Can Time Machine back up an internal drive when you are booting from external drive?

[levmc]

I am booting Mojave externally for my MBP, and I would like to do a time machine backup for the internal OS. Is that possible?

 

[James_C]

As Time Machine can backup can backup external drives, then if you are booting from an external drive it should be able to back up an internal drive. Just make sure the internal drive is not excluded from the time machine backup. Go into options in Time Machine preferences to make sure it is not excluded.

Time Machine can't backup anything else on the drive that the Time Machine Backup is stored on. I am assuming that you have a separate Time Machine External drive.

 

[levmc]

I made a Time Machine Partition on the external for the purpose of backing up that internal drive. Would that work?

BTW I don't want to back up the external Mojave, just the internal drive.

 

[James_C]

Yes that should be fine, provided the external drive is Mac OS Extended (Journaled) format.

 

[levmc]

When I click on "Select Backup Disk..." does it mean that I'm selecting the disk that I want to back up, or the disk that I want to back up to?

 

[James_C]

Its the disk that you want to store the Time Machine Backup on. Make sure you select the correct partition!

 

[levmc]

Then where can I select the disk that I want to back up? (Otherwise how do I know this is just going to back up the bootable partition which I am running the Time Machine on?)

 

[James_C]

Time Machine will back up all internal disks by default and exclude any external drives by default. just check the options in system preferences for time machine, and make sure the internal drive is not in the excluded list.

 

[levmc]

The TM is backing up right now and it says: "Backing Up: 31.88 gb of 228.71 gb"
When I look at my internal drive storage space, it says "Capacity: 250.14 gb. Available: 47.77" (about 202 gb full)
So if it was only backing up my internal drive, it should say "X gb of 202gb" instead of 228.71 gb, so wouldn't this be actually backing up both the internal drive and also the external partition that I'm using to boot the MBP right now?

If I tried to restore the TM backup to an empty internal drive, which backup would it restore? The 202gb of internal drive or about 26gb of the external partition? Would it give me choice as to which backup I want to restore?

 

[James_C]

If I tried to restore the TM backup to an empty internal drive, which backup would it restore? The 202gb of internal drive or about 26gb of the external partition? Would it give me choice as to which backup I want to restore?

If you have a complete system disk failure (your current external drive) you would need to use Migration Assistant ( which will be an option given to you when you restore MacOS on your external hard disk). You can also run Migration Assistant after you restore Mac OS. Migration Assistant will only restore your system hard disk (Your current external hard disk), I don't think it will automatically restore your internal hard disk. However you can go into Time Machine and restore all your files to your internal hard disk.

I put together a short screen cast that shows you how you can check what Time Machine is backing up and how you can selectively restore folders on your hard disks.