Raid 10 not assembling mdadm assembled from 2 drives - not enough to start the array
 

Hi recently setup a raid 10 on a CentOS 5 Linux server and I am having some issues with the raid not starting

This is message I get when I try and start it

mdadm: /dev/md0 assembled from 2 drives - not enough to start the array

Below is the information I've collected about any help on how I can get the raid back up and going to I can get the data off of it would be awesome thank you.


sudo mdadm --examine --scan -v
ARRAY /dev/md0 level=raid10 num-devices=4 UUID=91c36708:a7cbb532:5b51dc92:ba008491
devices=/dev/sdd1,/dev/sdc1,/dev/sdb1,/dev/sda1

Personalities : [raid10]
md0 : inactive sda1[0] sdd1[3] sdc1[2] sdb1[1]
1250274304 blocks

unused devices: <none>

sudo mdadm --examine --scan -v

ARRAY /dev/md0 level=raid10 num-devices=4 UUID=91c36708:a7cbb532:5b51dc92:ba008491
devices=/dev/sdd1,/dev/sdc1,/dev/sdb1,/dev/sda1

# mdadm --examine /dev/sda1
/dev/sda1:
Magic : a92b4efc
Version : 0.90.00
UUID : 91c36708:a7cbb532:5b51dc92:ba008491
Creation Time : Sat Jan 29 23:13:15 2011
Raid Level : raid10
Used Dev Size : 312568576 (298.09 GiB 320.07 GB)
Array Size : 625137152 (596.18 GiB 640.14 GB)
Raid Devices : 4
Total Devices : 3
Preferred Minor : 0

Update Time : Sun Feb 20 04:07:50 2011
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 2
Spare Devices : 0
Checksum : a56346f4 - correct
Events : 726551

Layout : near=2
Chunk Size : 256K

Number Major Minor RaidDevice State
this 0 8 1 0 active sync /dev/sda1

0 0 8 1 0 active sync /dev/sda1
1 1 8 17 1 active sync /dev/sdb1
2 2 0 0 2 faulty removed
3 3 0 0 3 faulty removed


# mdadm --examine /dev/sdb1:
Magic : a92b4efc
Version : 0.90.00
UUID : 91c36708:a7cbb532:5b51dc92:ba008491
Creation Time : Sat Jan 29 23:13:15 2011
Raid Level : raid10
Used Dev Size : 312568576 (298.09 GiB 320.07 GB)
Array Size : 625137152 (596.18 GiB 640.14 GB)
Raid Devices : 4
Total Devices : 3
Preferred Minor : 0

Update Time : Sun Feb 20 04:07:50 2011
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 2
Spare Devices : 0
Checksum : a5634706 - correct
Events : 726551

Layout : near=2
Chunk Size : 256K

Number Major Minor RaidDevice State
this 1 8 17 1 active sync /dev/sdb1

0 0 8 1 0 active sync /dev/sda1
1 1 8 17 1 active sync /dev/sdb1
2 2 0 0 2 faulty removed
3 3 0 0 3 faulty removed
mdadm --examine /dev/sdc1
/dev/sdc1:
Magic : a92b4efc
Version : 0.90.00
UUID : 91c36708:a7cbb532:5b51dc92:ba008491
Creation Time : Sat Jan 29 23:13:15 2011
Raid Level : raid10
Used Dev Size : 312568576 (298.09 GiB 320.07 GB)
Array Size : 625137152 (596.18 GiB 640.14 GB)
Raid Devices : 4
Total Devices : 3
Preferred Minor : 0

Update Time : Sun Feb 20 04:06:16 2011
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 1
Spare Devices : 0
Checksum : a56e5cc1 - correct
Events : 726548

Layout : near=2
Chunk Size : 256K

Number Major Minor RaidDevice State
this 2 8 33 2 active sync /dev/sdc1

0 0 8 1 0 active sync /dev/sda1
1 1 8 17 1 active sync /dev/sdb1
2 2 8 33 2 active sync /dev/sdc1
3 3 0 0 3 faulty removed

mdadm --examine /dev/sdd1
/dev/sdd1:
Magic : a92b4efc
Version : 0.90.00
UUID : 91c36708:a7cbb532:5b51dc92:ba008491
Creation Time : Sat Jan 29 23:13:15 2011
Raid Level : raid10
Used Dev Size : 312568576 (298.09 GiB 320.07 GB)
Array Size : 625137152 (596.18 GiB 640.14 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 0

Update Time : Sat Jan 29 23:13:15 2011
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Checksum : a53c3cb8 - correct
Events : 3

Layout : near=2
Chunk Size : 256K

Number Major Minor RaidDevice State
this 3 8 49 3 active sync /dev/sdd1

0 0 8 1 0 active sync /dev/sda1
1 1 8 17 1 active sync /dev/sdb1
2 2 8 33 2 active sync /dev/sdc1
3 3 8 49 3 active sync /dev/sdd1

Right, RAID 10 means a pair of RAID 0 arrays consequently mirrored into RAID 1. That mode requires a minimum of four drives. You can either stripe (RAID 0) two drives or mirror them (RAID 1). Not both. Sorry.
If you replace the two that were removed with working disks of equal or greater capacity to the two that are still installed & working, the array should rebuild itself.