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Author Topic: RAID 5 Rescue How to ?  (Read 1298 times)

Offline keipou

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RAID 5 Rescue How to ?
« on: March 04, 2009, 07:44:39 AM »
I am new to linux world. I had 4 disks passed down to me and was told that they were RAID 5 configuration. Due to historical reason, I have to figure out the details and also extract the data from there.

I tried to boot up from Ubuntu Live CD and firstly, I tried

sudo fdisk -l /dev/sdx (for disk sda, sdb, sdc and sdd) and get

Device Boot Start End Blocks Id System
/dev/sdx1 1 48 385528+ 83 Linux
/dev/sdx2 49 65 136552+ 82 Linux swap / Solaris
/dev/sdx3 66 60772 487620946 83 Linux
/dev/sdx4 60772 60801 240974 83 Linux

I then read about in forum and finally after much struggle, I tried to reform the raid volume by :

sudo mdadm --create /dev/md3 --assume-clean --level=5 --verbose --raid-device=4 /dev/sdd3 /dev/sdc3 /dev/sdb3 /dev/sda3

I have to make some assumption on the disk order and guess most probably the data should be in /dev/sdx3

I got the prompt as :

mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 64K
mdadm: /dev/sdd3 appears to be part of a raid array:
level=raid5 devices=4 ctime=Tue Mar 3 06:48:25 2009
mdadm: /dev/sdc3 appears to be part of a raid array:
level=raid5 devices=4 ctime=Tue Mar 3 06:48:25 2009
mdadm: /dev/sdb3 appears to be part of a raid array:
level=raid5 devices=4 ctime=Tue Mar 3 06:48:25 2009
mdadm: /dev/sda3 appears to be part of a raid array:
level=raid5 devices=4 ctime=Tue Mar 3 06:48:25 2009
mdadm: size set to 487620864K
Continue creating array? y
mdadm: array /dev/md3 started.


So far so good. I then do

cat /proc/mdstat and get

md3 : active raid5 sda3[3] sdb3[2] sdc3[1] sdd3[0]
1462862592 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]

so I thought I should be on the way to get the data.

I do a mount

su do mount /dev/md3 /mnt

I have the error
mount: /dev/md3: can't read superblock

No matter how I tried the mount command, the error is persistent.

I then do

sudo mdadm --detail /dev/md3

Version : 00.90
Creation Time : Tue Mar 3 08:15:49 2009
Raid Level : raid5
Array Size : 1462862592 (1395.09 GiB 1497.97 GB)
Used Dev Size : 487620864 (465.03 GiB 499.32 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 3
Persistence : Superblock is persistent

Update Time : Tue Mar 3 08:19:05 2009
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 64K

UUID : 5430b403:a58267ca:e368bf24:bd0fce41 (local to host ubuntu)
Events : 0.2

Number Major Minor RaidDevice State
0 8 51 0 active sync /dev/sdd3
1 8 35 1 active sync /dev/sdc3
2 8 19 2 active sync /dev/sdb3
3 8 3 3 active sync /dev/sda3


That look good though.

I do sudo mdadm --examine /dev/md3

mdadm: No md superblock detected on /dev/md3.

Any idea how I could mount the array ? So far and yet so close.

Is the problem caused by wrong disk order ? If so, how do I find out the correct order ?

Any help or feedback is appreciated