[Wylug-help] Inactive RAID 10 Array

[Dave Fisher]

On Tue, Apr 14, 2009 at 11:58:15PM +0100, Chris Davies wrote:
> Using dd for each partition of the array will work. The MD superblock is 
> usually stored at the end of each physical partition (not sure how big 
> it is, though).

Thanks for that. With 5x 1TB disks to dd, it's going to take a while, but
it looks like I should have complete images of all 5 disks by teatime
tomorrow.

And from what you and John Hodrien say, these images may actually be
useful, if only in a 'belt and braces' sense.

> Have you considered simply trying to re-assemble the array?

Yes, but I've heard enough horror stories about people incorrectly
identifying the relevant partitions, to want a reasonable fallback
option.

As I implied in the original post, most of the data is unimportant, but
a tiny part of it could get me in me in very hot water with HMRC  ...
and I am not too proud to admit that the prospect scares me.

> 
> If you "mdadm --examine --scan -v", and the superblocks are still 
> intact, you'll get a dump of something like this (from my RAID 1 setup):
> 
> # mdadm --examine --scan -v
> ARRAY /dev/md1 level=raid1 num-devices=2 UUID=...
>     devices=/dev/hdc1,/dev/hda1
> ARRAY /dev/md5 level=raid1 num-devices=2 UUID=...
>     devices=/dev/hdc5,/dev/hda5
> ARRAY /dev/md6 level=raid0 num-devices=2 UUID=...
>     devices=/dev/hdc6,/dev/hda6
> ARRAY /dev/md9 level=raid10 num-devices=4 UUID=...
>     devices=/dev/dm-8,/dev/dm-3,/dev/dm-2,/dev/dm-1

I do see something like that, in particular, your md9 looks like my
'broken' md0 ... pace the device names. 
> 
> If you see the right devices you should simply be able to restart the array:
> 
> # mdadm --assemble /dev/md1 /dev/sd{b,c,d,e,f}4

I might try that once the backups are complete and verified.

> Provided you don't use --force it will refuse the action if there are 
> too many errors in the devices.

Will that protect me against mistakenly confusing the spare partition
with one of the original members of the array?

Some of the outputs from mdadm -E that I posted earlier appeared to
identify one partition as 'faulty removed', but others say it's
absolutely fine ... I find that a bit scary.

If that wasn't scary enough, adding new disks has completely changed all
the /dev/sd* names ... although I should be able to find their UUIDs ...
if only I could remember the necessary incantation.

Anyway, thanks for all your help.

Despite the pressure from HMRC, and my own impulsiveness, I'm going to
try to take this very slowly, one step at a time.

Dae