I have a client that is looking to upgrade his site as well as his hosting package. The site receives a huge amount of traffic (300 GB mth - 400,000 unique monthly visitors). The new site will also need to use a database. Windows platform. Would a high end dedicated server package with the site and database on the same machine work? Or would the site need multiple servers?

Also, another client that also has a database driven website would like to upgrade their set up. They receive in the amount of 10-15,000 unique monthly visitors (not sure exactly about the bandwidth - but it should be pretty consistent as the above example - in the range of 12-20 GB monthly of transfer. What type of set up would be suitable for this type of site? There is no streaming video or audio on either site if that matters.

Any advice would be greatly appreciated.

I once had a person describe dedicated vs. shared this way (and it has stuck with me) :

Think of your hosting as your apartment. If you want to be in a shared envrionement (have roommates), expect that you have the ability to be affected by other people. Other people's mess can effect you. But for that, you will pay less. If you want dedicated (or live by yourself), you will pay more but you don't have to deal with other people and you can walk around in your underwear without worrying about it

Thanks for you post. I understand the difference between shared hosting and a dedicated server. I was wondering if I could get by with one server, or would I have to start considering load balancing on a cluster and would therefore need multiple server machines.

depending on the budget of your client, starting with one is probably fine. A well confiured, solid server can handle both web and database pretty easily and give you quite a bit and give you room to grow. If you later find out that one server is not enough, you can always add more.

No sense in your client spending more than you need when you are unsure.

I would do some benchmarking and find out about the CPU / mem utilization before making a decision on the server and on hosting 2 database driven websites on the same server. The problem in your case will defenetly won't be the bandwidth because most of the hosting companies nowdays offer more than 500GB of bandwidth for their dedicated boxes. Do some research, optimize the application and the database before wasting your time and money.

So I'm probably alright hosting each one of these sites on their own dedicated server, I just have to monitor the performance of the machine (bandwidth I'll be OK - just want to make sure the site won't be under serious strain).

If you have the budget and the ability to manage the 2 servers - definetly go with different boxes

You mean each site with it's own dedicated server, or the big site with two servers, and the smaller site with one?

The best you can do is to have 2 servers in a cluster where one of the servers is hosting the first site, the other one the 2nd. You can also perform data syncronization and database replication between the servers to achieve maximum uptime. If the big site needs better server you can either get better server or start looking into load balancing.

300GB per month data transfer is not small potatoes. No matter what dedicated packages companies are offering these days, this amount of traffic should be taken seriously.

One dedicated box might suit this web site initially, but site's like this are destined to grow. Also, I suppose you probably know best what features this site has that would be resource-intensive - forums? custom scripts? shopping carts? Not only is controlling server load important to keep it up and running, but to provide the site's visitors with a pleasant optimized experience as they use the site. Getting multiple dedicated servers to serve a web site of this nature is not uncommon, in fact, it provides redunancy/backup.

Best of luck with the setup. It can be exciting handling large accounts like this and watching them grow.

Setting up a cluster with fail over and load balancing is not as easy as getting bunch of dedicated servers..