Minimum number of server for Clustering

[Mark Arnold]

Hi,

I tried searching the old threads, but the search came up with too many results that all seemed unrelated...

I am wondering how many server I need for a reasonable cluster setup. I realise this depends highly on the scenario, but is it reasonable at all to work with only two machines as long as the performance is ok? How would they be set up then?
I am mainly trying to get some redundancy in for now...

Also, does it make sense to have a cluster consisting out of a bunch of machines that are split up into to locations and connected over a cipe tunnel (lowfish encryption) through the internet? Or is this kind of setup usually to unreliable and the connection too slow?

Thanks,

MARK