From: NeilBrown <neilb@suse.de>
To: David Brown <david.brown@hesbynett.no>
Cc: linux-raid@vger.kernel.org
Subject: Re: RAID6 r-m-w, op-journaled fs, SSDs
Date: Mon, 2 May 2011 08:01:31 +1000 [thread overview]
Message-ID: <20110502080131.02461482@notabene.brown> (raw)
In-Reply-To: <ipjtup$47u$1@dough.gmane.org>
On Sun, 01 May 2011 17:24:09 +0200 David Brown <david.brown@hesbynett.no>
wrote:
> On 01/05/11 00:27, NeilBrown wrote:
> > On Sat, 30 Apr 2011 16:27:48 +0100 pg_xf2@xf2.for.sabi.co.UK (Peter Grandi)
> > wrote:
> >
> >> * Can Linux MD do "abbreviated" read-modify-write RAID6
> >> updates like for RAID5? That is where not the whole stripe
> >> is read in, modified and written, but just the block to be
> >> updated and the parity wblocks.
> >
> > No. (patches welcome).
>
> As far as I understand the raid6 mathematics, it shouldn't be too hard
> to do such abbreviated updates, but that it could quickly lead to
> complex code if you are trying to update more than a couple of blocks at
> a time.
The RAID5 code already handle some of this complexity.
It would be quite easy to modify the code so that we have
- list of 'old' data blocks
- P and Q blocks
- list of 'new' data blocks.
We then just need to (optimised) maths to deduce the new P and Q given all
of that.
Of course you would only bother with a 7-or-more disk array..
NeilBrown
next prev parent reply other threads:[~2011-05-01 22:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-30 15:27 RAID6 r-m-w, op-journaled fs, SSDs Peter Grandi
2011-04-30 16:02 ` Emmanuel Florac
2011-04-30 22:27 ` NeilBrown
2011-05-01 15:24 ` David Brown
2011-05-01 16:48 ` Christoph Hellwig
2011-05-01 22:01 ` NeilBrown [this message]
2011-05-01 15:31 ` Peter Grandi
2011-05-01 18:32 ` David Brown
2012-01-12 10:33 ` pg_mh, Peter Grandi
2011-05-01 9:36 ` Dave Chinner
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