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Date: Sun, 13 Jul 2003 13:26:07 +0930
From: Greg 'groggy' Lehey <grog@FreeBSD.org>
To: Andrea Venturoli <ml.ventu@flashnet.it>
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Subject: Re: vinum and hot-swapping
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On Sunday, 13 July 2003 at  4:45:08 -0500, Andrea Venturoli wrote:
> ** Reply to note from "Greg 'groggy' Lehey" <grog@freebsd.org> Sat, 12 Jul 2003 17:13:29 +0930
>
>
>> The real performance penalty for RAID-5 is simply that writes require
>> so much I/O.  Expect 25% of the write performance of RAID-0.
>
> Ok, I must ask this:
> Shouldn't SCSI system allow paralell writes on different disks?

Yes, it does.

> If so, why so much penalty?

Take a look at the man page, section "Performance considerations".
It's too long to repeat here.

Greg
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