Receiving power isn’t the same as being “on”. I’d assume the drive has a sleep state that it goes into after inactivity, and those hours don’t count as “power on” hours.
Interesting, thanks. The spec does leave it almost uselessly underspecified:
"Power On Hours: Contains the number of power-on hours. This may not include time that the controller was powered and in a non-operational power state."
The same drive reports only 329 "controller busy time" minutes.
