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Re: raid10 hard disk choice

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Matthew Wakeling <matthew(at)flymine(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: raid10 hard disk choice
Date: 2009-05-22 06:59:18
Message-ID: alpine.GSO.2.01.0905220255340.20560@westnet.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, 21 May 2009, Scott Marlowe wrote:

> But in a RAID-10 you aggreate pairs like RAID-0, so you could write
> 250(n/2) times per second on 15k where n=4 and 166(n/2) for 10k drives
> where n=8.  So 500 versus 664... ?  Or am I getting it wrong.

Adding more spindles doesn't improve the fact that the disks can only 
commit once per revolution.  WAL writes are way too fine grained for them 
to get split across stripes to improve the commit rate.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD

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