VMware vSphere 4 Technical Information download pdf (Page 40)

Performance Best Practices for VMware vSphere 4.0

40 VMware, Inc.

VMware Distributed Power Management (DPM) Best Practices

Distributed Power Management (DPM) conserves power by migrating virtual machines to fewer hosts when

utilizations are low. DPM is most appropriate for clusters in which composite virtual machine demand varies

greatly over time; for example, clusters in which overall demand is higher during the day and significantly

lower at night. If demand is consistently high relative to overall cluster capacity DPM will have little

opportunity to put hosts into standby mode to save power.

Most DRS best practices (described in “VMware Distributed Resource Scheduler (DRS) Best Practices” on

page 38) are relevant to DPM as well.

 The more hosts in the cluster, the more opportunity there is for power savings through DPM. However

don’t exceed the maximum allowed in the Configuration Maximums for VMware vSphere 4, listed in

“Related Publications” on page 8.

 DPM can only be enabled on hosts running ESX 3.5 or later. (Note that DPM is supported between

hosts running EX 3.5 and ESX 4.0, subject to the VMotion limitations detailed in “VMware VMotion

and Storage VMotion” on page 37.)

 Having VMotion-compatible hosts in the cluster is important, since DPM needs to be able to migrate

running virtual machines onto fewer hosts to be able to put some hosts into standby mode to save

power.

 Similarly, having wake-on-LAN (WOL) capable hosts in the cluster is beneficial. The ability of DPM

to place a host in standby and power it on again later depends on ESX host software and on the

network interface having hardware support for wake-on-lan. The more of the hosts in the cluster

support DPM standby/power-on operations the more choices DPM has for saving power.

 Enabling DPM with all hosts in the cluster being in automatic mode gives DPM the most flexibility in

choosing hosts for power down/up. For hosts in manual DPM mode, DPM must query the user about

power down/up of the host. For this reason, DPM prefers choosing hosts in automatic mode over those in

manual mode. If desired, DPM can be disabled for specific hosts.

 DPM considers historical demand in determining how much capacity to keep powered on and keeps

some excess capacity available for changes in demand. DRS will also power on additional hosts when

needed for unexpected increases in the demand of existing virtual machines or to allow virtual machine

admission.

 In a cluster with VMware High Availability (HA) enabled, DRS/DPM maintains excess powered-on

capacity to meet the High Availability settings. The cluster may therefore not allow additional virtual

machines to be powered on and/or some hosts may not be powered down even though the cluster may

appear to be sufficiently idle. These factors should be considered when configuring HA.

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VMware vSphere 4 Technical Information Page 40