I read that link and it looks like @PascalLieb asked a similar question. The accepted solution by @SteveNV does not seem to really answer the question.
The question is about “correct way to shutdown” “without damage of attached devices such as external hard disks, etc.”
@SivaRamaKrishnaNV you said “There is no way to shut down the board from a Tegra” - in the context of your response, it seems like you mean “There is no way to poweroff the board from a Tegra”. Also, you said “Aurix poweroff is the only way to power off the board” - well it is easy to power off the board by pulling the battery cable, but that seems unsafe.
So the back to the question about “correct way to shutdown”.
Could you please confirm if it is safe (no loss of data, no filesystem inconsistencies) by just issuing an aurix poweroff command. Or, could you please confirm if it is actually necessary to login to Xavier A and Xavier B separately, shutting down the operating system first, before issuing an aurix poweroff.