Is Time Machine all you need?

Although any backup is better than no backup at all, Time Machine may not protect your data to the extent or in the way that you need. A few significant weaknesses offset its impressive strengths.

Time Machine copies the files on your computer to a destination you designate—an external hard drive, a second drive inside your Mac, an extra partition on your internal hard disk, a network server, or Apple’s new Time Capsule device. Then, once an hour, the program runs again, updating your backup to include whatever files have changed since last time.

With each hourly backup, Time Machine takes what amounts to a snapshot of your entire system at that moment. If you look through the folders on your backup disk, you’ll see what looks like a complete copy of all your files for each of numerous backup sessions. But to some extent that’s an illusion; Time Machine copies to your backup disk only those files and folders that are different from the ones in your previous backup. Using a bit of Unix magic known as hard links, Time Machine can store just one copy of a file or folder but make it appear to be in several places at once. That way, your disk doesn’t fill up with multiple copies of files that haven’t changed.