Right, so I know RAID set ups are to do with how multiple hard drives work with each other in a storage capacity, but which is which?

At the mo I have a single NAS drive with a 400gb drive in it. This is getting filled up quicker than I thought it would. I could open it up and stick a 750gb drive in, but after that, drives get pretty damn expensive!!!!

So would it be work going for a NAS box that does RAID configs, and running multiple discs?

If so, what config? I know you can have mirror discs - so if you have 2x 500gb drives and set them to mirror you still only have 500gb of storage, but you have a live backup of that 500gb drive in the other 500gb drive - what RAID is this?

Next, If I have a NAS box with 4 500gb drives, how could I get the PC's connected to it (via network) to see it as a total capacity of 2tb? Which RAID config would this be?

Cos the problem with my NAS box is that whilt I can connect an external drive to it (either USB2 or eSATA) it is a seperate drive and not shown as a continuation of the NAS box, as in total storage capacity....