Allocating system resources to a virtual machine

Allocating system resources to a virtual machine

Virtual Server 2005 offers several ways to adjust a virtual machine's system resources. You can adjust how much memory is allocated to a virtual machine, and you can adjust settings that control how physical CPU resources are allocated to virtual machines.

Allocating memory

A virtual machine's memory allocation is part of a virtual machine's configuration. When you create a virtual machine, you specify an amount of memory for the virtual machine. That amount represents the maximum amount of memory that Virtual Server makes available to the virtual machine while it is running. You can modify the amount of memory when the virtual machine is turned off.

The maximum amount of memory you can assign to a virtual machine is 3.6 gigabytes (GB); however, the actual limit may be lower, depending on the available physical memory. The Memory Settings page for your virtual machine displays the range of memory that you can allocate to the virtual machine, as well as a recommended maximum. The high end of the range is based on the memory available on the physical computer. You cannot allocate more memory than what is physically available. The recommended maximum represents the highest recommended amount to use without causing performance problems.

In order to run, each virtual machine requires 32 MB of memory in addition to the amount allocated on the Memory Settings page. This includes the memory required for the emulated video RAM (VRAM) and code cache. For example, a virtual machine that is allocated 128 MB of memory actually requires 160 MB.

Allocating CPU resources

Virtual Server provides settings that you can use to control how system resources are allocated among the virtual machines that are currently running. You can allocate resources by weight and by capacity. The capacity settings give you a greater level of control than the weight setting because the capacity settings specify a minimum and maximum amount of resources to make available to the virtual machine.


Only the virtual machines for which you have permissions appear on the CPU Resource Allocation page, and only the resources allocated to them are included in the figures for Total Capacity Reserved and Available Capacity Remaining. This means that you can inadvertently over-allocate CPU resources to the virtual machines listed on this page and prevent other virtual machines from turning on. If you do not have permissions for all of the virtual machines configured on this instance of Virtual Server, we strongly recommend that you ask your Virtual Server administrator for assistance before allocating CPU resources.

The following sections summarize each setting. For more information about the settings, see Configuring CPU resources for virtual machines.

Allocating resources by weight

Using weights to allocate resources lets you to assign a number to a virtual machine that represents how important it is to provide resources to that virtual machine compared to all other virtual machines. You can assign a number from 1 through 10,000 for each virtual machine, with 1 representing the least important and 10,000 representing the most important.

Allocating resources by capacity

Using capacity settings lets you assign minimum and maximum percentages of the CPU's resources that can be consumed by the virtual machine. You can use the reserved setting to ensure that a minimum amount of resources are always available to the virtual machine. You can use the maximum setting to ensure that the virtual machine does not consume more than the specified percentage of the CPU's resources.


If there is not sufficient memory available to run a virtual machine when it is turned on, the virtual machine does not start and an error is logged to the Virtual Server event log. For more information about the event log, see Viewing and filtering Virtual Server events. The memory assigned for the virtual machine’s memory is allocated at a low level and is charged to the Virtual Server service. Because memory allocated by such a method is not charged to a process, the memory quoted by Task Manager in the host operating system for the Virtual Server service is not accurate. You can use Task Manager in the guest operating system to determine the current memory usage for a particular virtual machine.