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Subject: Re: [linux-lvm] Errors from a mirrored LV
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To: linux-lvm@redhat.com

On 09/11/2010 01:02 AM, Fredrik Tolf wrote:
> Having a disk that's going awry, I'm glad I've got the data in a
> mirrored LV so that I can replace it.
>
> sd 3:0:0:0: [sdd] Add. Sense: Unrecovered read error - auto reallocate
> failed
> end_request: I/O error, dev sdd, sector 662969514
> ata4: EH complete
> I/O error in filesystem ("dm-3") meta-data dev dm-3 block 0x27841ae8
> ("xfs_trans_read_buf") error 5 buf count 4096
>
> Note that last line of log, emitted by XFS.
>
> Shouldn't LVM, when a read fails in a mirror, try to fetch that data
> from the second disk instead?
>   
Correct me if I'm wrong, but LVM mirror support is still experimental
and doesn't do a lot of things.  If you need reliable mirroring now, use
the md driver for raid1, and add the /dev/md* devices as physical volumes.

In the meantime, you should probably remove the failing PV.

AIX is still the best LVM mirroring I've seen.  I know ZFS is great too,
but it is more tied to a specific filesystem.