VMware GSX Server 2.5.2Features | Documentation | Knowledge Base | Discussion Forums The second configuration parameter that users can set is the amount of memory that GSX Server is allowed to reserve for all running virtual machines. This parameter can be set in Settings > Preferences > Memory (on Windows hosts) or Settings > Reserved Memory (on Linux hosts). This setting specifies a maximum amount that GSX Server is allowed to reserve. But this memory is not allocated in advance. Even if multiple virtual machines are running at the same time, however, GSX Server may be using only a fraction of the reserved memory. Any unused reserved memory is available to be used by other applications. If all the reserved memory is in use by one or more virtual machines, the host operating system cannot use this memory itself or allow other applications to use it. The memory used by GSX Server includes the memory made available to the guest operating systems plus a small amount of overhead memory associated with running a virtual machine. The amount of overhead memory required depends upon the size of the guest's virtual disks, its behavior and the amount of memory allocated to the virtual machine. Refer to the table below for the typical upper limit needed, based on the amount of memory allocated to the guest.
The amount of memory actually used for a particular virtual machine varies dynamically as a virtual machine runs. If multiple virtual machines run simultaneously, they work together to manage the reserved memory. The recommended amount of memory to reserve for all running virtual machines is calculated on the basis of the host computer's physical memory and is displayed in the reserved memory settings control — Settings > Preferences > Memory (on Windows hosts) or Settings > Reserved Memory (on Linux hosts). If you determine you want GSX Server to reserve more or less physical memory, you can use this control to change the amount. Reserving too much physical memory can cause the host to thrash, or even hang, if other applications are run 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. By default, GSX Server limits the number of virtual machines that can run at once based on the amount of reserved memory. This prevents virtual machines from causing each other to perform very poorly. If you try to power on a virtual machine when there is insufficient reserved memory available, it fails to power on. You can change the memory check so it only displays a warning message, rather than preventing the virtual machine from powering on. To do so, go to Settings > Preferences > Memory (on Windows hosts) or Settings > Reserved Memory (on Linux hosts) and clear the Enable Memory Limits check box. By default, virtual machines perform checks to ensure that the amount of memory allocated to running virtual machines plus an overhead does not exceed the limits imposed by the user or by GSX Server defaults. If you need to allocate more memory to your virtual machines, you can disable the memory checks (also called memory limits) and change the memory limits. When you disable the memory checks, you:
Caution: Disabling the memory limits check can result in poor performance for both the host operating system and guest operating systems. Disabling memory checks can also result in system crashes, low memory warnings or processes in the host abnormally terminating. To disable memory checks, complete the following steps.
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