mpd configuration with music collection on removable usb disk, using autofs to automount when needed. Used on a RaspberryPi

10-udev-disks.rules

# /etc/udev/rules.d/10-udev-disks.rules
# udev custom rule 

# using # udevadm info -a -p $(udevadm info -q path -n /dev/sda1)
# I found the necessary information about my USB device 
# and take the necessary ones to make it unique (idVendor, idProduct, serial here)

# when plugging the disk, nevermind the device name it gets (sda1, sdb1,...) udev creates /dev/mpd-disk and runs the script indicated
KERNEL=="sd?1",ATTRS{idVendor}=="xxxx",ATTRS{idProduct}=="yyyy",ATTRS{serial}=="zzzzzzzzzzzz",SYMLINK+="mpd-disk",RUN+="/root/bin/hdparm-mpd-disk.sh"

auto.master

# /etc/auto.master
# master configuration file for autofs 

# add a line like this to handle mounting on /media/auto
# the timeout option unmounts the disk if not needed anymore
/media/auto	/etc/auto.media	--timeout=60

auto.media

# /etc/auto.media
# specific autofs configuration file to handle /media/auto automouting

# mounts /dev/mpd-disk on /media/auto/mpd-disk
mpd-disk	-fstype=auto	:/dev/mpd-disk

hdparm-mpd-disk.sh

#!/bin/sh

# if you want to use idle features of your usb disk, check hdparm documentation with man hdparm
# in my case this checks the power status
hdparm -C /dev/sda

# and this sets idle timeout as 2 minutes
/sbin/hdparm -S 24 /dev/mpd-disk

mpd.conf

# /etc/mpd.conf
# mpd configuration file

# only relevant directives noted here

# the music directory stays as default, this way when mpd starts but no music plays the usb disk is not mounted
music_directory		"/var/lib/mpd/music"

follow_outside_symlinks	"yes"

follow_inside_symlinks		"yes"

terminal

# commands to use

# create a link to the real music collection
cd /var/lib/mpd/music
ln -s /media/auto/mpd-disk/Music Music

# make the script executable
chmod u+x /root/bin/hdparm-mpd-disk.sh