Revisiting the OptiBay with Time Machine

Back in June, I covered MCE's OptiBay Hard Drive, a unique upgrade for MacBooks and MacBook Pros that replaces the laptop's optical drive with a second internal hard drive. (You use an external optical drive when necessary.) As I noted back then, the upgrade isn't for everyone, but it's a great solution for people who need to maximize their on-the-go hard-drive space, want a completely separate drive for Windows (via Boot Camp), or want the security of always having a bootable backup right there inside their laptop.

Before Leopard, I took advantage of the last approach: If you use a utility such as SuperDuper or Carbon Copy Cloner to maintain an up-to-date clone of your primary drive on the OptiBay drive, you've always got a bootable emergency disk that's a mirror-image copy of your main drive (at least at the time of the last clone update). This internal clone isn't an ideal backup from a data-safety standpoint--if someone steals your laptop, they get the backup, as well, so you should also keep another backup separate from your laptop. However, if you ever experience a hard-drive disaster, you can just boot from the OptiBay drive and be back up and running in a matter of minutes.

But now that Leopard is out, our tweaked MacBook Pro has become my Leopard-testing machine, and I've discovered another use for the OptiBay drive: hosting Time Machine backups. As with any internal or external hard drive, you simply assign the OptiBay drive to Time Machine, and you've now got your Time Machine backups with you, and updated, at all times; if you ever accidentally delete data, or if a file gets corrupted, you can instantly recover it.

However, there are three caveats here. The first is that, as I mentioned above when talking about an internal clone, you'll also want another backup back home just in case something ever happens to your laptop as a whole. The second relates to battery life. By default, Time Machine backs up every hour; anything that's changed gets copied to the Time Machine drive. On a laptop running off battery power, this can reduce battery life. To conserve your battery, you've got a few options. You can use Disk Utility to unmount the OptiBay drive when using the laptop off battery power, and then mount it again when using AC power. You can turn off Time Machine (in the Time Machine pane of System Preferences) when you're on the go, and then turn it back on when you want to back up. (When Time Machine is disabled, you can still manually start a backup by clicking and holding--or Control/right-clicking--on the Time Machine icon in the Dock, and then choosing Back Up Now from the resulting menu.) Finally, you can change the length of the interval at which Time Machine automatically backs up using this procedure from Mac OS X Hints; by default, Time Machine backs up every hour.

The final issue is that, unlike a SuperDuper clone, a Time Machine backup isn't bootable. If your main drive ever has a problem that requires you to restore it from your Time Machine backup, you must boot from the Leopard Install disc to do so. Not only is this slow, but in the case of an OptiBay-equipped laptop, you may find yourself out and about without an optical drive.

My solution to this dilemma was to divide the OptiBay drive into two partitions: one 10GB in size, and the other comprising the rest of the disk. I then used Disk Utility to clone my Leopard Install disc to the 10GB partition and told Time Machine to use the other partition for backups. If disaster ever strikes, I can just boot off the Install partition and, once the Installer runs, choose Restore System From Backup from the Utilities menu. (This setup has the added advantage, compared to a standard Time Machine setup, that the "Mac OS X Install" partition is much faster to boot than the actual OS X Install DVD.)

Of course, the clone approach still offers the quickest way to get back up and running after a drive failure or other catastrophe. However, this Time Machine arrangement has a few advantages of its own. For one, backups occur more frequently, by default. For another, Time Machine provides versioned backups--I can recover the version of a particular file from earlier today, two days ago, or last week. Finally, I get Time Machine's ease of setup and file recovery. I haven't decided which approach I'll stick with in the long run, but I'm enjoying having so many options.

(If you don't want to go the OptiBay route, much of the above discussion also applies to an external hard drive.)