I realise a Storage Area Network allows many servers to access different storage devices over a network. However this means that say a database server can access the files of a web server? Also as there will be different physical storage devices, does each 'server' have its own storage device on the other end of the network? Thanks

Depends on the place you go for define. Each server doesn't really need it's own storage. It may boot off the network or have a small drive just for the OS. To be part of the network (storage network) it could or may not need access to that resource. I read it wrong and answer it wrong too. So get off my case you peanut.

However this means that say a database server can access the files of a web server? The point of the SAN would be to have your db server running from one server (with it's own OS of course, that goes without saying), but all data relating to the db stored on the SAN. The SAN centralizes storage and therefore backup as well. If one server needs to access the data of another server, it would do so via the SAN as your SAN would be the central storage for all servers in your environment. I'm not sure you'd want your web servers storing data in the SAN as the SAN would be inside the local zone and the web server(s) outside of it in the DMZ. I'm sure it could be done, but would be tricky because of the involved routing and firewall(s). But for all internal servers, yes, you would want them storing their data on the SAN.