I don't think there is anyway of telling, apart from temp and drive noise.
My 343 is around 42-44C at the lowest (It is currently summer here). I have 4x 1.5TB in RAID 5, but I think the sleep function works. As I can hear the drives spin back up, if I access my unit after a period of inactivity, sounds the same as when I turn on the unit.
But I don't think there is a actual way of the unit notifying you on the state of the drives. Could be a feature request?
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