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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.
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This topic addresses issues regarding memory allocation for remote access to View desktops. If users
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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
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significant performance degradations and increases storage I/O load.
VMware ESX supports sophisticated memory resource management algorithms such as transparent
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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
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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
Windows hibernate file
for laptops
VMware, Inc.
By default, this file is sized at 150 percent of guest RAM. This file, which is by
default located at
C:\pagefile.sys
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.
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
, causes thin-provisioned storage to grow
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