how to erase a timemachine drive

First of all, that’s not expected behavior. Time Machine deletes older backups to make room for newer ones. You should never run out of space on a Time Machine drive.

As for erasing you should first remove the drive from Time Machine’s list of available drives.

System Settings->General->Time Machine-> select the drive the click the minus (-) sign to remove it.

Use Disk Utility found in the Utilities folder to erase and reformat the drive.

You cannot transfer the files to a new drive. You need to erase and start over or save the old drive and start a new one. TM may stop backing up if your internal drive is full.

Here's one:

You use a Virtual Machine Manager (VMM), like Parallels, and have created one or more VMs with it. Everytime you access one of these VMs, it changes, and TM will try to back up the entire VM. These could be multiple GBs in size and can quickly "overwhelm" the backup drive ... especially if that drive was not adequately sized to start with. That is, the user has, for example a 1TB internal drive on their Mac, and use TM to back up to a 1TB external drive.

lkrupp wrote:

First of all, that’s not expected behavior. Time Machine deletes older backups to make room for newer ones. You should never run out of space on a Time Machine drive.

FWIW, that's actually not the case. There are circumstances where Time Machine cannot delete older backups to make room for a new backup.

In all my years of using Time Machine not once have I been notified that backups cannot take place because it’s full. Under what circumstances might this happen?

I've never seen it either, but all of my backup drives are three times the size of my data.

As Tesserax mentions, it happens most often when someone purchases the same size external for Time Machine as the internal drive. It's one of the reasons a two times or larger drive is recommended. I'm surprised you haven't seen the posts of people who couldn't back up to Time Machine.

In all my years of using Time Machine not once have I been notified that backups cannot take place because it’s full. Under what circumstances might this happen?

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