3.1.3.1. ...stopping the hard drive motors when the drives are not in use?
The hdparm program can be used to stop a drive immediately or to configure it to stop if it is idle for a certain length of time; this is called a spin-down (and restarting the drive is called a spin-up ). This does save some power; however, the drive is rarely idle for very long and the length of time (and amount of energy) required to spin-up the drive is significant (and hard on some hardware), so opinion is divided on whether it makes sense to use this feature.
In the case of a two-drive system where the second drive is rarely used, an idle spin-down timeout is a good idea. Configure it with the hdparm command:
# hdparm -S 6 /dev/[hs]d[a-z]
The -S option configures the amount of time that the drive must be idle before spin-down is triggered. The scheme used to encode the timeout period is a bit convoluted (it is described in detail on the manpage for hdparm ), but 0 means that spin-down is disabled, and a value from 1 to 240 sets the idle timeout in multiples of 5 seconds (5 seconds to 20 minutes). The value of 6 used here indicates a 30-second idle timeout.