I recently had a drive fail in a 3 drive RAID 5 array that had been up
for nearly 3 years. I've handled this several time before but this
time, whilst swapping out the failed drive, a 2nd drive dropped out of
the array for some reason and when I tried to add it back, became
marked as a spare. I haven't done anything with the new drive yet so
whenever I try to start the array, I get one active drive and one
spare and hence the array can't start. I can't work out how to prevent
the 2nd drive being detected as a spare and allow the array to start
with 2 of 3 drives. As far as I can tell from using --examine, the
event counts are identical so I'm hoping recovery is feasible.
Unfortunately I don't know what order the disks were originally in
(all of the original disks have failed and been replaced during the
array's life so far).
So, 2 questions: Is there a simple way to stop the 2nd drive thinking
that it's a spare so I can just assemble the array. If not, I believe
I should be able to recreate the array with --assume-clean: How do I
determine the correct order for the drives? (If it's a matter of trial
and error, how do I know when I get it right?)
The output from --examine on the two drives is:
/dev/sdb2:
Magic : a92b4efc
Version : 0.90.00
UUID : cd57d356:c19317bf:a7df5645:f34ebdb2
Creation Time : Fri Mar 20 17:53:13 2009
Raid Level : raid5
Used Dev Size : 1454894336 (1387.50 GiB 1489.81 GB)
Array Size : 2909788672 (2774.99 GiB 2979.62 GB)
Raid Devices : 3
Total Devices : 4
Preferred Minor : 1
Update Time : Thu Oct 29 18:37:53 2015
State : clean
Active Devices : 1
Working Devices : 2
Failed Devices : 2
Spare Devices : 1
Checksum : ca5c1582 - correct
Events : 3329174
Layout : left-symmetric
Chunk Size : 256K
Number Major Minor RaidDevice State
this 0 8 66 0 active sync
0 0 8 66 0 active sync
1 1 0 0 1 faulty removed
2 2 0 0 2 faulty removed
3 3 8 50 3 spare /dev/sdd2
/dev/sdd2:
Magic : a92b4efc
Version : 0.90.00
UUID : cd57d356:c19317bf:a7df5645:f34ebdb2
Creation Time : Fri Mar 20 17:53:13 2009
Raid Level : raid5
Used Dev Size : 1454894336 (1387.50 GiB 1489.81 GB)
Array Size : 2909788672 (2774.99 GiB 2979.62 GB)
Raid Devices : 3
Total Devices : 4
Preferred Minor : 1
Update Time : Thu Oct 29 18:37:53 2015
State : clean
Active Devices : 1
Working Devices : 2
Failed Devices : 2
Spare Devices : 1
Checksum : ca5c1572 - correct
Events : 3329174
Layout : left-symmetric
Chunk Size : 256K
Number Major Minor RaidDevice State
this 3 8 50 3 spare /dev/sdd2
0 0 8 66 0 active sync
1 1 0 0 1 faulty removed
2 2 0 0 2 faulty removed
3 3 8 50 3 spare /dev/sdd2
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