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From: Malcolm Kay <malcolm.kay@internode.on.net>
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To: Andrea Venturoli <ml.ventu@flashnet.it>,
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Subject: Re: vinum and hot-swapping
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On Sun, 13 Jul 2003 19:15, 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?

Physical writes yes. But how does the data get there?
The SCSI bus (like any other) has a finite bandwidth.

But maybe if you are very clever you can coax the SCSI bus into
transmitting the same information to all disks in parallel.

> If so, why so much penalty?

Malcolm Kay