DRS migrates VMs when the cluster appears/shows balanced after upgrading to vCenter Server 6.0 U3 or 6.5

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:

• DRS performs too many migrations after upgrading to vCenter Server 6.0 U3 or later versions.
• DRS cluster appears/shows balanced.

Environment

VMware vCenter Server Appliance 6.0.x
VMware vCenter Server 6.0.x
VMware vCenter Server Appliance 6.5.x
VMware vCenter Server 6.5.x

Cause

Starting from vSphere 6.0 U3 and 6.5, if it detects a pairwise imbalance between two hosts, DRS will continue load balancing after the standard deviation based load balancing is complete. A pairwise imbalance exists when the resource usage of any two hosts differ by more than a threshold (default = 20%).

 

This could result in VM migrations even when the cluster appears balanced according to standard deviation.

 

Resolution

This issue is resolved in vCenter Server 6.0 U3j available at VMware Downloads.
This issue is resolved in vCenter Server 6.5 U2d available at VMware Downloads. 

Workaround:

If you are unable to update to a release in which the issue is resolved, as a workaround you can switch back to the old behavior by turning off the Pair-wise balancing by setting the cluster advanced option CheckPairwiseImbalance to 0.

Note: Advanced option "CheckPairwiseImbalance" is case sensitive.

This will disable this enhancement and revert to the same behavior as before.

Additional Information

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升级到 vCenter Server 6.0 U3 或 6.5 后，DRS 在群集显示平衡时迁移虚拟机