While consolidation is a beautiful and enlightened business to occupy yourself with it can also be a tough one to beat.
On quite a few occasions i have seen technical architects and systems administrators on a mission to consolidate making a few mindslips.
1. Some technical architects tend to look at the mission on a too narrowminded basis, they think to themselves "Ah, this is so easy, we will put all systems of the same flavor on the same server, this way we will save a whole lot of resources!"
2. Some systems administrators tends to look at the mission from the wrong angle, they say out loud "Ah, nemas problemas, we will put all systems that we need to administrate on the same server, this way we will save a whole lot of time!"
3. Some CIO's tends to look at the mission from on a too stingy view, they preach to the masses "Hail me, we will put all systems running on a Windows 2008 Enterprise server on the same hardware, this way we will save a whole lot of money on license costs!"
What many people tend to forget to think about is the Service Level of Agreement, yes it may sound obvious for most of us, but this is hard facts, people do forget about the SLA.
First off you need to have it all clear to you and your management what the purpose of consolidation is. Is it, cost, workload or plain philosophy? Managing many servers isnt only expensive in license and support fees, it is also costly by the terms of man hours.
I found this very good paper on Server consolidation over at DataCentres.com, see http://www.datacentres.com/papers/papers/serverconsol.pdf
