[Wylug-discuss] Help needed with 'failed' Linux software RAID 10

[Dave Fisher]

Hi Tim,

Thanks for replying, but I think you've been mislead by some
unecessary information from /proc/mdstat

md0 is a complete red herring ... an old array which was removed (and
partitions reformatted). It should no longer show up ... but does so,
because I forgot about an old spare which had dropped out.  ... just
ignore it

There is no md2.

There is only one RAID array. It is md1. It is arranged as RAID 10. It
consists essentially of 4 partitions (sd{f,g,h,i}4) plus a spare
(sdj4).

I don't know how the four partitions are paired.

Dave

On 1 June 2010 14:10, Tim Fletcher <tim at parrswood.manchester.sch.uk> wrote:
> On Sat, 2010-05-29 at 19:43 +0100, Dave Fisher wrote:
>
>> a) My, admittedly dodgy, understanding of RAID 10 is that if I can ID
>> the two halves of a pair, I should be able to mount the pair like
>> normal partitions or LVM volumes. Is this correct?
>
>> b) Is it possible to readonly mount the md1 partitions in their
>> current state - safely, without screwing-up further?
>
> Having read over this I'm not sure I fully understand how things where
> when they where working did you have:
>
> md0 raid1 (DiskA+DiskB)
> md1 raid1 (DiskA+DiskB)
> md2 raid0 (md0+md1)
>
> or did you have
>
> md0 raid0 (DiskA+DiskB)
> md1 raid0 (DiskA+DiskB)
> md2 raid1 (md0+md1)
>
> I think you had the former which means you need to tackle the problem in
> 2 layers, first of all you need to get at both parts of the RAID0 to
> spin up, that means 1 half of each of the raid1's
>
> You then need to get them to raid0 stripe together and that will give
> you your LVM2 volume group.
>
> Looking at the text attachment I think that sdf4+sdi4 and sdg4+sdh4 are
> the 2 mirror sets, this is judging by the event counters on them. Also I
> think that /dev/sdg4 has failed and maybe locked the sata bus.
>
> I would suggest trying
>
> Stopping the array altogether with:
> mdadm -S /dev/md1
>
> Telling mdadm to assemble the array by uuid but not start it if it's
> degraded with this command:
>
> mdadm -A /dev/md1 --no-degraded \
> --uuid=f4ddbd55:206c7f81:b855f41b:37d33d37
>
> There is the --force option that will force mdadm to update the
> superblocks and start the array that I have used to rescue me from a bad
> power failure on a raid6 array.
>
> --
> Tim Fletcher
> Learning Technologies Manager - Parrs Wood High School
>
>