Specifications

CHAPTER 6 Performance Tuning and the VMware GSX Server Host
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Understanding Memory Usage
GSX Server allows you to set the memory size of each virtual machine and the amount
of the host computer’s memory that can be used for virtual machines. A third control
governs the extent to which you want to allow the host operating system’s memory
manager to swap virtual machines out of physical RAM.
By adjusting these settings, you can affect both virtual machine and overall system
performance.
This section describes how GSX Server uses the memory configuration parameters to
manage virtual machines and system memory properly. For information on memory
use for a specific virtual machine, see Allocating Memory to a Virtual Machine in the
VMware GSX Server Virtual Machine Guide.
Memory Use on the Host
Host operating systems do not behave well when they run low on free memory for
their own use. When a Windows or Linux host operating system does not have
enough RAM for its own use, it thrashes — constantly swaps parts of itself between
RAM and its paging file on disk. To help guard against virtual machines causing the
host to thrash, GSX Server enforces a limit on the total amount of RAM that may be
consumed by virtual machines.
In general, the sum of the memories of all currently running virtual machines plus
overhead for the GSX Server processes cannot exceed the amount of physical
memory on the host minus some memory that must be kept available for the host.
For more information, see Using Additional Memory on page 186.
Some memory must be kept available on the host to ensure the host is able to
operate properly while virtual machines are running. The amount of memory reserved
for the host depends on the host operating system and the size of the host
computer’s memory.
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