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Manually configuring HA slot sizes in vSphere 5.x (2033248)

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Automatic slot size calculations appear larger than is needed.


The admission control policy that configures the number of host failures a cluster tolerates uses slot sizes as a generalized representation of a virtual machine in the environment. In vSphere 5.0 and newer, a slot size is set at the highest reservation of memory or CPU. If there are no reservations, CPU is set at 32 MHz and memory is 0MB + Overhead (as defined in the Resource Management Guide). For more information, see the VMware vSphere Availability guide.
This article provides steps to manually configure HA slot sizes in vSphere 5.1.


In vSphere 5.0 and earlier, configuring the slot size was done using cluster advanced configuration options of das.slotCpuInMHz and das.slotMeminMB.

Note: This sets the upper bound that the slot can be, but it does not set the actual value. If reservations are lowered, the slot size is also lowered below this configured value.

In vSphere 5.1, you can set these values in the cluster settings in the vSphere Web Client, under Slot Size policy and Fixed slot size

Note: Configuration this way sets the exact value.

To set the slot size:

  1. In the vSphere Web Client, browse to the vSphere HA cluster.
  2. Click the Manage tab and click Settings.
  3. Under Settings, select HA and click Edit.
  4. Expand Admission Control to display the configuration options.
  5. Select the admission control policy to apply to the cluster.
  6. Click OK.

    Admission control is enabled and the policy chosen takes effect.

See Also

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