What and when to virtualise a service or application is not a simple answer and will depend as much on the environment it is being used in as the service itself.
A good example of this is SQL which VMware have advised on being virtualised for a number of years and although Microsoft supports SQL in a virtual environment they are considerably more caution when it comes to actually recommending it be virtualised.
The table below gives some advice on what should be virtualised on your journey through virtualisation on the way to the "Cloud".
|Ease of Virtualisation|
|Easy||Will require additional work||Stay Physical for now at least|
|DHCP||SQL (2)||Backup Media servers|
|Active Directory Domain server (1)||Servers in DMZ (5)||Servers with dongles|
|Management server ( e.g. System Centre)||Legacy App servers||Dynamics|
|Monitoring servers||IBM software Applications (4)|
|Cisco management servers||Any servers not running X86 chipset will require specialist hypervisor|
|Web Servers||Video streaming|
|File and print services|
NB This list is by no means exhaustive and individual requirements maybe different
1. Active Directory servers can and should be virtualised, with the caveat of leaving one physical or at a minimum two DC's on different hosts. Microsoft Hyper-V actually provides a method of cloning DC's
2. SQL Will depend on size and profile of databases
3. Oracle can cost more unless virtualised on Oracle VM
4. IBM. A number of IBM back office products have a licensing model tied to physical CPU's and may be cost prohibitive when moving to a virtual environment
5. DMZ servers can be placed on hosts that also reside in the core network but use separate physical network connection. More of a concern is certain security models and certifications require total physical separation meaning dedicated hosts may be required in the DMZ.