Having good backups of files is crucial for any computer user since you never know when a crash or hardware failure can strike. A good backup is just as important for your iTunes library as it is for any other files.
There are lots of ways to backup iTunes libraries, but when doing so, you'll probably want to make sure that you also backup your song ratings, playcounts, and other metadata. The technique demonstrated here lets you do that.
Making your backups on a hard drive other than the one in your primary computer is good policy (after all, if your hard drive fails, you don't want your backup to be on the failed drive), so here's how to backup iTunes to an external hard drive.
Begin by plugging the external HD into your computer. Make sure the external drive has enough free space to contain your entire library. Once the drive appears on your computer, launch iTunes.