Using Time Machine to backup and restore external disks


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.