Host CPU overutilization may impact vSAN performance

Products

• VMware vSAN

Issue/Introduction

CPU Ready values can be monitored via vSAN Performance Dashboard in vRealize/Aria Operations Manager. Temporary or sustained increase of that metric seen on one (or more vSAN hosts) may manifest in increased READ/WRITE latencies for Virtual Machines.

Environment

VMware vSAN 8.x

Cause

In a vSAN environment, CPU Ready should be ideally near 0% and below 1%. When vSAN modules are forced to wait for CPU (Ready state), storage latency is the direct result.

Resolution

vSAN modules run in ESXi kernel. Presence of CPU ready values over 1% (or between 0% and below 1% if sustained) does indicate heavy CPU oversubscription and can be caused by:

• High Consolidation Ratio
• Over-allocation (Oversizing)
• Noisy Neighbor VMs

Consider workload (Virtual Machine) rebalancing and review/adjust of workload characteristics (achievable vCPU allocation ratios/usage patterns) to decrease vSAN CPU Ready values. 

 

Additional Information

Additional Information: 

https://techdocs.broadcom.com/us/en/vmware-cis/aria/aria-operations/8-16/vmware-aria-operations-configuration-guide-8-16/predefined-dashboards-in-vrealize-operations-manager/performance-dashboards/vsan-performance-dashboard.html