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When you use the failover level policy, vSphere HA partitions resources into slots. A slot represents the minimum CPU and memory resources that are required to support any powered-on virtual machine in the cluster.
With the failover level policy in place, HA uses the following slot calculations to control virtual machine migration within the cluster:
If your cluster contains any virtual machines that have much larger reservations than the others, they will distort slot size calculation. To avoid this, you can specify an upper bound for slot sizes; use the configuration editor in the vSphere Client to set the das.slotCpuInMHz and das.slotMemInMB attributes. When you use these attributes, there is a risk that resource fragmentation will cause virtual machines with resource requirements larger than the slot size to be assigned multiple slots. In a cluster that is close to capacity, there might be enough slots in aggregate for HA to successfully failover a virtual machine. However, if those slots are located on multiple hosts, a virtual machine assigned multiple slots cannot use them because a virtual machine can run on only a single host at a time.
The CPU slot resource is the host CPU resource amount divided by the CPU component of the slot size; the result is rounded down. HA makes the same calculation for host memory resource amount. HA compares the results; the lower of the two numbers is the host slot capacity.
Properties
Name | Type | Description |
---|---|---|
failoverLevel | xsd:int |
Number of host failures that should be tolerated, still guaranteeing
sufficient resources to restart virtual machines on available hosts.
|
slotPolicy* | ClusterSlotPolicy |
A policy for how to compute the slot size. If left unset, the slot is
computed using the maximum reservations and memory overhead of any
powered on virtual machine in the cluster.
Since vSphere API 5.1 |
Properties inherited from ClusterDasAdmissionControlPolicy | ||
resourceReductionToToleratePercent | ||
Properties inherited from DynamicData | ||
None |
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