I cannot unmount and then reformat a former time-machine disk (size 2TB]

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Level 1

36 points

I cannot unmount and then reformat a former time-machine disk (size 2TB]

I bought a new TM disk because the old was dropping out occasionally for some reason; and I got errors.

Now I want to re-use the old drive.

But I cannot un-mount the drive, the first step that is needed for reformatting (or at least give me the hope of reformatting):

I saw these steps:

1) unmount

2) erase the TM partition

3) erase the logical volume group in which the old TM exists

The disk cannot be unmounted <It is "in use">; and trying to nevertheless erase stops in error codes.

How can I solve this? The drive is a 2TB Blue drive, so it is quite some value.

I tried to delete separate BU folders (500TB, 18 in total from 2024) and say 'delete immediately', they disappear from the list but are back a day later.
But even then the disk is 'dedicated' and when I add a file the deletion of such a file is nearly impossible too. It also cannot be deleted, ergo I cannot even use the 1.5TB remainder of the SSD.

Support said leave it on; well it is on for weeks, no avail.

I have an idea: should I "activate this disk again for TM"? My Studio might erase what is on it? After which I could regularly unmount/erase? [I have no trust in my own steps, been on this too long.]

Posted on Jun 6, 2025 4:51 AM

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Answer 1

dialabrain

Level 10

132,359 points

Jun 6, 2025 5:29 AM in response to alberti-nl

FWIW, the drive has to be removed from the Time Machine settings before you can erase it.

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Answer 2

John Galt

Level 10

151,842 points

Jun 6, 2025 1:05 PM in response to alberti-nl

I bought a new TM disk because the old was dropping out occasionally for some reason; and I got errors.

Now I want to re-use the old drive.

If that disk kept failing repeatedly it seems to me depending on it may be unwise. In any event you ought to be able to erase it using Disk Utility. If that disk had been partitioned as your question implies, be advised that's not a good idea for a number of reasons. Erase the entire device. We may no longer selectively erase individual backup files. Even when we could it tended to corrupt the backup, rendering it unreliable at best, and requiring that the entire device be erased for continued use.

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