When I bought hard drives for my server I searched around and decided to buy Western Digital green power disks. I bought 3 750GB disk and set them up in RAID 5 so that I would have some security. I installed smartmontools and added the following lines to /etc/smartd.conf: /dev/sda -a -d sat -o on -S on -s (S/../.././01|L/../../6/02) -m myemail(at)nospam.dk /dev/sdb -a -d sat -o on -S on -s (S/../.././01|L/../../6/02) -m myemail(at)nospam.dk /dev/sdc -a -d sat -o on -S on -s (S/../.././01|L/../../6/02) -m myemail(at)nospam.dk /dev/sdd -a -d sat -o on -S on -s (S/../.././01|L/../../6/02) -m myemail(at)nospam.dk sda being my OS disk and sd[abc] being my storage disks. I thought everything was fine with this until I started pondering the other day why the hard drives never went into standby mode. server:~# hdparm -C /dev/sd[bcd] /dev/sdb: drive state is: active/idle /dev/sdc: drive state is: active/idle /dev/sdd: drive state is: active/idle I then started trying to setup hdparm to spin down the drives after 10min of inactivity. But for some reason it did not work. I searched and searched on Google trying to come up with a solution to the problem until I finally stumbled on a post somewhere where a person mentioned that spin down on his/her Western Digital disks didn't work until he had set up smartd and done a short test on the drive. I ran a short test on the drives but this didn't solve the problem but in the process I found that smart tests had never been run on either of the drives. I pondered this for some time and looked into it and finally I realized that if /etc/smartd.conf has a line starting with DEVICESCAN all other device lines are ignored. I commented out the DEVICESCAN line, restarted smartd and waited until next day. Voila, all of a sudden my disks had spun down as I had requested. I checked up on the specifications of the drives. According to Western Digital the green power disks use 2.8 watts in idle and 0.40 watts in standby. 3 disks * 2.4 watts = 7.2 watts. 7.2 watts * 24 hours/day * 300 days/year = 51840 Wh/year or 51.8 kWh/year. This equals to roughly DKK 100,- per year. This may not be a lot but DKK 100,- saved here and another there will sum up pretty fast, and it didn't really cost me anything except for some time to fix it. Besides I like being a nerd like this. I enjoy it tremendously.