About a year ago I thought it would be a good idea to buy a spare hard drive and set up RAID 1 (mirrored) on my computer. I've gotten so many emails from users of Senuti who have had failed hard drives. It kind of made me paranoid that my hard drive would fail. A second internal hard drive wasn't too expensive, so I went ahead and bought one.
I got pretty much the same model as the one that came with the computer. Same size and everything; it might have just been a generation newer, but for all intensive purposes, the same drive. It took me a while to get around to setting up the RAID because I needed to format the drive at the same time. I did get around to it eventually, and it went pretty well. Disk Utility was pretty easy to use to set it up. I got a partition on each of the two disks to mirror each other.
Fast forward a year when I decided to try to get more than one partition to work with RAID 1. I don't claim to be an expert with RAIDs, but I can't think of any reason that you wouldn't be able to set up two disks with multiple partitions to mirror each other. Partitions A1, B1, and C1 on the first drive could mirror partitions A2, B2, and C2 on the second drive if the sizes were the same. Disk Utility doesn't let you do this. It doesn't tell you that you can't, though. It will just go ahead and attempt it anyway. You can set up A1 to mirror A2 just fine, but if you try to make B1 mirror B2 it will probably fail to work and also put your A1-A2 RIAD into a degraded state. When I did this, A1 and A2 held all of my important data.
So at that point my startup disk was a degraded RAID, and things didn't work so well. My computer started up sometimes. I managed to save all of my data (a long, scary process) and decided to go with a RAID 1 on one partition which had worked before. This worked fine for about a month, but then my computer started to freeze and stop responding entirely. Restarting led to it just logging me off -- normally within the first 2 minutes -- and showing me a blue screen. So I reinstalled OS X on a separate (non RAID) partition and the computer started just fine. But the RAID unmounted itself unexpectedly after 2 minutes of the computer being on. That explained why it just logged me off before. I was able to recover my data again, and left the RAID partition in its unstable state for a while thinking it wasn't really affecting anything.
Last night I realized it was affecting things. I tried playing a DVD, and the DVD wouldn't play. I thought it was just that the computer couldn't read the disk. It turns out that my computer wouldn't mount anything that wasn't available when the computer was booted.
I removed the RAID partition, and everything appears to be working normally now. RAID 1 doesn't seem like it would be all that difficult for Apple to get working. I realize it's not something most Mac OS X users would use, but its a very valuable tool for some. For now I'm going to have to resort to drag and drop backup to the second drive. Apple's Time Machine should make backup to the drive easier, but RAID 1 makes it automatic. Too bad.
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