Can I combine Time Machine backup drives?

Read the Full Disclaimer

" 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.

I'd not fuss with backup drives. Instead, start a fresh new backup on another drive(s). Put the old backup drives to rest for a few weeks/months and re-cycle them when you don't miss anything from them.

jjjefff wrote:

I have three external hard drives that were used for Time Machine backups. If I copy them over to one, will the backups still be accessible?

It is not possible to Copy a Time Machine Backup to another drive - Full Stop

Not even a dedicated cloning software can do that

Follow the advise by @ Matti Haveri and mothball the drives for future usages

Can I use CCC to copy a Time Machine backup?

jjjefff wrote:

The link suggests that backups can be copied using Finder?

Prior to Apple introducing the APFS format, Apple used HFS+. Time Machine (TM) backups of a HFS+ internal drive can simply be copied from one external HFS+ formatted drive to another.

Now with APFS, this is no longer possible. The following article (and a number more from the same author) goes into great detail about this ... and I would suggest you give them a read when you get a chance. This will go a long way to address the "why" you can't simply copy TM backups going forward.

Ref: What can you do with Time Machine backups on APFS? - The Eclectic Light Company

Hi jjjefff

Yes HFS to HFS.

I used SuperDuper and it copies a working TM backup. Takes several hours for a large ones.

Carbon Copy Cloner won't

I haven't tried multiple ones on same target hard drive. Might work on different partitions. No harm in trying - just time consuming.

jjjefff wrote:

I understand all the information points to it being impossible.

I'm just wondering... if I copy the partition, how could it not work? Shouldn't the copy be a clone of the original?

From the previously-linked info: “It’s possible but complex to make a block-level copy of an entire disk at the command line.”

Go try whatever you want to try here of course, and let us know.

Pragmatically, I’d do a block copy into a zip archive or such. Something akin to this:

dd if=/dev/srcvol of=/srcvol.img
zip srcvolcompressed.zip srcvol.img

Whatever you do try, also unpack (unzip) it and test it with Time Machine, before disposing of the original storage.

I’d update from macOS 15.0 first, though.

Owl-53 wrote:

“It is not possible to Copy a Time Machine Backup to another drive - Full Stop”.

Not strictly correct as I have copied Sequoia (and previous MacOS) TimeMachine backups successfully and continue to use on the copied drive.

The caveat is the TimeMachine backup drives were formatted HFS not AFPS – yea you can arrange a TM backup of Sequoia on HFS formatted drive.

With the software I have I suspect I would not be able to copy >1 backup to a single drive as the OP wants to do.

I have not tried if the drive is formatted APFS but I can imagine copying might not work.

To reinforce matters

https://discussions.apple.com/thread/256219254?sortBy=oldest_first

"Magic handshake" ?

There have been numerous cautions regarding the usage of HFS Journaled drive formatting with Time Machine Backup Utilities

Forcing TM Backup Utilities to use an Unexpected Drive Format ?

Actions have consequences that may not always be immediate.

When these repercussions eventually emerge, they are often unexpected.

Prcceed at you own peril

Hi Jjjefff

It is great that you are still wondering.

Not “all the information”. I can assure you without any doubt that I have copied successfully every time using the method I described with HFS formatted drives.

Can’t remember if drag and drop “Backups.backupdb” works but might at least have access to old files. No harm to try.

Best thing to do is try whatever method takes your fancy. You might find it (APFS formatted) TM might not work as a TM backup but you may be able to extract files manually which is better than nothing. (After all if it is from an obsolete Mac then ‘starwars’ extraction wouldn’t work on a later Mac anyway).

As an additional precaution turn off TM backups while you do the copying just in case that interferes with the process.

I’ll see if I can do further experiments.

Don't give up (yet)