As part of a good backup strategy, you should always have more than one version of your data. Even though you may backup all of your data to a Time Machine disk, disks do fail and you could risk losing all of your data.
A good practice then, is to back up your data to multiple Time Machine disks. With Mountain Lion, you can use a rotation of several disks, ensuring that if one disk fails you won’t lose everything.
To Set Up Multiple Backup Disks in Time Machine
- Click from the menu and click System Preferences.
- Click Time Machine under the System category.
- Click the Select Disk button.
- Click the disk you want to use under the Available Disks area of the window.
- When asked if you wish to use both disks or replace Time Machine, click Use Both.
You will now be able to rotate Time Machine disks.