Ivorde Unix/Linux/Database/Web/Mail Forum

I'm not going to explain what a software RAID is. There is google for this.
However, i will try to summarize here how to remove a failed disk and add a new one instead of it. Follow the steps and ask if somethig failes...

1. Set the drive (in my example /dev/sda) as faulty


2. Remove the faulty disk from the array


3. Stop the array


4. Re-assemble the RAID device


You should have something like this now (sizes and name may be different)


5. Add the new good disk to the raid array


You should have it like this now:

I have a software raid 1 with mdadm and two 1 TB disks. Today I booted and I saw the the message that the raid activated normal but with only one out of two disks. So I I got the following output form this command:
mdadm -D /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Sat Apr 16 00:30:53 2011
Raid Level : raid1
Array Size : 976758841 (931.51 GiB 1000.20 GB)
Used Dev Size : 976758841 (931.51 GiB 1000.20 GB)
Raid Devices : 2
Total Devices : 1
Persistence : Superblock is persistent

Update Time : Tue Oct 18 18:33:39 2011
State : clean, degraded
Active Devices : 1
Working Devices : 1
Failed Devices : 0
Spare Devices : 0

Name : archiso:0
UUID : 96ad7277:0da83ae5:25ef36da:cb4596d3
Events : 880419

Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 0 0 1 removed
So I tried to re-add the disk with this command:
sudo mdadm --re-add /dev/sdc1 /dev/md0
but I got this error:
mdadm: /dev/sdc1 does not appear to be an md device
In gparted I also can see the disk and in the BIOS, too, so it's there and the disk seems to work.
Can anyone tell me what to do and I don't want to loose data and too much time and just re-add the disk. (Of course I do have backups!!)

Try: