I use a limited capacity external drive for backup with Timeline and it routinely expels oldest data to make room for new; I propose to maintain that while hooking up a 1T drive on which to store memorabilia data for posterity, much of which will be scanned. Can I operate with both externals in operation using two USB ports, or possibly using a USB 3 hub in order to thereby keep one of the computer's USB's ports available for other uses?
MacBook Pro 13", macOS 10.14
AS others have said, you can use both at the same time but you've indicated that the original TimeMachine drive is full. In that case you really should consider two options. 1) retire it. Put it aside for a period of time (say 6 months) in case you need to restore a file from it. When you feel you'll no longer need to restore to one of those old files, use the drive for something else. 2) copy the contents of the older drive to the new one. See Apple's instructions here: https://support.apple.com/en-us/HT202380
AS others have said, you can use both at the same time but you've indicated that the original TimeMachine drive is full. In that case you really should consider two options. 1) retire it. Put it aside for a period of time (say 6 months) in case you need to restore a file from it. When you feel you'll no longer need to restore to one of those old files, use the drive for something else. 2) copy the contents of the older drive to the new one. See Apple's instructions here: https://support.apple.com/en-us/HT202380
If you provide an additional drive AND tell Time Machine to use it as well, Time Machine will create a separate, stand-alone backup set on the new drive.
Backups will then alternate on the drives -- every other backup will go to every-other drive -- supplying and removing whatever is needed to keep each drive as its own stand-alone Backup set.
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if you do NOT specify the second external drive as a Time Machine Backup drive, you are free to use it for whatever you wish, whenever you wish.
Can I operate with both externals in operation using two USB ports, or possibly using a USB 3 hub in order to thereby keep one of the computer's USB's ports available for other uses?
Yes, you potentially can do either.
You can use several external drives at the same time.
Use two external drives?
