External Hard Drive and Time Machine

Hello scottb73,

Thanks for using Apple Support Communities!

We understand you are looking for some information about using Time Machine on an external drive for your Mac. We would be happy to look in to this with you and provide some guidance.

You can use an external drive for both Time Machine backups as well as storage for the Mac. You can see more information on what drives can be used and the steps to set up the drive for use with Time Machine here:

Back up your Mac with Time Machine

Backup disks you can use with Time Machine

If you wish to use the drive for storage as well as Time Machine backups, we would recommend creating a separate partition or new APFS volume for it. You can see how to create partitions or new volumes in these helpful articles:

Partition a physical disk in Disk Utility on Mac

Add, delete, or erase APFS volumes in Disk Utility on Mac

You can also use a single drive to store Time Machine backups from different Macs. When restoring a Time Machine backup file, you would be prompted for which backup file you want to restore to:

Restore your Mac from a backup

We hope this helps!

Kind Regards.

Yes, you can. I'd recommend partitioning the disk even for separate computers with Time Machine. It's not required, but that's the way to control the amount of space each machine takes. You typically want a TM backup drive to be 2-3 times the size of your internal storage data (which is not necessarily the size of your internal drive - you really shouldn't let your internal drive get >80% full, ever). If you have two Macs backing up to the same volume, one Mac may 'take over' the bulk of the backup space (for example, if you have large video files then delete them from the internal drive, that sort of thing makes the backup grow faster).

As an example, I have a LaCie rugged with 4 partitions (not APFS volumes, actual partitions), with one each dedicated to backup of a single Mac in the house, and the fourth partition used for general file backups.

As a side note, if you're willing to buy two drives you might consider keeping a second backup somewhere other than your house. It really depends on how much you value your data. Consider that a house fire may wipe out your Mac and your backup drive if that's stored at home. The LaCie Rugged I refer to above is the one I leave in my desk at work, and bring it home monthly to update the backups. At home I have a NAS system with TM backups for all the Macs in the house.