Performance of MD1220 on Perc H800 slower than MD1120 on Perc/6E

Marc Stephenson marc.stephenson at lithium.com
Tue Sep 28 12:21:43 CDT 2010


I wanted to update the list regarding this particular issue we had with MD1220's.

We found that certain drives Dell ships with their MD1220's have a cache problem when performing random reads and writes. The particular drives in question are Seagate ST9300603SS which is a 2.5 inch SAS drive. The problem appeared to us when we were benchmarking random IO with a utility called sysbench. We had an XFS filesystem built on top of an LVM across 16 drives in a RAID-10 configuration. We would consistently see 25MB/s of random IO, power cycle all of the equipment, and then consistently see 48MB/s of random IO. Power cycling again would then result in a completely different benchmark for random IO. We didn't observe any issues with sequential IO though. Eventually Dell recognized that there really was an issue with these drives and shipped us replacement MBD2300RC drives. Our problems have now gone away on both MD1220's.


________________________________
From: Blake Hudson <blake at ispn.net>
Date: Tue, 31 Aug 2010 15:22:14 -0700
To: <linux-poweredge at dell.com>
Subject: Re: Performance of MD1220 on Perc H800 slower than MD1120 on Perc/6E




________________________________
From: Richard Ems <richard.ems at cape-horn-eng.com>
 Date: Wed, 18 Aug 2010 03:11:12 -0700
 To: Marc Stephenson <marc.stephenson at lithium.com>
 Cc: <linux-poweredge at dell.com>
 Subject: Re: Performance of MD1220 on Perc H800 slower than MD1120 on Perc/6E

On 08/16/2010 09:59 PM, Marc Stephenson wrote:
> Their next recommendation was to try installing RHEL 5 which I'm working
> on now. Has anyone else seen performance problems on their MD1220's?

Hi Marc,

Any new performance values on RHEL 5 ?
Why are you using sysbench? Have you tried other tools?

We are getting a MD1200 and a H800 controller the next days, and I am
very interested in your results. We are going to use also XFS.

Your HDDs are 2.5", right? Aren't this drives slower than the 3.5" ones?

Best regards,
Richard


Just FYI, the only 2.5" 300GB drives I can spec a power vault with are 10k RPM, while the only 3.5" 300GB drives (currently) are 15k RPM. 15k > 10k. When it comes to rotating magnetic disk drives, faster rotation is better.

You can get 15k drives in the MD1220, but they're going to be smaller so you're going to need more if you want to keep the same capacity.

There's nothing intrinsically slower about a 2.5" drive - in fact, 15k 3.5" drives use platters sized between 2.5" and 3". However, there is room for more platters in a 3.5" drive. Which means that there are less compromises between high capacity and high speed - you can have both in the 3.5" form factor. 2.5" drives seem to be either high capacity or high speed, but not both.

--Blake

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