Benchmarks: Power Consumption
A four-bay server carrying the hardware of the DS6100 is bound to consume more energy than your average NAS, though 69 watts under load wouldn't be considered too big a burden when servicing up to 50 client machines.
Windows Server, as far as we can tell, doesn't include support for hard-disk spin down after a period of inactivity. Such a feature is nice to have on a home NAS, but we suspect it won't be missed on a business server that's designed to be frequently accessed by multiple clients.