put it all on a separate hard drive for 2 reasons -1. Obviously, so you've got all your stuff if you lose your laptop and 2. to free up space on your main computer - computers run slower the more stuffs on em. I've got far more movies and music in Itunes than my computer can store, so I have a separate hard drive. Another advantage of a hard drive is you can use them as a convenient way to play music and movies through your DVD player and telly. Storing itunes on a hard disk just means you sync up through the hard drive, and is easy.

This works really well until you leave the seperate hard drive out on the patio table on a rainy night, for instance.

... when my laptop was too small to accomodate my iTunes library. At that point I kept 2 copies of the library; one on the external drive, one on a backup external drive (and technically speaking one copy on the iPod itself).

That worked OK, but as the iTunes library was on a mains-powered 3.5" HDD it was a pain having to go to one specific location (my deak) to update my iTunes. I subsequently switched to a portable 2.5" HDD, which was a LOT easier, and is the configuration I suspect that bathmat is referring to.

Since I got a larger laptop I migrated my library back onto the laptop, but keep the portable drive as a backup (sync'd regularly using Cobian backup), and more recently addded a 500GB NAS (Network Attached Storage) drive hanging off my wireless router so that my sons could access the library too - so now technically have 3 or 4 copies just in case...

Why am I so paranoid? In my professional life I'm responsible for Production and Field Quality/reliability of enterprise-class Storage products (basically big boxes of hard disks), and from experience there are two types of hard disks;

1) Those which have failed

and

2) Those which are going to fail

This colours my backup strategy a little :-)

on how big your Itunes library is and how big your laptop hard drive space is. The main thing is that you have it backed up. I fully agree with Keith above - I work for one of the disk drive companies and although they have a 5 yr warranty and the field failure rate is low, it does happen and those are no consolation when its your data.

If you have plenty of space on your laptop then leave it there and and use an external drive to back it up. Whilst an external can obviously hold more and frees up space on your laptop you have the added inconvenience of needing the extra drive - invariably one day you will pull out your laptop on the train to listen to some music and find you forgot your external drive etc.

If you are short of space, then the most convenient option is an external 2.5" drive. These are readily available in capacities at 500G (and we will be shipping 1TB external 2.5" drives by this autumn) which is sufficient for most peoples libraries. Remember though that an external drive is still a hard disk drive like the one in your laptop and can still fail - so back that up too !

Personally, I have been converting a load of DVD's for streaming around the house and so my iTunes library is pretty large. I have my iTunes library stored on a Drobo (external RAID enclosure with 4x 1.5TB drives in it that has built in data protection) connected to my IMac and then all my music and a selection of the movies on a 500G external 2.5" drive that I use with my MacBook.

As ever I appreciate the time taken to answer questions even if a bit off topic.