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Calculating the priority level of a VMware DRS migration recommendation (1007485)

Details

VMware DRS assigns integer priority ratings to the migration recommendations it makes. You can better understand the meaning of a priority rating if you are aware of the algorithm that calculates it.

Solution

For each migration recommendation, the priority level is limited to the integer range priority 2 to priority 5 (inclusive). It is calculated according to this formula:

6 - ceiling(LoadImbalanceMetric / 0.1 * sqrt(NumberOfHostsInCluster))

Here, ceiling (x) is the smallest integer value not less than x. LoadImbalanceMetric is the current host load standard deviation shown on the cluster's Summary page of the vSphere Client.

For each host:

Compute the load on the host as

sum(expected VM loads) / (capacity of host)

This value is the host load metric.
Compute the standard deviation of the host load metric across all hosts to determine LoadImbalanceMetric.

These formulas apply only to ESX/ESXi 4.x and VCenter Server 4.x. They are subject to change.

Keywords

DRS, migration recommendation, priority level, algorithm

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