desired disk doesn't show up in list of available disks for Time Machine

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desired disk doesn't show up in list of available disks for Time Machine

I am configuring a new, Big Sur-enabled M1 iMac to back up (via Time Machine) to a new 6 TB external hard drive that came pre-formatted with APFS. I have left the hard drive with the one partition it had when it arrived, but added 2 additional volumes to the one container on that partition -- one for Time Machine and one for SuperDuper! duplicates. But, when I click on "Select Backup Disk ..." in System Preferences > Time Machine, neither of those volumes appears as options. How can I get them to show up?

iMac 24″, macOS 11.6

Posted on Jan 17, 2022 11:20 PM

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Answer 1

Barney-15E

Level 10

116,140 points

Jan 18, 2022 2:18 AM in response to keithlantz

I don’t believe you can assign a volume you create in Disk Utility to Time Machine. I couldn’t, though thought it should be possible. You have to partition it.

There are as a post about using diskutil (Terminal) to set a quota and mark the volume as Time Machine because it didn’t work in Disk Utility. I couldn’t find the post.

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Answer 2

keithlantz Author

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Jan 18, 2022 10:59 AM in response to Barney-15E

Yeah, I assume this can be addressed with diskutil, but have been unable to determine the precise command to invoke. I know I need to set the "role" for the volume to "T" (for Time Machine), and I already used Disk Utility itself to set quotas, but I'm not sure what else I have to do -- if anything.

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Answer 3

keithlantz Author

Level 1

5 points

Jan 18, 2022 11:25 AM in response to keithlantz

Addendum: Since I currently have nothing I need on the disk in question, I went ahead and tried the following (in Terminal):

diskutil APFS changeVolumeRole disk5s2 T

I then ejected the disk, restarted it and, voila, the desired Time Machine volume now appears with the Time Machine icon. But ... when I click on "Select Backup Disk ..." in System Preferences > Time Machine, it still doesn't show up. So there is something else that needs to be done. Ideas?

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