How To Transfer Time Machine Data to a larger HD that must replace the existent HD.

Problem: Time Machine says current 4TB drive is insufficient and suggests installing a bigger drive.

Okay, I buy a 8TB HD, but I don't want that drive to start with today. I want load the 4TB of data

currently residing on the 4TB drive onto the new 8TB.


How to accomplish is The Question for the Community (prior posts on the same subject fail to describe the "magic handshake" required).


Mac Studio

Posted on Dec 29, 2025 5:09 PM

Reply
9 replies

Dec 29, 2025 6:34 PM in response to Halhoyle

"Magic handshake"? Since you provided very little information about your current Time Machine (TM) backup, I can only assume that your Mac Studio's internal drive is formatted for APFS. As such, TM backups to an existing external drive, cannot simply be copied/transferred/moved to a new drive ... regardless of its size.


Your best bet is to retain your 4TB drive as an archive copy, and start a new TM backup set on the 8TB drive that you are planning to get.

Dec 30, 2025 12:09 PM in response to Halhoyle

Correct! To clarify: You can certainly copy this TM backup to another drive, BUT it will most likely be corrupted doing so as to render it useless for future TM backups. If these backups are important to you, DO NOT use this copy method. In addition, if TM is your only method in your overall backup strategy, now is a good time to re-evaluate that strategy to include additional backup methods.


Ref: macOS Backup Strategy - Apple Community


Again, either retain the existing 4TB drive as an archive OR use it in conjunction with the new 8TB drive (as Grant Bennett-Alder has suggested). Then start a new TM backup to the 8TB drive when you get it.


Dec 30, 2025 7:44 AM in response to Halhoyle

You can also ADD an additional Time Machine backup drive at any time. When you have multiples, every-other backup written goes to every-other drive. Since each drive is a stand-alone backup, either can be removed at any time.


Even if it were possible to copy Time Machine data, you risk introducing additional errors and invalidating your entire backup. Copying Time Machine backups has never been a good idea.

Dec 30, 2025 5:24 PM in response to jjjefff

jjjefff wrote:

Would it be corrupted in the sense that this drive can no longer be used for new backups?

Migrating the TM backup to another drive would not necessary corrupt the drive ... just the TM backup itself.


Will the existing backups also no longer be readable?

That would depend on what exactly you mean. Copying the TM backup from the original drive should not corrupt the existing backup on that drive, only the backup being copied to the new drive.


The bottom line, is with the introduction of APFS, how TM performs backups is very different than pre-APFS where you could just copy a backup to a new drive.


How To Transfer Time Machine Data to a larger HD that must replace the existent HD.

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