how to overwrite backup

sawwhetowls wrote:

how do I set my back up to overwrite what's already on the back up drive

You don’t. Time Machine is an incremental backup app. When it runs it backs up any file that has changed since the previous backup. When space runs out on the back device Time Machine automatically deletes the earliest backed up files to make room for the current backup. It’s automatic and the user has almost control over how it works. As others have pointed out if you want older files to overwritten your only option is erase the Time Machine volume and start over. There is no option to overwrite current files.

And overwriting what’s already there completely defeats the purpose of the incremental process. With Time Machine you can restore previous versions of a document that have been changed over time, for example, or restore software you had previously deleted.

Depends on what kind of backup. The typical way is to reformat the backup volume, which will wipe it. Then start over again. I’ve done that with bootable backups cloned with Carbon Copy Cloner as well as Time Machine backups.

if we are talking about Time machine:

Time Machine may spend all afternoon making your first full backup. You can continue to do your regular work while it does this. The first Full Backup is by far the biggest backup. After that, it will work quietly and automatically in the background, without interrupting your regular work, and only save the incremental changes.

Time Machine's "claim to fame" is that it is the backup that gets done, because it does not ruin performance of the rest of the computer while doing its backup operations. You do not have to set aside a "Special Time" when you only do backups. When you need it, your Time machine Backup is much more likely to be there.

Time machine has the ability to restore a full-backup equivalent at any point still in its backup set. Over time, individual backups are consolidated to reduce the total space required, so intermediate versions will be removed.

So in ordinary use, you do not need to endure "all afternoon" full backups except at the start of a new backup set, and the increments are added to the backup set as you continue to use Time Machine.

If you want to "start over" just ERASE the drive.

lkrupp wrote:

You don’t. Time Machine is an incremental backup app. When it runs it backs up any file that has changed since the previous backup. When space runs out on the back device Time Machine automatically deletes the earliest backed up files to make room for the current backup. It’s automatic and the user has almost control over how it works. As others have pointed out if you want older files to overwritten your only option is erase the Time Machine volume and start over. There is no option to overwrite current files.

It might be possible to delete older Time Machine directories by date. But these are incremental and each new backup (by time) builds up using previous incremental backup directories. I don't believe it's possible with the latest version of MacOS. I wouldn't recommend it though. I'd think it might corrupt the volume to do that.

NEVER use Finder to modify anything on a Time machine backup drive. Your entire backup set can lose its integrity and become useless.

You can ask Time Machine to remove a specific old back-up, but this generally does not produce more than a tiny amount of reclaimed space. It can take time machine quite a while to consolidate one backup, and it will not accept a request for more until the first one is consolidated.