Difference between enabling Time Machine's "Encrypt Backups" option, and encrypting from Disk Utility?

Question

I'm setting up Time Machine backups on a new external hard disk.

I chose to first encrypt the disk via Disk Utility:

But I also see these options:

Is there any difference between an "Encrypted" format via Disk Utility and selecting "Encrypt backups" in the Time Machine preferences? What happens if I do both? Or if I encrypt with Disk Utility, but then don't select "Encrypt backups"?

Answer 1

Aha! The answer comes when you try to deselect the "Encrypt backups" option:

So it appears they are one and the same.

Answer 2

The command:

diskutil list my_time_machine_disk_short_name

will confirm you:

#   my_mac:/Users/bob  % diskutil list disk5
/dev/disk5
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                 Apple_HFSX Time_M___disk          *499.4 GB   disk5
                                 Logical Volume on disk2s2
                                 22222222-FFFF-4444-CCCC-AAAABBBBCCCCDDDD
                                 Unlocked Encrypted
#   my_mac:/Users/bob  % 

that Time Machine is using the same technic of logical volume as Disk Utility.

Answer 3

Please note that although both outcomes are the same whether encrypting with Disk Utility or Time Machine, Disk Utility takes significantly longer.

Perhaps this is because it is encrypting the unused free space and TM is not. Can anyone else corroborate?

Also, in Terminal you can simply use this command to show TM volumes & status:

diskutil cs list