Date: Wed, 26 Jul 2000 10:32:44 +0930 From: Greg Lehey <grog@lemis.com> To: Meagan Jia Pi <meagan@e-lingo.com> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: a newbie RAID5 question Message-ID: <20000726103244.J55913@wantadilla.lemis.com> In-Reply-To: <07f601bff686$39112a20$e293c83f@meagan>; from meagan@e-lingo.com on Tue, Jul 25, 2000 at 03:18:12PM -0700 References: <07f601bff686$39112a20$e293c83f@meagan>
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On Tuesday, 25 July 2000 at 15:18:12 -0700, Meagan Jia Pi wrote:
> Hi All,
>
> I'd like to test single disk failure recovery a RAID5 system with
> FreeBSD installed. But I am not fully convinced that the test will
> be successful. I understand that parity is distributed among the
> drives, but how can a blank disk be recovered from the other disks?
Well, you can read from the array when one disk is missing, so all the
code needs to do is:
1. If the block to be replaced is a data block, read it from the
array and write it back to the drive.
2. If it's a parity block, read the band and create the parity from
it.
See /usr/src/sys/dev/vinum/vinumrevive.c, function revive_block, for
how this is implemented for Vinum.
Greg
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