DRS evaluates potential memory load balancing migrations based on a metric derived from the ESX active memory estimate in addition to a percentage of idle consumed memory, which is 25 percent by default. DPM uses this memory demand metric to compute host memory utilization as the sum of the memory demand made by virtual machines on a host divided by that host's memory capacity for running virtual machines. In environments where memory over-commitment is completely avoided, for example where the memory size of all virtual machines is kept fully backed by physical memory, the DRS memory demand metric is too low.

In version vCenter Server 5.1 Update 2c and later and in all the versions of vCenter Server 5.5, the memory demand metric used by DRS and DPM can be modified to include a configurable percentage of idle consumed memory by modifying the DRS advanced option PercentIdleMBInMemDemand. In environments where the memory size of all virtual machines is fully backed by physical memory, setting the value to 100 percent is appropriate.

In vSphere versions earlier than vSphere 5.5, several workarounds to these DRS and DPM behaviors exist.

• Lower DRS aggressiveness to reduce undesirable DRS load-balancing moves. You can use the existing DRS advanced option IdleTax to increase the idle memory included in the load balancing metric.

• Lower DPM aggressiveness to reduce excessive DPM consolidation of memory. You can reduce DPM's target utilization by using the DRS advanced option DemandCapacityRatioTarget.

For information on configuration see KB 2059354