Re: Advice configuring ServeRAID 8k for performance

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Dave Crooke <dcrooke(at)gmail(dot)com>
Cc: Kenneth Cox <kenstir(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Advice configuring ServeRAID 8k for performance
Date: 2010-08-05 23:24:02
Message-ID: AANLkTikAfTY9eAW14Wm_GW_jbXQz+nSqm9H9Zp8WYDZR@mail.gmail.com
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On Thu, Aug 5, 2010 at 5:13 PM, Dave Crooke <dcrooke(at)gmail(dot)com> wrote:
> Definitely switch to RAID-10 .... it's not merely that it's a fair bit
> faster on normal operations (less seek contention), it's **WAY** faster than
> any parity based RAID (RAID-2 through RAID-6) in degraded mode when you lose
> a disk and have to rebuild it. This is something many people don't test for,
> and then get bitten badly when they lose a drive under production loads.

Had a friend with a 600G x 5 disk RAID-5 and one drive died. It took
nearly 48 hours to rebuild the array.

> Use higher capacity drives if necessary to make your data fit in the number
> of spindles your controller supports ... the difference in cost is modest
> compared to an overall setup, especially with SATA. Make sure you still
> leave at least one hot spare!

Yeah, a lot of chassis hold an even number of drives, and I wind up
with 2 hot spares because of it.

> Parity RAID simply isn't suitable for database use .... anyone who claims
> otherwise either (a) doesn't understand the failure modes of RAID, or (b) is
> running in a situation where performance simply doesn't matter.

The only time it's acceptable is when you're running something like
low write volume report generation / batch processing, where you're
mostly sequentially reading and writing 100s of gigabytes at a time in
one or maybe two threads.

--
To understand recursion, one must first understand recursion.

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