Administration Guide › Managing Virtual Environments › VMware vSphere and vCenter Server › Resource Allocation › Resource Allocation Reservation

Resource Allocation Reservation

A reservation specifies the guaranteed minimum CPU or memory allocation for a virtual machine, resource pool, or vApp. vSphere allows you to power on a virtual machine only if there are enough unreserved resources available for the virtual machine. The server guarantees that amount of reserved resources even when the physical server is heavily loaded. The reservation is defined in megahertz or megabytes.

For example, assume you have 2GHz CPU available. Then specify a reservation of 1000 MHz for VM1 and 1000 MHz for VM2. Now each virtual machine is guaranteed to get 1GHz if necessary. However, if VM1 is using only 500MHz, VM2 can use 1.5GHz.

The reservation default is 0. You can specify a reservation to guarantee that the minimum required amounts of CPU or memory are always available for the virtual machine.