On Fri, 8 Apr 2011 02:59:52 -0700 (PDT) Gavin Flower <gavinflower@xxxxxxxxx>
wrote:
>
> --- On Fri, 8/4/11, NeilBrown <neilb@xxxxxxx> wrote:
>
> > From: NeilBrown <neilb@xxxxxxx>
> > Subject: Re: RAID6 data-check took almost 2 hours, clicking sounds, system unresponsive
> > To: "Gavin Flower" <gavinflower@xxxxxxxxx>
> > Cc: linux-raid@xxxxxxxxxxxxxxx
> > Date: Friday, 8 April, 2011, 21:34
> > On Thu, 7 Apr 2011 18:32:04 -0700
> > (PDT) Gavin Flower <gavinflower@xxxxxxxxx>
> > wrote:
> >
> > > Hi Neil,
> > >
> > > My original email may have been eaten: as it did not
> > appear on the list, nor did I get an error message
> > back. So perhaps there was a problem with the attached
> > files.
> > >
> > > I will resend the attachments one at a time in
> > separate emails.
> > >
> > >
> > > Cheers,
> > > Gavin
> > >
> > > [begin original]
> > > Hi Neil,
> > >
> > > Your help (or anybody else's) would be greatly
> > appreciated, yet again
> >
> > Hi Gavin,
> > it isn't clear to me what help you want.
> >
> > Obviously there is some sort of hardware issue - possible a
> > drive, possibly a
> > bus problem - I really don't know.
> >
> > Apart from that things look normal.
> >
> > What exactly did you want explained?
> >
> > NeilBrown
>
> I guess I was surprised that the RAID system appeared normal and that it did not register any errors. I was hoping to get an idea as to which drive was problematic.
sdc2 was reporting read error. md/raid6 computed the data from the other
devices and wrote it back to sdc2. This appeared to work so md/raid6 assumed
everything was fine again. It reported this:
Apr 7 08:42:08 saturn kernel: [210414.109880] md/raid:md1: read error corrected (8 sectors at 17195840 on sdc2)
but didn't fail anything.
>
> I get the feeling, from your reply, that this is not specifically a RAID problem, that it just happens to affect a RAID array.
No, it was clearly a disk-drive problem.
e.g.
Apr 7 14:42:12 saturn kernel: [231957.756023] ata3.00: failed command: READ FPDMA QUEUED
a READ command sent to a n 'ata' device failed. i.e. disk error.
>
> I had thought that the RAID system should have been able to give me better diagnostics, but possibly I am being (inadvertently) unreasonable!
Well.... it did tell you that it got a read error and corrected it.
>
> Not sure what the significance of this mismatch is, and what I should do about it.
> # cat /sys/block/md2/md/mismatch_cnt
> 28904
> #
I'm not sure if read errors end up counting as mismatches.. They seem to for
raid1. The raid6 code is more complex and I don't feel like decoding it
right now.
In terms of "what to do about it" - the first thing must be to fix sdc.
Maybe there is a loose cable or a broken cable. Maybe the device needs to be
replaced.
Once you have resolved that and are fairly sure yours drives are all working,
echo check > /sys/block/md2/md/sync_action
once that finishes mismatch_cnt should ideally be zero. If it isn't, try
echo repair > /sys/block/md2/md/sync_action
but only do that if you are confident that your devices are good.
This will result in the same mismatch_cnt. However a subsequent 'check'
should then show zero.
NeilBrown
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