Actually, DRS will sometimes move VMs around to balance load even if all VMs are getting the resources they need or are entitled to. It depends partly on how high you set the aggressiveness rating. If you set it to most aggressive, DRS tries to keep load very balanced, and so you'll see more VMotions at this setting than at the lower settings - if your load changes at all. Here's a list of some of the criteria that DRS uses to assess whether to recommend a VMotion or not:
a) Is the VM getting the amount of resources it is entitled to? (In the case of very light load, the answer to this is always yes)
b) degree of load imbalance relative to the aggressiveness setting you've configured
c) sum of VM reservations on a host < total capacity of the host
d) ping-pong prevention: looks at historical load information to avoid constantly moving around VMs whose load keeps changing
Ulana
