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Move your Time Machine backup and continue using it to backup

This advanced tip allows a Time Machine backup to be made and transferred to an alternative storage location, all while still being available as a backup disk.

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Joe Aimonetti
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This advanced tip allows a Time Machine backup to be made and transferred to an alternative storage location, all while still being available as a backup disk. Using Terminal, users can move their backup disk without losing the previous history stored in the backup.

This process involves using Terminal to make a copy of your Time Machine disk and subsequently transfer it to a new location while still allowing it to be accessible for continued backups (via macosxhints.com user "zegor"):

  1. Create an image (optionally encrypted) of the same size as the Time Machine hard disk. You can use the script from this hint, or simply copy and execute the relevant parts of it. With the script, the command would look something like this:
    mkBackupImage.sh -p /path/to/disk/image -s nnn
    **Replace the nnn with the size of the original Time Machine disk (and replace the path bit, too).
  2. Mount the new image:
    open /path/to/disk/image
  3. Use asr to make a block copy of the hard disk to the image:
    sudo asr --source /Volumes/TM_backup --target /Volumes/mounted_image_name --erase
Caution: Make sure your 'asr' copy is done by block copy (not file copy). See 'man asr' for help with this.

Testing: I have tried this in a minor way. I created a Time Machine backup, backed up to it a few times, followed the above hint, and then shifted Time Machine to back up to the NewTimeMachine disk. Time Machine will mount the disk image, and back up to it.

Bugs: When restoring from the image, one has to (1) mount the image (open the image file in the Finder), (2) Control-click the Time Machine icon in the dock, and (3) pick 'Browse other time machine disks...' from the contextual menu.

I have not tested this solution personally, though comments on the original post by "zegor" concerning copyable Time Machine backups relay pretty good success with the process. As always, when working in Terminal be sure to have a secure and stable backup of all your important data should something go wrong.

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