I am having trouble getting Time Machine to recognize my backup external HD, which is mounted and has been used successfully (yesterday) before.

Background: I just partitioned my drive to do a Boot Camp installation. Time machine was preventing me from having the space needed to do this, so I was forced to remove my backup drive and thin local snapshots by running 'sudo tmutil thinlocalsnapshots / 999999999999' as described here. Of course, I backed up right before doing all this. This worked and I successfully finished the Windows install, but now when I go back to Time Machine and try to have it resume backing up, the volume it was using does not appear as an option under 'select backup disk.'

Curiously, when I option-click the Time Machine icon and choose 'Browse other backup disks,' it recognizes the previous backups just fine and will let me go into Time Machine and browse through them. But it won't let me choose this disk to resume backing up. So it would seem that all I need to do is re-establish this backup as linked with the computer, without reverting to it, but I can't find any way to do this.

I don't have enough storage to copy my external HD anywhere else, and I am hoping to avoid losing my previous backups. Any ideas?

  • The simplest may be to buy a new harddisk to use with a fresh Time Machine and store the one you have permanently offsite as a precaution against fire, meteor strikes, burglary or anything else that would affect all electronics in your home. – Thorbjørn Ravn Andersen Jun 2 at 17:58
  • Simplest, perhaps, but not ideal! – Rococo Jun 3 at 23:28

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