Hi,
I run a RAID5 array built from six 250GB Maxtor Maxline II SATA disks. After having several problems with Maxtor disks I decided to use a spare disk, i.e. 5+1 spare.
Well, *another* disk failed last week. The spare disk was brought into play seamlessly:
Thanks to some advice from Guy the "failed" disk is now back up and running.
To fix it I did the following;
Removed the bad partition from the array:
mdadm --manage /dev/md5 --remove /dev/sdd2
Wrote to the whole disk, causing bad blocks to be re-located:
[root@dude test]# dd if=/dev/zero of=/dev/sdd2 bs=64k dd: writing `/dev/sdd2': No space left on device 3806903+0 records in 3806902+0 records out
Verified the disk:
[root@dude test]# dd if=/dev/sdd2 of=/dev/null bs=64k 3806902+1 records in 3806902+1 records out
Added the partition back to the array:
[root@dude test]# mdadm /dev/md5 --add /dev/sdd2 mdadm: hot added /dev/sdd2
Quick look at the arrya configuration to make sure:
[root@dude test]# mdadm --detail /dev/md5
/dev/md5:
Version : 00.90.01
Creation Time : Thu Jul 29 21:41:38 2004
Raid Level : raid5
Array Size : 974566400 (929.42 GiB 997.96 GB)
Device Size : 243641600 (232.35 GiB 249.49 GB)
Raid Devices : 5
Total Devices : 6
Preferred Minor : 5
Persistence : Superblock is persistent Update Time : Wed Mar 2 02:01:24 2005
State : clean
Active Devices : 5
Working Devices : 6
Failed Devices : 0
Spare Devices : 1 Layout : left-symmetric
Chunk Size : 128K UUID : a4bbcd09:5e178c5b:3bf8bd45:8c31d2a1
Events : 0.7036368 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
3 8 82 3 active sync /dev/sdf2
4 8 66 4 active sync /dev/sde25 8 50 - spare /dev/sdd2
This raises the question: why can't md do this automatically? Not for the whole disk/partition, but just for a bad block when encountered? I envisage something like:
md attempts read one disk/partition fails with a bad block md re-calculates correct data from other disks md writes correct data to "bad" disk - disk will re-locate the bad block
Of course, if you encounter further bad blocks when reading from the other disks then you're screwed and it's time to get the backup tapes out!
Is there any sound reason why this is not feasible? Is it just that someone needs to write the code to implement it?
R. -- http://robinbowes.com
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