Memory Overcommitment in the ESX Server

Virtualization of computer hardware continues to reduce the cost of operation in datacenters. It enables users to consolidate virtual hardware on a smaller number of physical hardware, thereby efficiently using hardware resources. The consolidation ratio is a measure of the virtual hardware that has been placed on physical hardware. A higher consolidation ratio typically indicates greater efficiency. VMware’s ESX R © Server is a hypervisor that enables competitive memory and CPU consolidation ratios. ESX allows users to power on virtual machines (VMs) with a total configured memory that exceeds the memory available on the physical machine. This is called memory overcommitment. Memory overcommitment raises the consolidation ratio, increases operational efficiency and lowers total cost of operating virtual machines. Memory overcommitment in ESX is reliable. It does not cause VMs to be suspended or terminated under any conditions. This article describes memory overcommitment in ESX, analyzes the cost of various memory reclamation techniques and empirically demonstrates that memory overcommitment induces acceptable performance penalty in workloads. Finally, best practices for implementing memory overcommitment are provided. General Terms memory management, memory overcommitment, memory reclamation