I need advise about setting up a server plan for a community.

Question

I have the following situation:
The website has a community with, expected in the fist stage, 100,000 registered members. This community will be first launched in the Netherlands and later worldwide. A member has 25 MB of disk space to store photos or something. You can compare the community with for example hyves (a dutch community site similar to MySpace)
Besides the community the site will also have a web shop and some information pages about the products that will be sold in the shop. The web shop will not have a large amount of product in store, however the expectation is that it will attract a large amount of customers.
My question is; what do I need to keep this running smooth (quick page loads) and secure (data loss, back-up servers), and make it easy to expand the server park.
URLs to the example sites:
Hyves: www.hyves.nl
MySpace: www.myspace.com

Answer 1

>Can you clarify that, because I thought the Xserve RAID is the server for storage?
The XServe RAID is not a 'server for storage'. It's just an array. In order to provide storage it needs to be connected, via Fiber Channel to a host computer. This is fine if you have one web server, but becomes tricky when you have multiple. unless you're doing some very fancy load balancing, you're likely to want all the content accessible to all web servers at the same time. To do that you typically implement a fiber channel SAN (every host connects to the XServe RAID via a fiber channel connection), or you implement a NAS host where one server is attached to the XServe RAID and it shares the content to other hosts via AFP, NFS or similar.
This is fine for small installations but my point is that if you grow to hundreds of terabytes of storage, the XServe RAID might not be the best bet. It works well enough at tens of terabytes but there are other considerations when you get very large.
For example, if you have one XServe host acting as an AFP or NFS 'head', what happens to your site when that server crashes? or needs a Software Update? Your network is going to go down. For high availability networks you might consider a dedicated NAS or SAN infrastructure that has higher redundancy, built-in failover and is designed for very large storage arrays. If you expect to grow there you might be better off starting off with that, rather than starting with an XServe RAID and migrating the data later on.
Other than that, the rest of it is good for a start, but you need to consider redundancy (what do you do if a server crashes?) and scale (what do you do when you get more traffic than your web server can handle?).
Typically these problems are solved via load balancers - appliances that sit in front of the application server and dynamically routes connections to whaever machine is best able to respond to the request. These boxes (at least the good ones) don't come cheap, but they're essential if you expect your site to grow past a single server setup.