Cloning your disk to another connected to your Mac
Apps such as SuperDuper! and Carbon Copy Cloner let you mirror the contents of your internal disk to an external drive, and can set schedules so that this happens, say, daily at 3 a.m. so that it’s not getting in the way of your work.
If your internal disk fails, you can just boot from the external clone and continue as if nothing had changed. Obviously, you don’t want to rely on this solely, or be doing it for long; it might be slow, and it means you’re a level of redundancy down, so that if the external clone fails, you’re in big trouble. But you can’t beat it as a way to keep you running while you get the internal fixed.
Connect a cheap little hard disk, tuck it out of the way, and just let your Mac clone to it daily. In our example scenario in the picture above, the disk is connected to the USB hub in an Apple Cinema Display, and kept out of sight in a TwelveSouth HiRise; this slows it down to USB 2.0 speeds, but that doesn’t really matter, in part because the clone happens at night, but also because after the initial backup, SuperDuper can update only those files that have changed.
If you have a PowerPC Mac and want to be able to boot from your clone, the disk you use for this has to connect using FireWire rather than USB (since PowerPC Macs can’t boot from USB).
Technically, you can also clone to a disk image on a network drive rather than to a local disk, but while this has merit in edge cases, it’s not usually the best option.
Good because: Creates perfect copy of your internal disk, which you can restore from, or, best of all, boot from in an emergency.
But be aware that: There’s no versioning, it can be slow depending on the interface, and there’s no protection against local disasters.