Dear List,
I use MD RAID 5 since some years and so far had to recover from single
disk failures a few times which was always successful.
Now though, I am puzzled.
Setup:
Some PC with 3x WD 1 TB SATA disk drives set up as RAID 5 using kernel
2.6.27.21 (now); the array ran fine for at least 6 months now.
I check the state of the RAID every few days with looking at
/proc/mdstat manually.
Apparently one drive had been kicked out of the array 4 days ago without
me noticing it.
Root cause seemed to be bad cabling but is not confirmed yet.
Anyway, the disc in question ("sde") reports 23 UDMA_CRC errors,
compared to 0 about 2 weeks ago.
Reading the complete device just now via DD still reports those 23
errors but no new ones.
Well, RAID 5 should survive a single disc failure (again) but after a
reboot (due to non-RAID related reasons) the RAID came up as "md0 stopped".
cat /proc/mdstat
Personalities :
md0 : inactive sdc1[1](S) sdd1[2](S) sde1[0](S)
2930279424 blocks
unused devices: <none>
What's that?
First, documentation on the web is rather outdated and/or incomplete.
Second, my guess that "(S)" represents a spare is backuped up by the
kernel source.
mdadm --examine [devices] gives consistent reports about the RAID 5
structure as:
Magic : a92b4efc
Version : 0.90.00
UUID : ec4fdb7b:e57733c0:4dc42c07:36d99219
Creation Time : Wed Dec 24 11:40:29 2008
Raid Level : raid5
Used Dev Size : 976759808 (931.51 GiB 1000.20 GB)
Array Size : 1953519616 (1863.02 GiB 2000.40 GB)
Raid Devices : 3
Total Devices : 3
Preferred Minor : 0
...
Layout : left-symmetric
Chunk Size : 256K
The state though differs:
sdc1:
Update Time : Tue Apr 7 20:51:33 2009
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Checksum : ccff6a15 - correct
Events : 177920
...
Number Major Minor RaidDevice State
this 1 8 33 1 active sync /dev/sdc1
0 0 0 0 0 removed
1 1 8 33 1 active sync /dev/sdc1
2 2 8 49 2 active sync /dev/sdd1
sdd1:
Update Time : Tue Apr 7 20:51:33 2009
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Checksum : ccff6a27 - correct
Events : 177920
Layout : left-symmetric
Chunk Size : 256K
Number Major Minor RaidDevice State
this 2 8 49 2 active sync /dev/sdd1
0 0 0 0 0 removed
1 1 8 33 1 active sync /dev/sdc1
2 2 8 49 2 active sync /dev/sdd1
sde1:
Update Time : Fri Apr 3 15:00:31 2009
State : active
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Checksum : ccf463ec - correct
Events : 7
Layout : left-symmetric
Chunk Size : 256K
Number Major Minor RaidDevice State
this 0 8 65 0 active sync /dev/sde1
0 0 8 65 0 active sync /dev/sde1
1 1 8 33 1 active sync /dev/sdc1
2 2 8 49 2 active sync /dev/sdd1
sde is the device that failed once and was kicked out of the array.
The update time reflects that if I interprete that right.
But how can sde1 status claim 3 active and working devices? IMO that's
way off.
Now, my assumption:
I think I should be able to either remove sde temporarily and just
restart the degraded array from sdc1/sdd1.
correct?
My backup is a few days old and I would really like to keep the work on
the RAID done in the meantime.
If the answer is just 2 or 3 mdadm command lines, I am yours :-)
Best regards
Frank Baumgart
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