Inside Leopard's Time Machine: Backups for the rest of us
Think backups are a bore? Think again
Computerworld - Since Apple Inc. first announced the initial 10 features of Mac OS X 10.5 "Leopard" in August 2006, the one that has captured the most interest of Macintosh fans is Time Machine. Apple has billed Time Machine as the backup tool for people who hate the task. That's almost everyone, according to Steve Jobs, who says only 4% of computer users regularly back up their data.
So simple, there's no Step 3
One of Apple's early iMac commercials described connecting to the Internet as being so easy that "there's no Step 3." As I was trying to sum up how easy Time Machine is to configure, that commercial popped into my head.
In fact, Step 1 -- plugging in an external hard drive after installing Leopard -- is the only step that's truly required. Leopard will automatically detect the hard drive and ask whether you want to use it for Time Machine backups. If you say yes, that's really all you need to do.
Time Machine's easy setup. (Click for larger view.)
Time Machine will then perform an initial backup to the drive, which can take quite some time -- a couple of hours or more for most people, depending on the contents of your internal hard drive. You may actually want to start your initial Time Machine backup before going to bed and let it run overnight.
Once the initial backup is performed, Time Machine will back up new and changed files every hour (in technical backup-speak, it is performing an hourly incremental backup) while the backup drive is connected.
If the backup drive is not available, as is often the case with a portable Mac, Time Machine will resume its backups as soon as the drive becomes available.
At midnight, or as soon thereafter as your computer is on and the backup drive available, the most recent hourly backup will be saved as a daily backup, and earlier hourly backups will be deleted to save space. Each daily backup is maintained for a month. After a month, Time Machine converts one of those daily backups into a weekly backup that it preserves indefinitely (or until your backup drive becomes full).
When a drive becomes nearly full, Time Machine analyzes its backups and deletes files in a method designed to preserve as wide a range of backup dates as possible while still allowing you to have a fully restorable backup of your current system. If you are concerned about losing any potential backup files, you can configure Time Machine to warn you when it runs low on disk space.
Time Machine's approach of keeping frequent recent backups and fewer older backups may seem unorthodox, but it really is brilliant when you think of Time Machine as a safety net. If you want to revert to an earlier version of a file you're working on or if you accidentally delete something, you usually know it very quickly. Having hourly backups means you can go back through your version choices easily -- it functions almost like a universal-undo feature. It also means that if you have a hard drive failure, you will have an extremely recent backup to restore from, and there will be almost no data loss.
The balance to this is disk space and the ability to find files. Sorting through hourly backups from six months ago would be like looking for a needle in a haystack, and storing all those backups could theoretically require several terabytes of disk space. Having a day's worth of hourly backups, however, offers an incredible value and makes Time Machine more useful in the daily use of your Mac. It really is revolutionary to add this capability on top of the typical once-daily (or less-frequent) approach of other backup tools.
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