software raid5 degraded after power failure

[btkramer]

so, i 'm pretty new to ubuntu. i set up a home media server running 12.04 server, and setup a software raid5 array for it, following a tutorial. last night, there was a power failure, and when i tried to reboot i got a message saying the raid array was degraded. i booted anyways, and all my data is still there. i doubt that the drive actually failed. more likely it has become corrupted. although i do have a spare drive to replace it if needed.

how do i rebuild the array? i have found quite a few relevant posts, and have a basic idea how to proceed, but i could use some advice/direction.

what i have found out so far is that the array is mdp01, consisting of 4 drives, sda1-sdd1. the state of the array is listed as clean, degraded, and it seems that the drive sdb1 is the one with the problem, with its state listed as removed.

so, from what i can gather, i need to stop the array, and add the drive which has been removed back to the array and resync, but i can't seem to find out exactly how to do that.

thanks!

[darkod]

Post the outputs of these commands:

cat /proc/mdstat
sudo mdadm --examine /dev/sd[abcd]1

That should give us little more details.

[btkramer]

brian@Ubuntu-Server:~$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid5 sdd1[3] sda1[0] sdc1[2]
5860535808 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [U_UU]

unused devices: <none>
brian@Ubuntu-Server:~$ ^C
brian@Ubuntu-Server:~$ sudo mdadm --examine /dev/sd[abcd]1
[sudo] password for brian:
/dev/sda1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x0
Array UUID : 86ecabf5:ea889c14:26169875:c4bfdf8c
Name : Ubuntu-NAS:0
Creation Time : Fri Oct 5 21:32:19 2012
Raid Level : raid5
Raid Devices : 4

Avail Dev Size : 3907024896 (1863.01 GiB 2000.40 GB)
Array Size : 11721071616 (5589.04 GiB 6001.19 GB)
Used Dev Size : 3907023872 (1863.01 GiB 2000.40 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
State : clean
Device UUID : b7cf63a5:d093e89a:bfa44323:b9f4cdf5

Update Time : Sun Mar 31 18:50:48 2013
Checksum : 6ef26026 - correct
Events : 28467

Layout : left-symmetric
Chunk Size : 512K

Device Role : Active device 0
Array State : A.AA ('A' == active, '.' == missing)
/dev/sdb1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x0
Array UUID : 86ecabf5:ea889c14:26169875:c4bfdf8c
Name : Ubuntu-NAS:0
Creation Time : Fri Oct 5 21:32:19 2012
Raid Level : raid5
Raid Devices : 4

Avail Dev Size : 3907024896 (1863.01 GiB 2000.40 GB)
Array Size : 11721071616 (5589.04 GiB 6001.19 GB)
Used Dev Size : 3907023872 (1863.01 GiB 2000.40 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
State : clean
Device UUID : 4dc1f6de:a9f820e5:a7ca17c5:dc3f3eac

Update Time : Mon Mar 18 02:31:02 2013
Checksum : 4af2e24c - correct
Events : 64

Layout : left-symmetric
Chunk Size : 512K

Device Role : Active device 1
Array State : AAAA ('A' == active, '.' == missing)
/dev/sdc1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x0
Array UUID : 86ecabf5:ea889c14:26169875:c4bfdf8c
Name : Ubuntu-NAS:0
Creation Time : Fri Oct 5 21:32:19 2012
Raid Level : raid5
Raid Devices : 4

Avail Dev Size : 3907024896 (1863.01 GiB 2000.40 GB)
Array Size : 11721071616 (5589.04 GiB 6001.19 GB)
Used Dev Size : 3907023872 (1863.01 GiB 2000.40 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
State : clean
Device UUID : 9fde527f:4238b936:5f360b53:c6dac84a

Update Time : Sun Mar 31 18:50:48 2013
Checksum : 69748b46 - correct
Events : 28467

Layout : left-symmetric
Chunk Size : 512K

Device Role : Active device 2
Array State : A.AA ('A' == active, '.' == missing)
/dev/sdd1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x0
Array UUID : 86ecabf5:ea889c14:26169875:c4bfdf8c
Name : Ubuntu-NAS:0
Creation Time : Fri Oct 5 21:32:19 2012
Raid Level : raid5
Raid Devices : 4

Avail Dev Size : 3907024896 (1863.01 GiB 2000.40 GB)
Array Size : 11721071616 (5589.04 GiB 6001.19 GB)
Used Dev Size : 3907023872 (1863.01 GiB 2000.40 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
State : clean
Device UUID : ba87cbc8:a3eb76b0:39aeb5e4:076872d7

Update Time : Sun Mar 31 18:50:48 2013
Checksum : 4afeecc8 - correct
Events : 28467

Layout : left-symmetric
Chunk Size : 512K

Device Role : Active device 3
Array State : A.AA ('A' == active, '.' == missing)

[darkod]

Yeah, it looks like only sdb1 was dropped. I would zero the superblock on sdb1 to delete the old mdadm info, and add it to md0 again as new member:

sudo mdadm --zero-superblock /dev/sdb1
sudo mdadm --add /dev/md0 /dev/sdb1

After that let it sync fully, you can watch the sync process with cat /proc/mdstat. It might take a while.

After it's synced it should be fine.

[btkramer]

thanks!

do i need to stop the array first?

[darkod]

You shouldn't need to. Adding a disk can be done while the array is working, that's the point.

Usually you only stop the array to grow or reshape it.