10.4: How to enable booting from multiple clones

Nov 02, '07 07:30:09AM

Contributed by: Roph

I'm a big fan of using SuperDuper (or CarbonCopyCloner or even Disk Utility) to make bootable clones of my startup volume as an important part of my backup strategy. In fact I like to not only keep a most recent clone, but several historical ones as well.

So I was delighted when I recently discovered I could buy 500GB and 750GB external FireWire hard drives for under $200, and assumed I could simply format them into multiple boot-volume-sized partitions into which I could place clones, as I had so often and easily in the past. However, I eventually became dismayed when I later discovered that while I could use SuperDuper and other programs to create multiple clones, the only clone that I could actually boot would be the first bootable clone in partition order encountered on the drive.

With a hint from an Apple Genius, I eventually discovered the source of my difficulty. Whereas at some point in the past Disk Utility would use Apple Partition Map as the default partition format, appropriate for booting volumes on a PPC Mac, that is no longer the case in Tiger. Instead I discovered that Disk Utility was using the Master Boot Record format appropriate for Windows; probably because it discovered that, as shipped, the new drives were already pre-formatted with this Windows-centric partition format.

It is quite simple to determine what partition table format has been used on your internal or external hard drives. Simply run Disk Utility, select the drive of interest (not one of its individual partitions), select the Partition tab, and look at the last line displayed at the bottom of the window after Partition Scheme:. You should discover one of three alternatives:

As long as you don't have a compelling need to boot from a clone saved to a partition, the format may not matter. It has also been rumored that this restriction may be relaxed in 10.5, though I haven't tested that. But with Tiger 10.4.10 at least, if you want the ability to boot from a choice of multiple clones stored in various partitions of a drive you should explicitly set the desired Partition Table format at the time you partition the drive.

This too is quite simple. In the Partition tab of Disk Utility, where you set the number and size of the partitions, make sure you click on the Options button to select the desired partition format prior to pressing the Partition button that performs the work.

Backup early, backup often, and partition well.

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