Understanding the Issue
The administrator is investigating VM performance complaints and is analyzing CPU Ready Time data.
* CPU Ready Time is a crucial metric in Nutanix and virtualization environments (AHV, ESXi, or Hyper- V).
* It measures the amount of time a VM is waiting for CPU scheduling due to resource contention.
* High CPU Ready Time indicates that VMs are ready to run but are waiting because the host lacks available CPU resources.
Analysis of the Exhibit
* The graph shows CPU Ready Time spikes for multiple VMs.
* Some VMs have CPU Ready Time exceeding 18% to 21.5%, which is very high.
* A healthy CPU Ready Time should be below 5%.
* Values above 10% indicate CPU contention, and anything above 20% is critical and requires immediate troubleshooting.
Evaluating the Answer Choices
#(A) Check the number of vCPUs assigned to each CVM. (Incorrect)
* CVMs (Controller VMs) have fixed CPU allocation, and modifying their vCPU count is not recommended unless advised by Nutanix Support.
* The issue is related to VM CPU contention, not CVM configuration.
#(B) Review host CPU utilization. (Correct Answer)
* High CPU Ready Time suggests CPU overcommitment or host saturation.
* The administrator should check host CPU usage in Prism Central to determine if the cluster is overloaded.
* If host CPU usage is consistently above 85-90%, VMs are competing for CPU resources, leading to high CPU Ready Time.
#(C) Assess cluster SSD capacity. (Incorrect)
* SSD capacity impacts storage performance (latency, read/write speeds) but does not affect CPU Ready Time.
* High CPU Ready Time is a CPU scheduling issue, not a storage bottleneck.
#(D) Enable VM memory oversubscription. (Incorrect)
* Memory oversubscription does not impact CPU scheduling.
* Enabling memory oversubscription affects RAM allocation, but CPU Ready Time is strictly related to CPU contention.
Next Steps to Diagnose & Resolve the Issue
* Review Host CPU Utilization:
* Navigate to Prism Central # Analysis # CPU Usage per Host.
* Identify hosts experiencing high CPU load.
* Check VM vCPU Allocation:
* Ensure that VMs do not have excessive vCPUs assigned, which can lead to scheduling inefficiencies.
* Overprovisioning vCPUs can cause unnecessary contention.
* Balance Workload Across Hosts:
* Use Nutanix AHV DRS (Dynamic Scheduling) or VMware DRS to redistribute VMs across hosts.
* Check if certain hosts are overloaded while others have spare CPU capacity.
* Consider Scaling Out the Cluster:
* If CPU usage is consistently high, adding more nodes may be required to reduce CPU contention.
Multicloud Infrastructure References & Best Practices
* CPU Ready Time Best Practices:
* Keep CPU Ready Time below 5%.
* Avoid overcommitting vCPUs on heavily loaded hosts.
* Monitor Prism Central Runway Metrics to predict future CPU resource needs.
* Nutanix AHV CPU Scheduling Optimization:
* Ensure proper VM sizing (avoid excessive vCPU allocation).
* Balance workloads using Nutanix AHV DRS.
References:
Nutanix Prism Central: Performance Analysis and CPU Metrics
Nutanix Bible: VM Performance and Resource Management
Nutanix KB: Troubleshooting High CPU Ready Time in AHV