Re: How to improve db performance with $7K?

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Jacques Caron <jc(at)directinfos(dot)com>
Cc: Alex Turner <armtuk(at)gmail(dot)com>, Greg Stark <gsstark(at)mit(dot)edu>, William Yu <wyu(at)talisys(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: How to improve db performance with $7K?
Date: 2005-04-18 18:24:14
Message-ID: 873btokkoh.fsf@stark.xeocode.com
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Jacques Caron <jc(at)directinfos(dot)com> writes:

> When writing:
> - in RAID 0, 1 drive
> - in RAID 1, RAID 0+1 or 1+0, 2 drives
> - in RAID 5, you need to read on all drives and write on 2.

Actually RAID 5 only really needs to read from two drives. The existing parity
block and the block you're replacing. It just xors the old block, the new
block, and the existing parity block to generate the new parity block.

--
greg

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