Continuing Time Machine backups on a new Mac

> What you mean with “it won't get any more updates”?

Imagine the scenario where you have OldMac (now retired) and NewMac (bright and shiny).

Let's say that your old Time Machine backup of OldMac has 100 snapshots going back 3 years, from November 2023 though November 2026. These backups consume 1TB of the 2TB drive (fill in your own numbers :) )

You connect this drive to your NewMac and do not inherit the old backup:

The OldMac backups will stay as they are. They will consume 1TB of storage, and will not grow while this drive is connected to NewMac

The space used will also never shrink - since it's not active, Time Machine will not cull old backups to make space.

Therefore you have 1TB of space for new backups of NewMac.

If the drive fills up (1TB of old backups for OldMac, and 1TB of backups for NewMac), then TimeMachine will only delete data from NewMac's backups to make room for new data, since it isn't allowed to touch OldMac's data.

Note: the above changes if you keep OldMac running and periodically connect the drive to OldMac - Time Machine will append new data to this backup, as well as clean old ones as needed. You essentially have two backup streams on this drive.

Alternatively, you connect this drive to NewMac and do inherit the old backup.

Now Time Machine considers the three years of old data as relating to this NewMac. Any file changes to NewMac will be appended to the existing three years of backups, and you can restore any of that 3-year old data onto NewMac.

In this scenario, the drive can NOT be connected back to OldMac (or, more specifcally, you can connect it, but it won't act as a Time Machine backup for OldMac, since the backup stream is now 'owned' by NewMac).

So the choice depends on what you want to do with that backup data. If you want to keep OldMac running in parallel, then you may want to keep a separate backup stream for it. If your goal is to retire OldMac, then it might make sense to inherit the history.

In summary, you have three options:

1) Run OldMac and NewMac in parallel, each with their own Time Machine backup -> Do NOT inherit, and periodically plug the drive into each Mac to run the backup

2) Retire OldMac, but keep a copy of its data intact for posterity/archive/trus purposes -> Do NOT inherit, and leave the old backups as-is

3) Retire OldMac and never look back -> DO inherit - OldMac's data will be considered part of NewMac's until the backup drive fills up and Time Machine needs space.

Does that help?

If you opt to inherit the old backup on the new machine, then Time Machine will act as if the backup files are for the new machine, and it will continue to add files to the backup, and you can recover files from the earlier backups, even if they, technically, are older than this machine.

If you start a new backup sequence, then Time Machine will leave the old backups in place and start a new backup sequence for the new machine.

The difference is really whether you want to lock the old machine into a historical record (it won't get any more updates, but also old files won't get deleted), or whether you want to use the old backups as if they'd been part of the new machine's history all along.

Thank you very much for your support.

What you mean with “it won't get any more updates”? Does it mean that if connected to the old Mac it won’t do any more TM shots for that Mac but it will only work on the new one?

Also, are the old TM backups going to be delayed as standard when there is no more space on the backup drive?