Using Time Machine to backup and restore external disks

2021-8-24

Time Machine’s ability to backup external drives is quite handy. Recently, the file system on one of my external drives had gone bad and had to be formatted. That’s when I found out that you can use

tmutil restore [-v] src ... dst

to restore a disk from Machine and then use

tmutil associatedisk [-a] mount_point volume_backup_directory

to associate the newly-formatted drive with its existing backup. This way, you can keep your backup history and Time Machine does not need to perform a full backup on the new drive. Really handy.

It’s a good idea to turn off automatic backups while restoring the disk.