Backing up at multiple locations
How to use Time Machine at work and home
If you haven’t already set up your first backup disk for use with Time Machine, connect the disk to your Mac; Time Machine will ask whether to use it as a backup disk. If there are files on the drive that you need to keep, copy them elsewhere before responding to the prompt. When you’re ready, decide whether to encrypt the disk’s contents, then click “Use as Backup Disk” – you may also be asked whether to reformat it.
Don’t carry your backup disk around with you, even if it’s a portable disk. For convenience, Time Machine is engineered to work with multiple disks, so you can back up at several locations. Connect a second backup disk to your Mac, go to Time Machine’s preferences, click the option to select a disk, then choose your secondary backup target from the list that is presented. When asked whether to replace or complement the existing disk, choose Use Both.
When you reconnect a backup disk, Time Machine backs up all changes to your Mac since that particular disk was last used, not just those since the last backup.