Hello,
here is my question:

1- I would like to know if you want to get a server do you get it 1U or more "2U, 3U..." and why do you choose this size of cases?

2- which one do you think its better to host 400 accounts on 4 1Us server, or to host 400 account on one 4U server?

Thanks for your help.

100 accounts on 4 servers. Distributes the risk that you'll piss of all 400 accounts when your servers fries, but it increases the risk that one of servers will fry simply because you have a greater number of servers. The first case is more important than the second case. Besides, your customers will be happier with more breathing room.

George

I couldn't of said it better myself.

And besides, if you've got 4x 1U 2xP3 2GB 2x18GB machines with 500 very happy clients on them versus 1x 6U 4xP3X 8GB 5x36GB machine, you're going to have a lower equipment cost too.

George