Re: RAID10 failure(s)

[NeilBrown <neilb@suse.de>]

On Mon, 14 Feb 2011 17:08:45 -0600 Mark Keisler <grimm26@gmail.com> wrote:

> On Mon, Feb 14, 2011 at 4:48 PM, NeilBrown <neilb@suse.de> wrote:
> > On Mon, 14 Feb 2011 14:33:03 -0600 Mark Keisler <grimm26@gmail.com> wrote:
> >
> >> Sorry for the double-post on the original.
> >> I realize that I also left out the fact that I rebooted since drive 0
> >> also reported a fault and mdadm won't start the array at all.  I'm not
> >> sure how to tell which members were the in two RAID0 groups.  I would
> >> think that if I have a RAID0 pair left from the RAID10, I should be
> >> able to recover somehow.  Not sure if that was drive 0 and 2, 1 and 3
> >> or 0 and 1, 2 and 3.
> >>
> >> Anyway, the drives do still show the correct array UUID when queried
> >> with mdadm -E, but they disagree about the state of the array:
> >> # mdadm -E /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 | grep 'Array State'
> >>    Array State : AAAA ('A' == active, '.' == missing)
> >>    Array State : .AAA ('A' == active, '.' == missing)
> >>    Array State : ..AA ('A' == active, '.' == missing)
> >>    Array State : ..AA ('A' == active, '.' == missing)
> >>
> >> sdc still shows a recovery offset, too:
> >>
> >> /dev/sdb1:
> >>     Data Offset : 2048 sectors
> >>    Super Offset : 8 sectors
> >> /dev/sdc1:
> >>     Data Offset : 2048 sectors
> >>    Super Offset : 8 sectors
> >> Recovery Offset : 2 sectors
> >> /dev/sdd1:
> >>     Data Offset : 2048 sectors
> >>    Super Offset : 8 sectors
> >> /dev/sde1:
> >>     Data Offset : 2048 sectors
> >>    Super Offset : 8 sectors
> >>
> >> I did some searching on the "READ FPDMA QUEUED" error message that my
> >> drive was reporting and have found that there seems to be a
> >> correlation between that and having AHCI (NCQ in particular) enabled.
> >> I've now set my BIOS back to Native IDE (which was the default anyway)
> >> instead of AHCI for the SATA setting.  I'm hoping that was the issue.
> >>
> >> Still wondering if there is some magic to be done to get at my data again :)
> >
> > No need for magic here .. but you better stand back, as
> >  I'm going to try ... Science.
> > (or is that Engineering...)
> >
> >  mdadm -S /dev/md0
> >  mdadm -C /dev/md0 -l10 -n4 -c256 missing /dev/sdc1 /dev/sdd1 /dev/sde1
> >  mdadm --wait /dev/md0
> >  mdadm /dev/md0 --add /dev/sdb1
> >
> > (but be really sure that the devices really are working before you try this).
> >
> > BTW, for a near=2, Raid-disks=4 arrangement, the first and second devices
> > contain the same data, and the third and fourth devices also container the
> > same data as each other (but obviously different to the first and second).
> >
> > NeilBrown
> >
> >
> Ah, that's the kind of info that I was looking for.  So, the third and
> fourth disks are a complete RAID0 set and the entire RAID10 should be
> able to rebuild from them if I replace the first two disks with new
> ones (hence being sure the devices are working)?  Or I need to hope
> the originals will hold up to a rebuild?

No.

third and fourth are like a RAID1 set, not a RAID0 set.

First and second are a RAID1 pair.  Third and fourth are a RAID1 pair.

First and third
first and fourth
second and third
second and fourth

can each be seen as a RAID0 pair which container all of the data.

NeilBrown



> 
> Thanks for the info, Neil, and all your work in FOSS :)

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