I have built for myself a simple Media Center, based on Zotac ZBOX ID41 Plus, XBMC-Live, Transmission, Flirc and other useful stuff. The idea is having a low-energy consumption machine that I control with a remote. And it has to be always on.

One thing I was concerned about is how to deal with my external HD connected to it: I’m of course expecting those to eventually fail if they are always spinning.

Well, a bit of scripting and cron can go a long way. Here is my solution.

Step 1: dependencies

Just install sdparm and you should be all set, at least on a “normal” Linux box where Cron is already configured.

Step 2: scripting FTW

Put a script like this somewhere in your system. I have it in my ~/bin:

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# !/bin/sh

# Only ROOT can run this
if [ "$(id -u)" != "0" ]; then
        echo “This script must be run as root” 1>&2
        exit 1
fi

STATE_FILENAME=state_$1.spindown
PREV_STATE_FILENAME=prev_state_$1.spindown

# Get new state from diskstats
NEWstate=$(cat /proc/diskstats | grep $1)
echo $NEWstate > "$STATE_FILENAME"

# compare md5 sums
md5new=$(md5sum $STATE_FILENAME | sed 's/ .*//')
md5old=$(md5sum $PREV_STATE_FILENAME | sed 's/ .*//')

# if no changes, power down
if [ "$md5new" = "$md5old" ]; then
        sdparm --flexible --command=stop /dev/$1 &>/dev/null
fi

# Write current state to file
echo $NEWstate > "$PREV_STATE_FILENAME"

A very basic and simple one, isn’t it? What it does is just probe /proc/diskstats virtual file to get info about the recent activity of a disk. If it has not changed in the last 30 minutes, than it’s time to use sdparm to send a stop command --command=stop. That’s it.

Step 3: Cron-it-up!

Add the following lines to your /etc/crontab:

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*/30 *   * * *   root   sh /home/xbmc/bin/spindown/spindown.sh sda
*/30 *   * * *   root   sh /home/xbmc/bin/spindown/spindown.sh sdb
*/30 *   * * *   root   sh /home/xbmc/bin/spindown/spindown.sh sdc
*/30 *   * * *   root   sh /home/xbmc/bin/spindown/spindown.sh sdd
*/30 *   * * *   root   sh /home/xbmc/bin/spindown/spindown.sh sde

The above lines execute the script against sda, sdb, sdc, sdd and sde.

That’s it. I have been using this method for almost 2 years not, and thought it might be helpful to others.