How to migrate Time Machine backups from old external drive to new?

Ukiman0714 wrote:

First off, I should mention that my new drive is split into two partitions / volumes. One for Time Machine backups and another for regular file storage, each 1 TB in size.

Echoing what others state that it's recommended to dedicate a drive to TM backup. Having said that, it's certainly possible to have more than one use, from a technical standpoint.

Note that there is a difference between a volume and a partition for an APFS formatted drive (which is what you should use for TM). A volume is a variable-size section of the container, so if you have two volumes on an APFS drive and one is for TM backup, that volume can expand to take up more space as needed for TM, meaning less space for other file storage. The solution to that is to limit the size of the TM backup when you set it up.

The other option is to partition the drive. Partitions are fixed sizes and for APFS they are separate containers. That's likely the better option for a drive used for TM backup and file storage, or for TM backups of multiple Macs. Personally, I use a pair of 4 TB SSDs as TM backups for 5 Macs in the house, where each has it's own partition based on the size of that Mac's internal storage.

The rationale for not using an external drive for both TM backup and file storage is not technical, it's practical. There are two types of drives – those that have failed and those that have not failed yet. The reason for a backup is so you don't lose data when they do. If the external drive you use for a TM backup is also being used to store files so they don't take up room on your internal drive, and that external drive fails, then you've lost your only copy of those data.

A commonly recommended strategy is 3-2-1 where you have three copies of your data, two of which are backups and one of which is stored offsite. That pair of SSDs I mentioned above are my secondary backups and I have two of them so that I can swap one offsite (to my desk in the office) each week. My primary backup for those 5 Macs is a Synology NAS with 2 x 10 TB in RAID1. That has 6 shared folders (functionally equivalent to partitions), 5 for the TM backups and one for a general file share. That file share is in turn backed up to another set of SSDs that are also swapped offsite weekly. So really, my setup is 5-4-1 for data on the Macs and 4-4-1 for data not on the Macs (because there are already 2 copies on the RAID1 NAS). Overkill? Maybe, but I won't lose any data if a drive fails, and if the house burns down with all the devices in it then at worst we'll lose no more than the most recent 2 weeks of data.

Moving existing backup sets from and old external drive to a new one seems like it should be a built-in function of Time Machine. 😢

As for what you want to do, Owl-53 gave the simple, clean answer – not possible. The way TM is coded, you cannot move the backups from drive to drive. If you want your backups on a new drive, you need to start over on the the new drive. You can keep the old one as an archive and access it later via the TM browser.

Ukiman0714 wrote:

I also tried just opening Time Machine settings and adding the new drive, which it did successfully, but there doesn't seem to be a way to move old backups to the new drive.

Hoping for some help and guidance. Moving existing backup sets from and old external drive to a new one seems like it should be a built-in function of Time Machine. 😢

That's correct— the inheritbackup function is no longer applicable in the contemporary macOS, independent of your ChatGPT regurgitater.

The recommendation is start a new backup going forward.

If you value your user data

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

More than one device, more than one backup methodology— and backup regularly.

For your interpretation "seems like it should be..." submit your Apple Feedback here: Product Feedback - Apple

Q - " How to migrate Time Machine backups from old external drive to new?"

A - Not possible

https://support.bombich.com/hc/en-us/articles/20686476880791-Can-I-use-CCC-to-copy-a-Time-Machine-backup

" No. Copying a Time Machine backup volume with anything other than the Finder is not supported (by us, nor Apple); CCC specifically disallows copying anything to or from a Time Machine backup volume. Apple does not document a procedure for making copies of Time Machine volumes. "

Ukiman0714 wrote:

First off, I should mention that my new drive is split into two partitions / volumes. One for Time Machine backups and another for regular file storage, each 1 TB in size.

For what it's worth, it is recommended you use a dedicated drive for Time Machine, and not split it into volumes for other purposes.

dialabrain wrote:

Ukiman0714 wrote:

First off, I should mention that my new drive is split into two partitions / volumes. One for Time Machine backups and another for regular file storage, each 1 TB in size.

For what it's worth, it is recommended you use a dedicated drive for Time Machine, and not split it into volumes for other purposes.

+1