One of the drives in my RAID-5 array is showing uncorrectable errors:
Nov 28 17:52:36 beast smartd[8184]: Device: /dev/sdc, 1 Currently
unreadable (pending) sectors
Nov 28 17:52:36 beast smartd[8184]: Device: /dev/sdc, 1 Offline
uncorrectable sectors
And it fails a self-test:
SMART Self-test log structure revision number 0
Warning: ATA Specification requires self-test log structure revision
number = 1
Num Test_Description Status Remaining
LifeTime(hours) LBA_of_first_error
# 1 Short offline Completed: read failure 20% 931
1953520763
Now that's not good but it's probably not bad enough to get the drive
replaced. (Opinions?) Anyway, rewriting the sector ought to "cure" it,
so how do I do that?
Here's the details of my array:
[root@beast md]# mdadm --detail /dev/md1
/dev/md1:
Version : 00.90.03
Creation Time : Mon Jul 28 15:49:09 2008
Raid Level : raid5
Array Size : 1953310720 (1862.82 GiB 2000.19 GB)
Used Dev Size : 976655360 (931.41 GiB 1000.10 GB)
Raid Devices : 3
Total Devices : 3
Preferred Minor : 1
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Fri Nov 28 17:56:22 2008
State : active
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 256K
UUID : d8c57a89:166ee722:23adec48:1574b5fc
Events : 0.6112
Number Major Minor RaidDevice State
0 8 2 0 active sync /dev/sda2
1 8 18 1 active sync /dev/sdb2
2 8 34 2 active sync /dev/sdc2
I tried:
[root@beast md]# mdadm /dev/md1 --fail /dev/sdc2
mdadm: set /dev/sdc2 faulty in /dev/md1
[root@beast md]# mdadm /dev/md1 --remove /dev/sdc2
mdadm: hot removed /dev/sdc2
[root@beast md]# mdadm /dev/md1 --add /dev/sdc2
mdadm: re-added /dev/sdc2
but that finished instantly. I guess it would since the array has a
write-intent bitmap and it's noticed that sdc2 is being re-added. I
could tell the system to do a complete resync with:
# echo repair > /sys/block/md1/md/sync_action
but really I want to tell the system to rebuild entirely from sda2 and
sdb2, onto sdc2. At least I think I do. I've a feeling the answer is to
zero the superblock, but I'm not confident about doing that because I'm
not sure if re-adding the thing without a superblock will either work or
do the Right Thing[tm].
Cheers,
John.
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