As someone who has spent the last 5+ years specifying and building servers, the shift to a virtual environment has been... interesting. From the moment I first heard about SAN technologies and, later, virtualisation, it's made a lot of sense. However, it's only in the last month or so, when taking a step back and thinking things through has the true potential hit me.
(Apologies to those who are quicker than I am; I'm sure this will cause a few people to go "duh!").
Previously, when asked to specify a server, a number of metrics would be considered: Processor load, memory requirements, disk usage and performance. These would be totted up and a server specified. The result is a server room with a large number of servers, most of them 1U, sitting idle for the majority of the time while waiting to run a single service. Of course, when it came to adding more disk, this was often a problem as the previously specified server is now full (typically a 1U server would be specified as more would be overkill... until the upgrade is required).
The implementation of a SAN therefore made a lot of sense. By consolidating all storage into a central location, disks can be added and distributed as necessary. The first use of the SAN was quite reactive and basically involved assigning a bunch of disk to a box for file serving. The second server to use the SAN basically took so much disk (24x73GB FC disks) that the effect was the same as adding the arrays directly. The next step however will be more intelligent - to effectively utilise a SAN, I think you need to provision the storage up front so that you can proactively assign it when needed.
The same applies I think to virtualisation. I've spent a couple of weeks now working on the detail of a new server room infrastructure that is virtual. Getting my head around the idea that I no longer need to be specifying specific servers, but rather capacity, has taken some mental adjustment. The result is a breakdown of a server into components that units can purchase, starting with a basic server (1xCPU, 512MB RAM, 1x36GB disk) and then scaling up as necessary.
So today, I plan to take a close look at specifying a couple of servers that are meaty enough to host a number of virtual machines. I was originally looking at the Sun Fire X4100 - a 1U server capable of supporting 2 x dual core Opteron processors. Having spent a bit of time getting to grips with the possibility of creating a large number of servers as necessary, the X4600 (capable of 8 x dual core Opterons) seems more appealing, as additional capacity can be bought at a later date.
All exciting stuff...