RAID Mirroring on a Mac Pro

A couple weeks ago I walked into my office, turned on my monitor, and saw a gray screen. Odd, I thought. Rebooted. Same gray screen. Rebooted. Nothing but gray.

I have one of those new-fangled Intel Mac Pros, so I had to look up how to boot into a different mode. I fired up my PC and found the handy document: My Mac Won't Start!. As I went through all of the options I kept getting the dreaded gray screen. The contents of my hard drive flashed before my eyes. I thought for sure I'd lost my data, and I was starting to make a list of things I would need to reconstruct. After exhausting my options, I called Apple Support and they confirmed that my Mac would need professional help.

To make a long story short, my hard drive was fine. The internal power unit had failed, and two weeks later I got my Mac Pro back in working order with a new power unit. But the event gave me backup religion, and I decided to look into backup options so I wouldn't have to worry about loosing recent work and the thousands of files, emails, and media I've gathered over the years.

The Mac Pros have RAID software built in, so I decided to move from my default 250 gig drive to two mirrored 500 gig drives. RAID stands for redundant array of inexpensive disks and the idea behind mirroring (aka Raid 1) is that you have two or more disks with exactly the same data. If one disk fails, you can use one of the others until you get a replacement. Plus a drive failure won't mean lost data. I think of it as an insurance policy for my virtual stuff.

The process of setting up a RAID set was fairly simple, but I thought I'd step through the process here to share my experience. Here's what you'll need to move from a single drive to RAID mirroring on a Mac Pro:
  • Mac OS X (10.4+)
  • Two 500 gig drives
  • External hard drive case
I looked for quiet drives and eventually settled on Western Digital Caviar SE16 drives. I found them as OEM drives (plastic bag packaging only) at Newegg for $169.99 each. I didn't have a SATA external drive case, so I picked one up at my local Mac Store for about $75. (I picked up a Macally PHR-100SU.) You can probably find external cases cheaper by looking around a bit, though.

Once you have everything you need, you want to initialize your new drives, set up a RAID mirroring set, and copy your current drive to your new RAID set. It goes like this:
  1. Remove the current drive.
  2. Install the two 500 gig drives.
  3. Install the current drive into the external drive case.
  4. Plug in the external drive, boot.
The Mac Pro will boot from an external USB device. You just need to be patient. Eventually the Mac will automatically detect that your OS is now on an external drive. (You could probably also boot from the CD that came with your computer and skip the whole external case thing, but I went the case route.) Now that you've booted into your current drive, start up Disk Utility in the Applications/Utilities folder, and continue:
  1. Partition the new drives.
  2. Click the RAID tab, drag both new drives into the box, click Create.
  3. Click the Restore tab.
  4. Drag the current drive (external) icon to the Source field.
  5. Drag the new mirrored set icon to the Destination field.
  6. Click Restore.
Once this process starts you might want to go out for a coffee. And a movie. And maybe some shopping. You're copying your old disk to your new RAID set, and it'll take several hours (depending, of course, on how much data you have on your current disk).

Once the restore is complete, shut down. Unplug your external drive, and fire up your computer. Your Mac might sit on a gray screen while it looks for an OS to boot into, but you should soon find yourself back on your computer as if you'd never left.

So what did I get out of all this work and the $450 I spent? Well, I now have two hard drives storing my data. In my case, I also got double the hard drive space (I went from 250 gigs available to 500 gigs). I didn't get a performance boost by moving to RAID. With mirroring, the OS has to write everything to two drives now, and I haven't noticed any change. Sometimes I think I sense the system as slower, but it's probably my imagination. But any performance trade-off is so slight, it's worth having protected data. And to top it off, I still have my original 250 gig drive that I can leave in the external case. I might also install the drive internally, and use it for more non-mirrored storage.

The bottom line is that Apple has made RAID disk mirroring extremely easy to set up, and I can sleep a little easier at night knowing that if I wake up to a gray screen (or worse) it won't be the end of my data world.
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