Spins down an idle disc. Made for raspberry pi raspbian wheezy, and my external usb drive which spins down with the command "sg_start -r -S".

zzspindown

#!/bin/sh
#spins down a disk. put this in /etc/cron.hourly so that it runs last
#cronjobs are run in alphabetical order so zzspindown is a sure bet...
#licence: public domain

DISK=sda

SGSTART=/usr/bin/sg_start
if [ ! -x $SGSTART ]
then
  echo "$SGSTART missing. aborting."
  exit 1
fi

PREVIOUS=/run/.spindown-$DISK

#to prevent errors from the first run, create the file
if [ ! -f $PREVIOUS ]
then
  touch $PREVIOUS
fi

# Then see if there's activity in between this run and the previous run.
# If not, spin down.

line1=`cat $PREVIOUS`
line2=`grep " $DISK " /proc/diskstats`
echo "$line2" > $PREVIOUS

if [ "x$line1" = "x$line2" ]
then
  $SGSTART -r -S /dev/$DISK
fi

exit 0