Information Technology Reference
The downside is that you have to do a lot of unplugging, moving, and
replugging to move the drive between computers. And, backups can
occur for a given computer only while the drive is connected.
Network backups—whether to a Time Capsule, a NAS, or a drive
attached to another Mac with File Sharing turned on—are great for
multiple Macs because you almost never have to intervene. Just leave
everything connected, and all the computers on your network back up
automatically. In fact, you can even back up wirelessly using a Wi-Fi
The main problem is speed; not only will backups take much longer
over a network than with a locally attached drive, they'll also slow
down other things you may be doing on the network. On the other
hand, while the initial backup of each computer over the network will
take some time, subsequent updates should go much more quickly.
When considering a network backup, keep these facts in mind:
Time Machine can see a network volume only if it's attached to a
Mac, a Time Capsule, or one of the few NAS devices that's expressly
designed to work with Time Machine.
In order to make an external drive available to other computers on
your network, you must share it. See the sidebar Share a Volume
(just ahead) for instructions.
The computer to which the external drive is connected must be
turned on and awake in order for other computers to use it. (Read
the sidebar Power Management and Backups for advice on how to
wake a sleeping Mac for a backup.)
Wired networks usually provide considerably faster performance
than wireless networks. As wired networks go, bigger numbers are
better—Gigabit Ethernet (1000 Mbps) is faster than Fast Ethernet
(100 Mbps), which is faster than conventional (10 Mbps) Ethernet.