[linux-lvm] Errors from a mirrored LV

[linux-lvm] Errors from a mirrored LV

[Fredrik Tolf]

Hi list,

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.

However, now that I still haven't got a new disk to replace it with, it
seems that LVM is nevertheless returning I/O errors for reads from the
broken sectors, as evidenced by logs like these:

ata4.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
ata4.00: BMDMA2 stat 0xc0009
ata4.00: cmd 25/00:08:a7:1c:84/00:00:27:00:00/e0 tag 0 dma 4096 in
         res 51/40:00:aa:1c:84/00:00:27:00:00/e0 Emask 0x9 (media error)
ata4.00: status: { DRDY ERR }
ata4.00: error: { UNC }
ata4.00: configured for UDMA/100
sd 3:0:0:0: [sdd] Result: hostbyte=DID_OK
driverbyte=DRIVER_SENSE,SUGGEST_OK
sd 3:0:0:0: [sdd] Sense Key : Medium Error [current] [descriptor]
Descriptor sense data with sense descriptors (in hex):
        72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00 
        27 84 1c aa 
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?

--

Fredrik Tolf

Re: [linux-lvm] Errors from a mirrored LV

[Stuart D Gathman]

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.