From mboxrd@z Thu Jan  1 00:00:00 1970
From: NeilBrown <neilb@suse.de>
Subject: Re: Data scribbling for raid6 is wrong?
Date: Thu, 15 Dec 2011 15:27:23 +1100
Message-ID: <20111215152723.1d2bcca0@notabene.brown>
References: <CAAV8rnKoga_DM1qh28ZGEsJMZAKPYDZcVFfLBSH9kPNHysf7LQ@mail.gmail.com>
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To: Tao Guo <glorioustao@gmail.com>
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On Thu, 15 Dec 2011 11:15:42 +0800 Tao Guo <glorioustao@gmail.com> wrote:

> Hi all,
>=20
> Today I checked the raid6's scribbling code, and I think there may be
> some improvements to handle bad sectors:

I think the common term is "scrubbing" rather than "scribbling".

>=20
> If we have one bad sector(with corrupted data) in the data block,
> scribbling thread will find parity mismatch and will try to
> recompute&rewrite P&Q, but that will cause final data loss.
> Since we have P & Q,=C2=A0 actually we can try to use them and find out t=
he
> wrong data block then fix it.
>=20
> But the algorithm to find the bad data block seems not
> straightforward... Does anyone know if there is any paper discussed
> this issue before?
>=20
> Update: I just found there is one talk about this in FAST08:
> http://www.usenix.org/events/fast08/tech/krioukov.html.
> But that approach will add checksums.etc. For bare-bones raid6, does
> any guru have any better ideas?

http://neil.brown.name/blog/20100211050355

NeilBrown

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