8.04 md raid5 troubleshooting

[Marius Gedminas]

On Wed, Nov 09, 2011 at 05:40:37PM +0100, Reinhard Haller wrote:
> Am 09.11.2011 14:04, schrieb Marius Gedminas:
> >>What is the suggested way to get the array back working?
> >Connect the spare drive, partition it, use mdadm to hot-add it, wait
> >while it syncs in the background.
> 
> Does it make sense to create a RAID-1 with the spare drive and the
> "defective" drive to clone the boot partition (assuming the
> defective drive is responsive)?

Most disk failures I've seen are localized: you can't read the data from
one particular bit.  It so happened that the bit that couldn't be read
appeared in the middle of your RAID-5 partition (statistically likely,
since RAID takes most up of the disk's sectors).  So, no, I wouldn't
expect any issues accessing the old boot partition.

RAID-1 sounds like a good idea.  I'm not exactly sure how you can
convert an existing standalone partition into a RAID-1 array; you
probably need to shrink it first a bit to leave space for the RAID
metadata, which, I think, lives at the end?  

Worst case, create a new RAID-1 on the new disk and clone your /boot
contents with tar, update the UUID in /etc/fstab and reinstall GRUB.  I
don't think the /boot UUID is written into the initramfs so at least you
wouldn't need to regenerate those.  I think.

Marius Gedminas
-- 
Voodoo Programming:  Things programmers do that they know shouldn't work but
they try anyway, and which sometimes actually work, such as recompiling
everything.
-- Karl Lehenbauer
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