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Systems & Data Center · Intermediate

Memory Overcommitment

Allocating more total memory to VMs than the physical host has, relying on reclamation techniques when demand peaks.

Definition

Hypervisors reclaim memory through transparent page sharing, ballooning, compression and, as a last resort, hypervisor swapping. Overcommitment improves density but can degrade performance under pressure.

Example

A 512 GB host runs VMs configured with 700 GB total memory because most VMs use far less.

Exam tip

Hypervisor swapping is the worst-performing reclamation technique; ballooning is preferred.

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