VMware VIEW COMPOSER 2.5 - ARCHITECTURE PLANNING EN-000350-01 Specifications download pdf (Page 31)

Estimating Memory Requirements for Virtual Desktops

RAM costs more for servers than it does for PCs. Because the cost of RAM is a high percentage of overall server

hardware costs and total storage capacity needed, determining the correct memory allocation is crucial to

planning your desktop deployment.

If the RAM allocation is too low, storage I/O can be negatively affected because too much memory swapping

occurs. If the RAM allocation is too high, storage capacity can be negatively affected because the paging file

in the guest operating system and the swap and suspend files for each virtual machine grow too large.

NOTE This topic addresses issues regarding memory allocation for remote access to View desktops. If users

run View desktops in local mode, on their client systems, the amount of memory used is some proportion of

that available on the client device.

RAM Sizing Impact on Performance

When allocating RAM, avoid choosing an overly conservative setting. Take the following considerations into

account:

Insufficient RAM allocations can cause excessive guest swapping, which can generate I/O that causes

significant performance degradations and increases storage I/O load.

VMware ESX supports sophisticated memory resource management algorithms such as transparent

memory sharing and memory ballooning, which can significantly reduce the physical RAM needed to

support a given guest RAM allocation. For example, even though 2GB might be allocated to a virtual

desktop, only a fraction of that number is consumed in physical RAM.

Because virtual desktop performance is sensitive to response times, on the ESX server, set nonzero values

for RAM reservation settings. Reserving some RAM guarantees that idle but in-use desktops are never

completely swapped out to disk. It can also reduce storage space consumed by ESX swap files. However,

higher reservation settings affect your ability to overcommit memory on an ESX server and might affect

VMotion maintenance operations.

RAM Sizing Impact on Storage

The amount of RAM that you allocate to a virtual machine is directly related to the size of the certain files that

the virtual machine uses. To access the files in the following list, use the Windows guest operating system to

locate the Windows page and hibernate files, and use the ESX server's file system to locate the ESX swap and

suspend files.

Windows page file

By default, this file is sized at 150 percent of guest RAM. This file, which is by

default located at C:\pagefile.sys, causes thin-provisioned storage to grow

because it is accessed frequently. On linked-clone virtual machines, the page

file and temporary files can be redirected to a separate virtual disk that is

deleted when the virtual machines are powered off. Disposable page-file

redirection saves storage, slowing the growth of linked clones and also can

improve performance. Although you can adjust the size from within Windows,

doing so might have a negative effect on application performance.

Windows hibernate file

for laptops

This file can equal 100 percent of guest RAM. You can safely delete this file

because it is not needed in View deployments, even if you use View Client with

Local Mode.

Chapter 4 Architecture Design Elements and Planning Guidelines

VMware, Inc. 31

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