"Test 1: Who is spinning up the disk Not everyone has an SSD in
their system yet (I feel sorry for those who don't). The mechanical
rotation of a disk seems to cost in the order of 0.5 Watts to 1
Watt of power (depending on the disk).
"For this reason, pretty much all laptop disks will stop
spinning after several seconds of inactivity.
"Now, to enjoy this power savings, it is essential that the disk
gets to actually spin down, that is, that there are long periods of
inactivity. In a typical Linux distribution, there are various
programs that, unfortunately, write things to the disk all the
time. Until now, the only way to find out which programs were doing
this was to use the blockdump kernel feature."