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 11:08:03 +0200 [thread overview]
Message-ID: <20120926090803.GA21499@www5.open-std.org> (raw)
In-Reply-To: <5062C3FE.7090906@yuiop.co.uk>
On Wed, Sep 26, 2012 at 09:59:42AM +0100, John Robinson wrote:
> On 26/09/2012 09:28, keld@keldix.com wrote:
> [...]
> >I also understand it now, I think. raid10,f2 with 4 disks cannot in the
> >current implementation
> >survive 2 failing disks.
>
> It can, but only two non-adjacent discs. With 4 drives sda-sdd, than
> means you can only lose both sda and sdc, or sdb and sdd.
Agree
> >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.
best regards
keld
next prev parent reply other threads:[~2012-09-26 9:08 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 [this message]
2012-09-26 9:23 ` keld
[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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