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, it can affect storage I/O because too much Windows paging occurs. If the RAM allocation is too high, it can affect storage capacity because the paging file in the guest operating system and the swap and suspend files for each virtual machine become too large.
RAM Sizing Impact on Performance
When allocating RAM, avoid selecting an overly conservative setting. Consider the following:
Insufficient RAM allocations can cause excessive Windows paging, which can generate I/O that causes significant performance degradations and increases storage I/O load.
Because virtual desktop performance is sensitive to response times, VMware recommends reserving all the memory.
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
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By default, this the size of this file is 150 percent of guest RAM. This file, which is by default located at C:\pagefile.sys, causes thin-provisioned storage to expand because it is accessed frequently.
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, Horizon 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
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This file can equal 100 percent of guest RAM. You can safely delete this file because it is not needed in Horizon deployments.
- ESXi swap file
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This file, which has a .vswp extension, is created if you reserve less than 100 percent of a virtual machine's RAM. The size of the swap file is equal to the unreserved portion of guest RAM. For example, if 50 percent of guest RAM is reserved and guest RAM is 2 GB, the ESXi swap file is 1 GB. This file can be stored on the local datastore on the ESXi host or cluster.
- ESXi suspend file
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This file, which has a .vmss extension, is created if you set the desktop pool logoff policy so that the virtual desktop is suspended when the end user logs off. The size of this file is equal to the size of guest RAM.
RAM Sizing for Specific Monitor Configurations When Using PCoIP or Blast Extreme
In addition to system memory, a virtual machine also requires a small amount of RAM on the ESXi host for video overhead. This VRAM size requirement depends in on the display resolution and number of monitors configured for end users. PCoIP or Blast Extreme Client Display Overhead lists the amount of overhead RAM required for various configurations. The amounts of memory listed in the columns are in addition to the amount of memory required for other PCoIP or Blast Extreme functionality.
5K and 8K UHD resolutions are only available when using the Blast protocol and only for 1-monitor or 2-monitor configurations. If you attempt to launch a PCoIP session with a 5K or 8K monitor configured on the client, the session fails.
Display Resolution Standard |
Width (Pixels) |
Height (Pixels) |
1-Monitor Overhead (MB) |
2-Monitor Overhead (MB) |
3-Monitor Overhead (MB) |
4-Monitor Overhead (MB) |
|---|---|---|---|---|---|---|
VGA |
640 |
480 |
1.20 |
3.20 |
4.80 |
5.60 |
WXGA |
1280 |
800 |
4.00 |
12.50 |
18.75 |
25.00 |
1080p |
1920 |
1080 |
8.00 |
25.40 |
38.00 |
50.60 |
WQXGA |
2560 |
1600 |
16.00 |
60.00 |
84.80 |
109.60 |
UHD (4K) |
3840 |
2160 |
32.00 |
78.00 |
124.00 |
170.00 |
5K Blast only |
5120 |
2880 |
64.00 | 128.00 | NA |
NA |
UHD (8K) Blast only |
7680 |
4320 |
128.00 | 256.00 | NA |
NA |
For calculating system requirements, the VRAM values are in addition to the base system RAM for the virtual machine. The system automatically calculates and configures overhead memory when you specify the maximum number of monitors and select the display resolution in the console.
If you use the 3D rendering feature and select Soft3D or vSGA, you can recalculate using the additional VRAM values in a console control for configuring VRAM for 3D guests. Alternatively, and for other types of graphics acceleration besides Soft3D and vSGA, you can specify the exact amount of VRAM if you elect to manage VRAM by using vSphere Client.
By default, the multiple-monitor configuration matches the host topology. There is extra overhead pre-calculated for more than two monitors to accommodate additional topology schemes. If you encounter a black screen when starting a remote desktop session, verify that the values for the number of monitors and the display resolution, which are set in the console, match the host system, or manually adjust the amount of memory by using selecting Manage using vSphere Client in the console and then set the total video memory value to maximum of 128 MB.
RAM Sizing for Specific Workloads and Operating Systems
Because the amount of RAM required can vary widely, depending on the type of worker, many companies conduct a pilot phase to determine the correct setting for various pools of workers in their enterprise.
A good starting point is to allocate 2 GB for Windows 10 or later desktops. If you want to use one of the hardware accelerated graphics features for 3D workloads, VMware recommends two virtual CPUs and 4 GB of RAM. During a pilot, monitor the performance and disk space used with various types of workers and make adjustments until you find the optimal setting for each pool of workers.
