VMware vSphere vCenter Server 4.0 - Manual (Page 29)

View Memory Allocation Information
You can use the vSphere Client to view information about current memory allocations.
You can view the information about the total memory and memory available to virtual machines. In ESX, you
can also view memory assigned to the service console.
Procedure
1 In the vSphere Client, select a host and click the Configuration tab.
2 Click Memory.
You can view the information shown in “Host Memory Information,” on page 29.
Host Memory Information
The vSphere Client shows information about host memory allocation.
The host memory fields are discussed in
Table 3-1 .
Table 3-1. Host Memory Information
Field Description
Total Total physical memory for this host.
System Memory used by the ESX/ESXi system.
ESX/ESXi uses at least 50MB of system memory for the VMkernel, and additional memory for
device drivers. This memory is allocated when the ESX/ESXi is loaded and is not configurable.
The actual required memory for the virtualization layer depends on the number and type of PCI
(peripheral component interconnect) devices on a host. Some drivers need 40MB, which almost
doubles base system memory.
The ESX/ESXi host also attempts to keep some memory free at all times to handle dynamic
allocation requests efficiently. ESX/ESXi sets this level at approximately six percent of the
memory available for running virtual machines.
An ESXi host uses additional system memory for management agents that run in the service
console of an ESX host.
Virtual Machines Memory used by virtual machines running on the selected host.
Most of the host’s memory is used for running virtual machines. An ESX/ESXi host manages the
allocation of this memory to virtual machines based on administrative parameters and system
load.
The amount of physical memory the virtual machines can use is always less than what is in the
physical host because the virtualization layer takes up some resources. For example, a host with
a dual 3.2GHz CPU and 2GB of memory might make 6GHz of CPU power and 1.5GB of memory
available for use by virtual machines.
Service Console Memory reserved for the service console.
Click Properties to change how much memory is available for the service console. This field
appears only in ESX. ESXi does not provide a service console.
Understanding Memory Overhead
Virtualization of memory resources has some associated overhead.
ESX/ESXi virtual machines can incur two kinds of memory overhead.
n The additional time to access memory within a virtual machine.
n The extra space needed by the ESX/ESXi host for its own code and data structures, beyond the memory
allocated to each virtual machine.
Chapter 3 Managing Memory Resources
VMware, Inc. 29