What would be a proper way to shutdown a sata disk connect with a usb interface ?

[Guy Gold]

Hi Boris,

After you're convinced all data operations have stopped, udiskctl is
useful to logically detach the drive, one last step before physically
powering off.
e.g
udisksctl power-off -b /dev/sdc

>From  "man udisksctl"
power-off
Arranges for the drive to be safely removed and powered off. On the OS
side this includes ensuring that no process is using the drive, then
requesting that in-flight buffers and caches are committed to stable
storage.


-- 
Guy Gold