VMware ESX Server 2.0Features | Documentation | Knowledge Base | Discussion ForumsThese guidelines are intended to help system administrators determine an appropriate amount of hardware memory for running a virtual machine workload on ESX Server 2.0. Since the characteristics of your particular workload also influence memory needs, you should follow up with testing to confirm that memory sizes computed according to these guidelines achieve the desired results. ESX Server uses a small amount of memory for its own virtualization layer, additional memory for the service console and all remaining memory for running virtual machines. The sections below explain each of these uses and provide a quantitative sizing example. ESX Server 2.0 uses approximately 24MB of system memory for its own virtualization layer. This memory is allocated automatically when the ESX Server is loaded and is not configurable. The recommended amount of memory to configure for the service console varies between 192MB and 512MB, depending on the number of virtual machines you plan to run concurrently on the server:
The remaining pool of system memory is used for running virtual machines. ESX Server manages the allocation of this memory to virtual machines automatically based on administrative parameters and system load. ESX Server also attempts to keep some memory free at all times in order to handle dynamic allocation requests efficiently. ESX Server sets this level at approximately 6 percent of the memory available for running virtual machines. Each virtual machine consumes memory based on its configured size, plus additional overhead memory for virtualization. The dynamic memory allocation for a virtual machine is bounded by its minimum and maximum size parameters. The maximum size is the amount of memory configured for use by the guest operating system running in the virtual machine. By default, virtual machines operate at their maximum allocation, unless memory is overcommitted. The minimum size is a guaranteed lower bound on the amount of memory that is allocated to the virtual machine, even when memory is overcommitted. The minimum size should be set to a level that ensures the virtual machine has sufficient memory to run efficiently, without excessive paging. The maximum size can be set to a higher level to allow the virtual machine to take advantage of excess memory, when available. Overhead memory includes space reserved for the virtual machine frame buffer and various virtualization data structures. A virtual machine configured with less than 512MB of memory requires 54MB of overhead memory for a single virtual CPU virtual machine, and 64 MB for a dual-virtual CPU SMP virtual machine. Larger virtual machines require an additional 32MB of overhead memory per additional gigabyte of configured main memory. For example, a single virtual CPU virtual machine with a configured maximum memory size of 2GB requires 102MB of overhead memory. |
