Easy Redundant Mac Backups with Time Machine and Multiple Drives

Having reliable and regular backups of your Mac should be considered a mandatory part of maintenance, and for most users Time Machine provides that with easy and peace of mind. But what if you want multiple backups stored in different places, like a backup at home, and another at the office, or perhaps a backup at home and a portable backup drive for the road? Or what if you just want to have a backup of your backup drive for data redundancy?

Time Machine can address any of these situations by allowing you to set a secondary backup drive, which provides an additional duplicate backup to another hard drive. Setting this is up is quite simple.

How to Use Multiple Hard Drives for Time Machine Backup Redundancy in Mac OS X

This feature is available in all versions of OS X with Time Machine support:

1. Connect the additional drive to use for as a redundant backup to the Mac – if the drive is brand new you may need to format it first for OS X compatibility using Disk Utility
2. Open Time Machine preferences, found within System Preferences via the  Apple menu
3. Click “Select Disk”
4. Ignoring the already chosen “Backup Disks” section, look under “Available Disks” and choose the additional secondary backup drive to use, then choose “Use Disk” *



5. Time Machine will now ask if you want to replace the existing backup disk or use both disks, choose “Use Both”

* Optionally, you can set encryption for the backup(s) if you use it

The secondary drive will now be set as an additional Time Machine backup. Because the secondary backup is starting from scratch, it can take a while to complete the first backup to it, so you will probably want to leave it connected for a while as Time Machine does its job.

All future backups will be completed sequentially in turns, finishing on the first drive before moving on to backup to the secondary drive. That means your backups will take twice as long if both drives are connected at the same time, though that generally has little impact on system performance for most tasks unless you’re really aiming to optimize performance on a Mac for resource intensive uses where speed matters. If both drives are not connected simultaneously (which may be the case for having backups in multiple locations, i.e. the office and home), then Time Machine will backup to either drive that is available whenever it is connected to the Mac. That either-or-both methodology applies to both the automated backups and also to manually initiated backups.

If you do have both drives connected to the Mac at the same time and you wish to browse the secondary drive through Time Machine, just hold down the OPTION key and click the Time Machine menu bar item, choosing “Browse Other Backup Disks”.

All in all, this provides an excellent solution for data redundancy, and for users who want extra reassurance that their backups will be there for them regardless of the health of a hard drive or their location, using two Time Machine drives is often the simplest solution.