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Date: Mon, 30 Oct 2006 07:11:29 +0200
From: Petri Helenius <pete@he.iki.fi>
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To: Greg 'groggy' Lehey <grog@FreeBSD.org>
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Cc: Steve Peterson <stevep-hv@zpfe.com>, performance@freebsd.org
Subject: Re: gvinum raid5 performance seems slow
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Greg 'groggy' Lehey wrote:
>
> Single stream tests aren't very good examples for RAID-5, because it
> performs writes in two steps: first it reads the old data, then it
> writes the new data.
>   
If it really does it this way, instead doing write-only when writing 
sufficiently large blocks, that would explain the performance due to 
double rotational latency wait for each stripe size. Most 
implementations also use read/write caches to optimize this even further.

Pete