I have an SSD that houses my Debian desktop environment. I don't want things like logs chewing through it's life, so I moved the logs to a mounted drive.
The following assumes you already have the harddrive you want to utilize mounted via /etc/fstab
as the /storage
directory.
Switch to super user
su -
Stop the rsyslog daemon, so no logs are written (and subsequently interrupt the switch)
service rsyslog stop
Make a new directory for the logs, on the mounted /storage
drive
mkdir -p /storage/log
Move the original log directory into its new home on the 2nd harddrive
mv /var/log /storage/log
Symlink it, so you don't have to edit a bunch of system config that expects /var/log to exist
ln -s /storage/log /var/log
That's it.
mkdir /storage/Downloads
Symlink Downloads, too
ln -s /storage/Downloads /home/angela/Downloads
Easy.