
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Lists: pgsql-performance
On Nov 14, 2007, at 9:19 PM, Jeff Frost wrote:

> On an 8xRAID10 volume with the smaller Areca controller we were  
> seeing around 450 seeks/sec.

On our 6 disk raid10 on a 3ware 9550sx I'm able to get about 120 seek  
+ reads/sec per process, with an aggregate up to about 500 or so.   
The disks are rather pooey 7.5k sata2 disks.   I'd been having perf  
issues and I'd been wondering why my IO stats were low.. turns out it  
was going as fast as the disks or controller could go.  I even went  
so far as to write  a small tool to sort-of simulate a PG index scan  
to remove all that from the question.  It proved my theory - seq  
performance was murdering us.

This information led me to spend a pile of money on an MSA70 (HP) and  
a pile of 15k SAS disks.
While significantly more expensive, the perf gains were astounding.   
I have 8 disks in a raid6 (iirc, I had comprable numbers for R10, but  
the space/cost/performance wasn't worth it). I'm able to get about  
350-400tps, per process, with an aggregate somewhere in the 1000s. (I  
drove it up to 2000 before stopping during testing)

Wether the problem is the controller or the disks, I don't know. I  
just know what my numbers tell me.  (And the day we went live on the  
MSA a large number of our perf issues went away.  Although, now that  
the IO was plenty sufficient the CPU became the bottleneck! Its  
always something!)   The sata array performs remarkably well for a  
sequential read though.  Given our workload, we need the random perf  
much more than seq, but I can see the opposite being true in a  
warehouse workload.

btw, the tool I wrote is here

Jeff Trout <jeff(at)jefftrout(dot)com>

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