Disk Encryption of External sda in jatson AGX xavier(RS32.7.1 js4.6.1)

Hello ,thank u so much
Now I can success to boot the encrypted external SSD .
I am curious about the matter that what the different between encrypted external and encrypted internal . And when I finish flashing the encrypted external SSD,then boot .It seems I dont need modify initrd to unlock additional encrypted file systems.They are all mounted on mapper.