On Mon, Aug 16, 2010 at 10:43 AM, Tim Small <tim@xxxxxxxxxxx> wrote:
> On 16/08/10 07:12, Nicolas Jungers wrote:
>>
>> On 08/16/2010 07:54 AM, Tor Arne Vestbø wrote:
>>>
>>> You mean you sdc and sde plus either sdb or sdd, depending on which
>>> one I think is more sane a this point?
>>
>> I'd try both. Do a ddrescue of the failing one and try that (with copy of
>> the others) and check what's coming out.
>
> As an alternative to using ddrescue, you could quickly prototype various
> arrangements (without writing anything to the drives) using a device-mapper
> copy-on-write mapping - I posted some details to the list a while back when
> I was trying to use this to reconstruct a hw raid array... Check the list
> archives for details.
Cool, here's what I tried:
Created spares files for each of the devices
dd if=/dev/zero of=sdb_cow bs=1 count=0 seek=2GB
Mapped that to a loop device
losetup /dev/loop1 sdb_cow
Then ran the following for each device:
cow_size=`blockdev --getsize /dev/sdb1`
chunk_size=64
echo "0 $cow_size snapshot /dev/sdb1 /dev/loop1 p $chunk_size" |
dmsetup create sdb1_cow
After these were created I tried the following:
# mdadm -v -C /dev/md0 -l5 -n4 /dev/mapper/sdb1_cow
/dev/mapper/sdc1_cow missing /dev/mapper/sde1_cow
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 64K
mdadm: /dev/mapper/sdb1_cow appears to be part of a raid array:
level=raid5 devices=4 ctime=Sun Mar 2 22:52:53 2008
mdadm: /dev/mapper/sdc1_cow appears to be part of a raid array:
level=raid5 devices=4 ctime=Sun Mar 2 22:52:53 2008
mdadm: /dev/mapper/sde1_cow appears to be part of a raid array:
level=raid5 devices=4 ctime=Sun Mar 2 22:52:53 2008
mdadm: size set to 732571904K
Continue creating array? Y
mdadm: array /dev/md0 started.
# mdadm --detail /dev/md0
/dev/md0:
Version : 00.90
Creation Time : Mon Aug 16 18:20:06 2010
Raid Level : raid5
Array Size : 2197715712 (2095.91 GiB 2250.46 GB)
Used Dev Size : 732571904 (698.64 GiB 750.15 GB)
Raid Devices : 4
Total Devices : 3
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Mon Aug 16 18:20:06 2010
State : clean, degraded
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
UUID : 916ceaa2:b877a3cc:3973abef:31f2d600 (local to host monstre)
Events : 0.1
Number Major Minor RaidDevice State
0 251 9 0 active sync /dev/block/251:9
1 251 10 1 active sync /dev/block/251:10
2 0 0 2 removed
3 251 12 3 active sync /dev/block/251:12
And I can now mount /dev/mapper/raid-home !
The question now is, what next? Should I start copying things off to a
backup, or run fsck first or something else to try to repair errors?
Or perhaps are the 2GB sparse files to small for anything like that?
Thanks!
Tor Arne
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