I have a customer that had a RAID array setup by a previous tech. They have 2 80Gb 7200RPM IDE disks in a RAID 1 config. Well they are getting a message stating that one of the drives is unallocated.
Now, Im pretty new to RAID and have never setup a RAID 1 array. So what I would like to know is:
1) Is this message popping up because one of the drives has failed?
2) If one of the drives did fail, can I just install a new drive and have RAID recreate the back up on the new disk?
3) If yes on #2, how do I make a backup on the new disk?
4) If one of the disks is bad, how do I make sure which drive is bad? I obviously dont want to remove the good drive and leave the bad one in the machine.
5) If this message is NOT because of a bad disk, how do I reallocate the drive?
6) To reallocate the drive, do I have to reformat?
1) more likely the RAID failed - metadata that is not recognised or some other internal error; it may also be the response of the RAID engine to purposely "unallocate" a drive after it did not respond in time to some command. So it depends on what RAID engine you use; generally you would see this on Windows-based fakeRAID systems.
2) Yes, you should be able to rebuild the array by adding a new drive. The danger is that the RAID engine should not rebuild the existing drive with the data of the new drive; but should rebuild the new drive to mirror the data on the already existing drive. Make sure you follow the right steps for your specific RAID engine.
3) RAID is no backup; its called a mirror. Once you add the new drive to the existing RAID volume, it should trigger a rebuild of the new drive. So this mirroring happens automatically, when the RAID drivers are active.
4) Check the SMART values for any clues, particularly "pending sectors" and "reallocated sector" also "udma error count" should be zero while "ecc error count" is normal to be a very high number.
5) A full zero-write on the "failed" drive would clear any meta-data so it would be a brand new disk. Then add the disk to the existing RAID as already discussed.
6) A format under Windows XP is just a read-only operation. A format under Windows 7 is a zero-write operation and that's what you need. So a format under XP wouldn't work to clear the metadata located on the last sector on each drive. A zero-write using Ubuntu livecd would work also.
Please make sure your client understands RAID is no backup and can never replace one. And if the choice is between using RAID1 with no backup and two separate drives where one is a backup - then the backup solution is superior as it protects against more dangers and isn't vulnerable to any failures on the RAID level, such as which happened to your client.