南台灣小白鯨

Time Machine lets you automatically back up your entire system in Mac OS X.

"Setting up Time Machine is as easy as connecting an external hard drive to your Mac via FireWire or USB, or by connecting to a Time Capsule. You can also use a secondary internal disk if your desktop Mac has one (that is, a disk that you don't start up from). " -- http://support.apple.com/kb/HT1427

If you want to use NAS to be your Backup Disk,  use the command below:

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1