Mac Studio: Migrate from two Time Machine drives and reuse

You will need to only connect one drive at a time to restore. Once the one drive is done you can connect the other and migrate that data. It will only add unique files that are different. You can continue to use those drives but I would only use drives formatted to APFS. If all OK I would probably erase all TM drives and start a new backup.

<< Files are shared on both it seems.>>

Generally speaking, when you ADD an additional drive to Time Machine, it starts a NEW stand-alone backup on the new drive, starting the day it was added.

If both drives are still connected, every-other backup goes to every-other drive.

So each drive would be expected to contain the most recent copy of your files, and they should differ mostly in how far back the (unique) old files go.

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when you migrate from a Time Machine backup, or do so at first run using Setup Assistant, you are supposed to be offered the ability to "inherit old backups".

My recommendation is to connect ONLY the backup drive you want to CONTINUE to use going forward as the source of backup files. and say yes to "Inherit backups"

Since to older drive is much smaller, it is unlikely to have very many unique files not already on the larger drive. Older backups are consolidated as space gets tight.

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