Information Technology Reference
3. In the dialog that appears ( Figure 12 ), enter and verify a password
for your Time Machine backups and click Encrypt Disk.
Figure 12: Enter and verify a password, and click Encrypt Disk.
Encryption may take some time (progress is shown in the Time
Machine menu), but you can continue to back up and restore data
with Time Machine while it's happening.
Note: Keep in mind that this encryption affects the entire volume
(disk or partition) containing your Time Machine backups.
Use a Single Backup Disk with Multiple Macs
You can use Time Machine to back up more than one Mac to a given
drive (with or without a Time Capsule). A single partition can store
backups for any number of Macs, without getting them confused, as
long as it has enough free space. In most cases, you don't have to do,
or know, anything special; just plug in the drive (or connect to it over
your network), select it in the Time Machine preference pane, and let
the backup run; repeat the procedure with each computer you want to
back up. If you're physically moving the drive between machines, Time
Machine should automatically recognize it and back up on its regular
schedule, without further intervention, after the first backup.