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Systems & Data Center · Intermediate

Virtual CPU (vCPU)

A virtual processor presented to a VM, scheduled by the hypervisor onto physical cores or threads.

Definition

Overcommitting vCPUs relative to physical cores is common, but excessive vCPU counts can raise scheduling wait (CPU ready). Right-sizing VMs with only the vCPUs they need often improves performance.

Example

A host with 32 physical cores runs VMs totaling 96 vCPUs at a 3:1 ratio.

Exam tip

Adding vCPUs to a VM with high CPU ready time can make performance worse.

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