From: keld@keldix.com
To: John Robinson <john.robinson@yuiop.co.uk>
Cc: NeilBrown <neilb@suse.de>, Jakub Hus?k <jakub@gooseman.cz>,
Mikael Abrahamsson <swmike@swm.pp.se>,
linux-raid@vger.kernel.org
Subject: Re: bug: 4-disk md raid10 far2 can be assembled clean with only two disks, causing silent data corruption
Date: Wed, 26 Sep 2012 11:23:40 +0200 [thread overview]
Message-ID: <20120926092340.GA21935@www5.open-std.org> (raw)
In-Reply-To: <20120926090803.GA21499@www5.open-std.org>
On Wed, Sep 26, 2012 at 11:08:03AM +0200, keld@keldix.com wrote:
> On Wed, Sep 26, 2012 at 09:59:42AM +0100, John Robinson wrote:
> > On 26/09/2012 09:28, keld@keldix.com wrote:
> > [...]
> > >We have discussed earlier how to implement raid10,far that would mean
> > >better survival chances with more disks failing. This is not implemented
> > >yet.
> >
> > No, but even if/when it is, there will still be some combinations of two
> > discs that you cannot afford to lose. The layout change to try to
> > improve redundancy will not be generic, as it doesn't work for an odd
> > number of discs, so the existing layout would have to be retained as an
> > option.
>
> Well, at least for backward compatibility we need an option for the current layout.
>
> For odd number of disks, I do think we can improve the chances for more failing disks, as
> discussed earlier.
To sum up: for raid10,f2 with odd numbers of disks, you can have a group of 3 disks and then
the rest of the disks ordered in pairs. Thus one disk in each of the pairs and one
disk in the 3-group all could fail and the raid would still be functional.
This is almost the same improvement as for the even numbered raid10,f2.
The scheme is easily generalised to raids with more than 2 copies.
Best regards
Keld
next prev parent reply other threads:[~2012-09-26 9:23 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-24 13:37 bug: 4-disk md raid10 far2 can be assembled clean with only two disks, causing silent data corruption Jakub Husák
2012-09-25 4:19 ` NeilBrown
2012-09-25 5:00 ` Mikael Abrahamsson
2012-09-25 9:48 ` jakub
2012-09-25 11:14 ` keld
2012-09-25 11:47 ` John Robinson
2012-09-25 12:32 ` NeilBrown
[not found] ` <50628B39.90205@gooseman.cz>
2012-09-26 5:41 ` NeilBrown
2012-09-26 8:28 ` keld
2012-09-26 8:59 ` John Robinson
2012-09-26 9:08 ` keld
2012-09-26 9:23 ` keld [this message]
[not found] ` <5067F014.5020600@gooseman.cz>
2012-09-30 10:24 ` keld
[not found] <50601CED.1050607@gooseman.cz>
2012-09-24 8:46 ` bug: 4-disk md raid10 far2 can be assembled clean with only two disks, causing "silent" " Jakub Husák
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