VMs - Load Balancing

Question

Hello.After update to AHV 11.0.1.6, AOS 7.5.1.10 the behaviour of our cluster changes.Before the update, the machines were distributed evenly across all hosts at startup.Now the clients started on small number of hosts. When the host reaches 90% CPU-Util, the next host will be used.On our hosts we have nVidia A16 installed. With 60VMs on one host (were using 2Q and 4Q profiles) the VMs don’t work as expected anymore.Nutanix support means, that this behaviour is normal.. I don’t think so.Is there a chance to achieve a better distribution of the VMs?With the actual situation a normal work is for our users not possible. Thanks in advance for your answers. RegardsDirk Emmermacher

DrewPlaster · Answer

Acropolis Dynamic Scheduling (ADS) is responsible for the initial placement of VMs and runtime optimization. When multiple hosts are available, ADS should select the host with the overall highest availability (CPU, memory, storage-controller, and vGPU). The 90% CPU utilization threshold you mentioned is close to ADS 85% threshold. ADS specifically monitors host CPU usage and triggers migration tasks to resolve contention only if resource utilization remains greater than 85% for a 10-minute span.

Here are some things to investigate that may be causing abnormal ADS behaviour:
1) Verify ADS is Enabled
ADS should be enabled by default but something/someone may have disabled it although if you're getting VM relocations at 90% it is more than likely enabled.
2) Check for VM-VM Anti-Affinity Policies
During initial startup placement ADS soft enforces these policies; it will prefer to start the VM on a separate host but will prioritize starting the VM over non-compliance if resources are constrained. At runtime to resolve contention, ADS will reject a migration if it results in a violation of a VM-VM anti-affinity policy.
3) Monitor and Resolve Dynamic Scheduling Failures
If the cluster is imbalanced but VMs are not migrating, check for ClusterHotspotAvoidanceNotPossible alert in Prism. This occurs if ADS cannot build a plan to resolve contention and could be due to insufficient CPU or CVM resources, affinity policy constraints that prevent migration targets, the presence of non-migratable VMs (VMs with GPU/CPU pass-through or vNUMA configured)

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