From: NeilBrown <neilb@suse.de>
To: "Jakub Husák" <jakub@gooseman.cz>
Cc: 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 15:41:07 +1000 [thread overview]
Message-ID: <20120926154107.1568a115@notabene.brown> (raw)
In-Reply-To: <50628B39.90205@gooseman.cz>
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On Wed, 26 Sep 2012 06:57:29 +0200 Jakub Husák <jakub@gooseman.cz> wrote:
> On 25.9.2012 14:32, NeilBrown wrote:
> > On Tue, 25 Sep 2012 11:48:34 +0200 <jakub@gooseman.cz> wrote:
> >
> >>
> >> Would you please refer to some documentation that this behaviour is
> >> correct? I now tried to fail several disks in raid5, raid0 and raid10-near,
> >> in case of r0 and r10n, mdadm didn't even allow me to remove more disks
> >> than is sufficient to access all the data. In case of r5 I was able to fail
> >> 2 out of 3, but the array was correctly marked as FAILED and couldn't be
> >> accessed at all. I'd expect that behaviour even in my case of raid10-far. I
> >> can't even assmenble and run it with less than required count of disks.
> >>
> > Could you please be explicit about exactly how the behaviour that you think
> > of as "correct" would differ from the current behaviour? Because I cannot
> > really see what point you are making - I need a little help.
> >
> > Thanks,
> > NeilBrown
> I think that when two adjacent drives fail, or the array is being
> assembled with two adjacent drives missing, the status wouldn't be
> "clean, degraded", the array "running" and reporting some inaccessible
> blocks when you try to use it - as it happens in my case of R10F.
> Instead, the array status would be "FAILED " and won't be allowed to
> run. R0, R5, R10N behave in that manner (if i tested well), which I
> consider correct.
>
> The "degraded" status means, at lest for me, that the array is fully
> functional, only with limited redundancy.
> R10 with far2 layout and four disks can't be only "degraded" when any
> two disks are missing, unlike R10 near2 in some cases.
>
> If something is still not clear, please be patient, i'll try to squeeze
> maximum out of my torturous English ;)
>
> Thaks
Ahh.... I see it now.
There is a bug in the 'enough' function in mdadm and in drivers/md/raid10.c
It doesn't handle 'far' layouts properly.
I'll sort out some patches.
Thanks,
NeilBrown
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next prev parent reply other threads:[~2012-09-26 5:41 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 [this message]
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
[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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