Re: faulty array member

[Tim Small <tim@seoss.co.uk>]

>> then copy those individual blocks (only) over from sda2 (e.g. using
>> dd).  Once sdb1 has no pending sectors left, you should then be able to
>> re-add sda2 back into md0.
>
> that is exactly what I was trying to do.. but as the two drives
> partitioning are not the same, I don't know how to find the
> corresponding blocks/sectors in the two drives.

Under later kernels, you can definitely do something like:

cat /sys/block/sda/sda2/start

to find what the offset is from the start of the drive for each partition.

>> I don't know what the bad-block remapping is like on the CentOS4 kernel,
>
> I believe in this case, the bad-block remapping is done by the
> hd firmware.. please correct me if I'm wrong.

Yes it is, but the remap is triggered by a write to the block, so when
it happens automatically due to md, the following has to happen:

md tries to read from a sector, the read fails, so md reads from the
other drive, and then writes that data back to the original drive


> By the way, why it is not possible to re-add /dev/sda2 into the raid?

You should be able to do that, but md would in that case start a rebuild
from the other drive (i.e. copy all blocks from the other drive), and as
there are currently pending sectors on that drive, the rebuild will fail
- so you have to eliminate those faulty sectors on the source drive first.

Tim.

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