[nzlug] LVM and toast....

[Nevyn]

On 4/2/07, Daniel Pittman <daniel at rimspace.net> wrote:
> Nevyn <nevynh at gmail.com> writes:
>
> > Nevermind - turns out that the raid device isn't starting as I'd hope.
> > It's showing 2 disks as spares. There was a command suggested in a few
> > places but they haven't helped at all.  mdadm --assemble --force
> >
> > The only other reference I found to try and fix this error said the
> > following: Rewrite the RAID superblocks by mkraid --force
> >
> > Unfortunately raidtools is no longer in Ubuntu.
>
> Anything that advises using raidtools is *bad* advice these days:
> mdadm will do anything they can do, better, faster, stronger, etc. ;)
>
> Anyhow: if the RAID was completely stopped and you ran 'mdadm --assemble
> --force' without effect there are two paths open to you:
>
> You could ask on the Linux RAID mailing list where Neil Brown is both
> active and helpful.  If this can be resolved you will not get a more
> authoritative answer.
>
>
> Secondly you could just get ... brutal about it: if you create a new
> RAID array with the same settings, components and device order as the
> first array everything will "just work."
>
> Of course, be warned: GET IT WRONG AND YOUR DATA IS TOAST! DEAD! GONE!
>
> Ahem.  Anyway: Linux software RAID uses the superblock at the end of the
> disk to manage devices -- there is nothing else it cares about.  So, the
> effect of this is to ignore the old superblock and create a new array
> with the existing data in place.
>
> NOTE: You may need to pass additional arguments to mdadm to prevent
> recalculation of parity blocks for RAID levels that use them.
>
>
> Anyway, once the new RAID array is in place and correct the data should
> be ready for you to fsck and go back to using as expected.
>
> Regards,
>         Daniel
>
> I would, personally, go for the mailing list option first. :)

Thanks Daniel. The second option though wouldn't be TOO bad except
trying to get the details just right. They're whole disk partitions
and everything so it's just a matter of getting the details right...
Device order I think is the one that I'm likely to trip up on - is the
device order the same as the order shown in /proc/mdstat?

Anyway, that's academic for the time being. I've subscribed to the
linux-raid list and so will get back to that option if I need it.
(Last ditch attempt)

Regards,
Nevyn.