VMware GSX 3 - Manual (Page 195)

C H A P T E R 6 Performance Tuning and the VMware GSX Server Host
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Specifying How Much RAM is Used by All Running
Virtual Machines
You can set the amount of host RAM that GSX Server is allowed to reserve for all
running virtual machines. To set this parameter, choose Host > Settings > Memory.
The reserved memory setting specifies a maximum amount of host RAM that GSX
Server is allowed to use. But this memory is not allocated in advance. Even if multiple
virtual machines are running at the same time, GSX Server may be using only a
fraction of the RAM you specified here. Any unused RAM is available for use by other
applications. If all the RAM you specify here 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.
Virtual Machine Overhead
Virtual machines require relatively large amounts of memory to operate with
reasonable performance. An individual virtual machine can use at most the amount of
memory specified in its configuration file plus some overhead. 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 RAM actually used for a particular virtual machine varies as a virtual
machine runs. If multiple virtual machines run simultaneously, they work together to
manage the memory.
The recommended amount of RAM to specify for all running virtual machines is
calculated on the basis of the host computer’s physical memory and is displayed in
the memory settings slider control — Host > Settings > Memory. If you want GSX
Server to use more or less physical memory, use this slider to change the amount.
Amount of Memory Allocated to the Virtual
Machine
Additional Amount of Overhead
Needed
Up to 512MB Up to 54MB
Up to 1000MB Up to 62MB
Up to 2000MB Up to 79MB
Up to 3600MB Up to 105MB