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Table Of Contents
Estimating Memory Requirements for Virtual Machine 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 Windows paging
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.
RAM Sizing Impact on Performance
When allocating RAM, avoid choosing an overly conservative setting. Take the following considerations
into account:
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Insufficient RAM allocations can cause excessive Windows paging, which can generate I/O that causes
significant performance degradations and increases storage I/O load.
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VMware ESXi supports sophisticated memory resource management algorithms such as transparent
page 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.
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Because virtual desktop performance is sensitive to response times, on the ESXi host, 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 ESXi swap files.
However, higher reservation settings affect your ability to overcommit memory on an ESXi host 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 ESXi host's file system to locate the ESXi
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 View Composer 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.
For instant clones, any guest operating systems paging and temp files are
automatically deleted during the logoff operation and so do not have time to
grow very large. Each time a user logs out of an instant clone desktop, View
deletes the clone, and provisions and powers on another instant clone based
on the latest OS image available for the pool.
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.
Chapter 4 Architecture Design Elements and Planning Guidelines for Remote Desktop Deployments
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