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Our company is getting ready to upgrade our infrastructure by moving away from physical machines, and into load balanced VMs. We are trying to decide how many VMs we need, and I am curious how others separate their servers. We will be running Exchange,AD,SQL,IIS,Print Server, and alot of internal license services all on 2008 R2 OS's.
Should we put each service on its own VM, or keep some of them together if the overhead is low(such as AD). What are large companies doing in regards to this? I looked for some best practice docs but couldn't find anything useful outside of SQL.