Setting Memory Limits for All Virtual Machines

Select: Edit > Application Settings > Memory

VMware GSX Server assigns memory to virtual machines in the following way:

A specific amount of memory, called reserved memory, is set aside from the total pool available on the physical machine.
Each virtual machine is configured to use a certain amount of the reserved memory.

In addition, when you power on a virtual machine, VMware GSX Server checks to be sure there is enough memory available to run that virtual machine.

Memory Limits (Checks)

By default, a virtual machine checks to ensure that enough free memory is left for the host machine to continue to operate efficiently:

First, it performs a check when it powers on to ensure that the total amount of memory allocated to all running virtual machines does not exceed the total physical memory of the host.
Second, the virtual machine periodically checks that the reserved memory allocated to currently running virtual machines does not exceed the total amount of reserved memory.

If these checks fail, the virtual machine does not power on.

You can disable memory checks by deselecting Enable memory limits, but remember that disabling these checks can result in poor performance and even system crashes if you try to run a virtual machine with too much or too little memory for your host system.

Reserved Memory

To provide good overall system performance, VMware GSX Server limits how many virtual machines can run at once based on the amount of available reserved memory. In doing so, VMware GSX Server prevents virtual machines from causing each other to perform poorly.

The default amount of reserved memory is calculated when you install VMware GSX Server, but you can change the amount of reserved memory using the Reserved size setting in this panel.

Warning: Changing the amount of reserved memory is recommended only for advanced users because it can have an adverse impact on the host or virtual machine performance.

Reserving too much physical memory can cause the host to thrash, or even hang, if other applications are competing for memory on the host.

Reserving too little physical memory can cause virtual machines to perform very poorly and also limit the number of virtual machines that can be run. This happens because if free memory falls below a minimum value (specific to each host), the host operating system continually frees up memory by swapping to disk to maintain that amount of free memory. This pattern causes the virtual machine to run slowly as well.

After making any changes in this panel, click OK to save the changes and close the Preferences dialog box.