Hello list,
This is a repost - I sent it to linux-raid back in January, but you were
all still having holidays - or hangovers or anything.
I was wondering why "--assemble --force" didn't work for a particular
(failed) raid-device. I got it to work and the data is safe now, but the
question about the non-working assembly remains.
I was trying to resurrect an array from a Synology disk station. As
follows: raid5 array with 4 disks, one disk utterly broken
(click-clack-click), one disk thrown out of the array.
Please note, that I used dmsetup to create an overlay disk, so the
"/dev/mapper/diskXp5" actually points to a /dev/sdN5 which is the
original array; I'm trying to not harm the original data. Here is the
result of mdadm v3.2.5 running assemble+force:
~# mdadm --verbose --assemble --force /dev/md99 /dev/mapper/disk1p5
/dev/mapper/disk2p5 /dev/mapper/disk3p5
mdadm: looking for devices for /dev/md99
mdadm: /dev/mapper/disk1p5 is identified as a member of /dev/md99, slot
32768.
mdadm: /dev/mapper/disk2p5 is identified as a member of /dev/md99, slot 1.
mdadm: /dev/mapper/disk3p5 is identified as a member of /dev/md99, slot 2.
mdadm: ignoring /dev/mapper/disk2p5 as it reports /dev/mapper/disk1p5 as
failed
mdadm: ignoring /dev/mapper/disk3p5 as it reports /dev/mapper/disk1p5 as
failed
mdadm: No suitable drives found for /dev/md99
OK. http://permalink.gmane.org/gmane.linux.raid/45064 says I should use
mdadm 3.3+, and luckily I had v3.3.2 - 21st August lying around, so
there we go:
~# ./mdadm --verbose --assemble --force /dev/md99 /dev/mapper/disk1p5
/dev/mapper/disk2p5 /dev/mapper/disk3p5
mdadm: looking for devices for /dev/md99
mdadm: /dev/mapper/disk1p5 is identified as a member of /dev/md99, slot
32768.
mdadm: /dev/mapper/disk2p5 is identified as a member of /dev/md99, slot 1.
mdadm: /dev/mapper/disk3p5 is identified as a member of /dev/md99, slot 2.
mdadm: no uptodate device for slot 0 of /dev/md99
mdadm: added /dev/mapper/disk3p5 to /dev/md99 as 2
mdadm: no uptodate device for slot 6 of /dev/md99
mdadm: added /dev/mapper/disk2p5 to /dev/md99 as 1
mdadm: /dev/md99 assembled from 2 drives - not enough to start the array.
Hmm, that doesn't help us either. (Slight difference between the two
versions, 3.2.5 deploys a broken array named md99 - which you can stop
afterwards - and 3.3.2 seems to auto-remove the array after trying to
start it - not sure if I describe the inner workings correctly)
Disk1 reports:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x0
Array UUID : 8ad57063:cf592975:9fabcc2b:13922e19
Name : 2
Creation Time : Sun May 13 08:23:21 2012
Raid Level : raid5
Raid Devices : 4
Avail Dev Size : 1944057456 (927.00 GiB 995.36 GB)
Array Size : 2916086016 (2781.00 GiB 2986.07 GB)
Used Dev Size : 1944057344 (927.00 GiB 995.36 GB)
Data Offset : 272 sectors
Super Offset : 8 sectors
State : clean
Device UUID : 4ae571dc:3c458e25:d219b536:c8b9a50e
Update Time : Sun Dec 28 10:41:55 2014
Checksum : 9a35a9ae - correct
Events : 744446
Layout : left-symmetric
Chunk Size : 64K
Device Role : Active device 32768
Array State : .AA. ('A' == active, '.' == missing)
Disk2:
[...]
State : clean
Device UUID : b381cfd4:d2474cc4:e4c0ad21:8565b2a5
Update Time : Sun Dec 28 10:41:55 2014
Checksum : b3569b7e - correct
Events : 744446
Layout : left-symmetric
Chunk Size : 64K
Device Role : Active device 1
Array State : .AA. ('A' == active, '.' == missing)
Disk3:
[...]
State : clean
Device UUID : c00d4418:c8313607:fb3a2018:d267a693
Update Time : Sun Dec 28 10:41:55 2014
Checksum : 1e1b8de5 - correct
Events : 744446
Layout : left-symmetric
Chunk Size : 64K
Device Role : Active device 2
Array State : .AA. ('A' == active, '.' == missing)
So the "Active device 32768" seems to be the culprit here, is that correct?
What would be the correct way to reassemble this array?
I managed to get it *working* again by recreating it with:
./mdadm --create --assume-clean --data-offset=136 -e 1.2 --level=5
--bitmap=none --raid-devices=4 --chunk=64 /dev/md99 /dev/mapper/disk1p5
/dev/mapper/disk2p5 /dev/mapper/disk3p5 missing
... but that feels a bit rude.
So, is there a "proper" way to reassemble this array?
For the record: the original array was most likely created on the
Synology disk station itself, which currently contains mdadm - v2.6.7 (I
don't know if that is the version that created the array). Also, I'm not
sure about the kernel version that's running there, but /lib/modules
contains modules that have a string "vermagic=2.6.15 ARMv5 gcc-3.4"
inside, so that might be the kernel version that was running when things
went wrong.
Best regards,
Valentijn
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
