Pros and cons of claiming Time Machine backups on a new MacBook

kiki453423 wrote:

I bought a new macbook and wondering the pros vs cons of "claiming the existing back ups" from my Time Machine on the new macbook or creating a separate backup.

I always start a new backup on a new backup drive. And keep the old backup to continue using with the old Mac, which we tend to keep.

One advantage of inheriting the previous Mac's backups is that you can maintain some continuity if you think you might need to retrieve an older version of an older Mac file sometime for the new Mac. I never have needed to do that and prefer to start fresh, but your situation may be different. However, as noted below, older backups will have to be deleted sooner since the inherited backup drive will fill up faster. Also, if you no longer have the old Mac, you might save a little money by continuing to use the existing backup as you can delay getting a new backup drive.

Disadvantages of inheriting the old backups:

• You can't use that backup drive with the old Mac anymore.
• The backup drive may be closer to full due to having been used previously for backups with the old Mac. This means it may fill up sooner or older backups will have to be deleted to make more room. Also, if the backup drive is close to full, the backups will run slower.
• An older drive may be less reliable in the long run. Starting with a new backup drive probably means the new one will last longer.

Advantages of not inheriting the old Mac backups:

• Fresh start with a new backup drive, with maximal space available. Newer backup drive is likely to be longer lasting and more reliable than the old one.
• Keeping the old backup while starting in with a new one means you can go back to the old one in the future to get something from an old backup as needed. And all the old backups will be there.
• You can also continue using the old backup drive with the old Mac.

Apple offers these options -- you won't go wrong with either option but you can see that choosing one or the other may provide something that is of value to you.

There is a corollary to the accurate and comprehensive replies already posted. Inheriting the existing backups when asked is generally a good idea — unless — it is that Mac's only backup drive.

The reason is that TM guarantees an absolute minimum of one and only one completely restorable system backup. The very first incremental backup created subsequent to any large change to the source volume's contents may just be large enough to cause TM to delete all previous backups. Potentially years worth. It will delete them only after completing the one and only one completely restorable system backup it guarantees. Users who erroneously assume TM is an archival system (which it has never been) tend to complain when it does that, conclude TM is no good, the latest macOS version broke it, etc.

Another reason is that if you choose to create a new backup on that same backup device, it is unlikely to have sufficient space. With the passage of time TM will eventually claim all of a backup drive's capacity, leaving only enough to create an additional incremental backup, after which older backups get deleted. Meanwhile, the existing backup remains untouched. It will be off limits, so TM won't be able to do that. The only way to resolve that problem will be to erase the entire backup drive.

One and only one backup drive does not comprise a comprehensive backup strategy anyway. Get more, if for no other reason that any device can fail at any time. TM will use as many backup drives as you wish to provide.

There is one more case in this set of options.

Time Machine is happy to have MULTIPLE different back drives connected.

When there are more than one, each is an independent backup starting from when it was connected, and any drive can be removed at any time. When writing to the disk, it cycles through the available disks.

So you could:

claim/inherit your existing backup AND

add an additional (likely larger) backup drive.