If you've installed any antivirus software on your Mac, you'd do well to exclude your backup disk from virus scanning, as this can slow down Time Machine – the files have, after all, already been scanned.
Check the Help section of your chosen antivirus product for details on setting exclusion policies.
If you're using Aperture, Apple's image management and processing software, Apple advises that you should have at least Mac OS X 10.5.3 if you intend to use Time Machine to back up your Aperture Library. The only reason given by Apple for this is that "earlier versions of Leopard did not provide full compatibility between Time Machine and Aperture".
Using certain characters in your Mac's name in the Sharing System Preferences pane can cause some backups not to appear when you attempt to restore a file using the Time Machine interface. You should therefore go to System Preferences > Sharing and make sure that the Computer Name field contains only numbers and upper or lowercase letters.
Backing up multiple Macs
You can use a single disk to back up multiple Macs, as Time Machine will create a different backup folder for each. If you're moving the same disk between a number of Macs or sharing a Time Capsule, you should make sure that each Mac is given a different name in System Preferences > Sharing, using the guidelines above.
You can, incidentally, make backups across an Ethernet or AirPort network using a FireWire or USB 2.0 drive attached to one of your Macs: just remember to enable Personal File Sharing in System Preferences > Sharing. This is probably not the most efficient way of backing up, as network traffic is greatly increased during backups.
If you dismissed the Time Machine dialogue the first time you attached your external disk, no problem. Once you're ready to start backing up, go to Time Machine's System Preferences pane, where you can choose your backup disk and get started. We'll show you how in our step-by-step guide later on.
You don't have to back up every single item on your Mac's hard disk: for instance, you might want to exclude all system files. This makes sense if you want to conserve space on your backup disk; you can always use either the installation discs that came with your Mac or a bought copy of Leopard to install a clean copy of your system after a system crash. You won't, however, have the option of using your Time Machine backup to perform a full system restore should the need arise.
Creating your first backup
When Time Machine creates its first backup, it takes quite a while to do it. This is because it's making a complete copy of everything you've chosen to back up. After this initial backup, Time Machine will make copies only of those files that have been changed since the previous backup – a so-called 'incremental' backup.
Time Machine makes backups every hour, as long as your backup disk is attached to your Mac and your Mac is turned on and active (that is to say, not in Sleep mode). In fact, it takes backups every hour out of the previous 24 hours, daily backups to cover the past month and then every week until your backup disk is full. Unless you're happy to overwrite your oldest backups, you'll need to attach another disk once your current one is full and choose it in System Preferences > Time Machine – just make sure it has a different name to the previous one. If Time Machine is unable to take a backup it will resume its duties the next time your Mac is awake and the disk is again available.
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