Posey's Tips & Tricks
How License Stacking Works in the Real World
Organizations using servers with more than 16 cores need to "stack" multiple Windows Server licenses to cover all cores, ensuring compliance with licensing requirements. Here's how.
Licensing a Windows Server for use is one of those things that probably seems really intuitive, until you actually have to do it. After all, the Windows Server installation process asks you to enter a product key, and that product key corresponds to your server's license.
The problem however, is that a Windows Server Standard Edition license is only good for up to 16 cores. The same is also true of a Windows Server Datacenter license. If your server has more than 16 cores, then you will have to "stack" multiple licenses to account for all of your server's cores. Of course, Windows Server Setup doesn't give you the chance to enter multiple product keys. So how do you license a server that contains more than 16 cores?
The first thing that you will need to do is to figure out how many licenses are actually going to be required. To do so, you will need to know how many cores your server is equipped with. The easiest way to find this information is to open PowerShell and enter this command:
(Get-WmiObject -Class Win32_Processor).NumberOfCores
If you look at Figure 1, you can see that when I entered this command, the number 28 was displayed twice. The reason why this happened is because my server contains two physical CPUs and each of those CPUs has 28 cores. As such, the server has a total of 56 cores.
[Click on image for larger view.] Figure 1. My server has 56 cores.
To find out how many licenses I need, I would divide 56 by 16, giving me an answer of 3.5. Since you can't apply half a license, I would have to round number up to the nearest whole number, meaning that this server requires four, 16 core licenses.
To assign a license to the server, open an elevated command prompt window, and enter the following commands:
Slmgr /ipk <product key>
Slmgr /ato
The first of these two commands is used to supply Windows Server with the necessary product key. The second command activates the product key that you have just entered. If you are in a situation where you have to enter multiple product keys, you would repeat these commands for each of your product keys. You can see what this process looks like in Figure 2 and 3.
[Click on image for larger view.] Figure 2. Use these commands to supply Windows Server with your product keys.
[Click on image for larger view.] Figure 3. This is how you activate a product key after installing it.
When you are done, you can verify your server's licensing by entering the following command:
Slmgr /dli
If you want to see information that is more verbose in nature, then you can use a slight variation of this command. The command to use is:
Slmgr /dlv
It is important to keep in mind that in addition to any required Windows Server licenses, you are also going to need some Client Access Licenses, or CALs as Microsoft likes to call them. CALs can be purchased on either a per user or a per device basis. In my organization for example, I opted to use User CALs because I only have a couple of users. In contrast, I have dozens of devices, so it was way cheaper to go with User CALs.
It is worth noting that if you happen to be using a Windows Server Essentials license, then things work a little bit differently. Windows Server Essentials only supports 10 cores and a single physical CPU. Additionally, Windows Server Essentials does not require the use of CALs, but you are limited to 25 users and 50 devices.
If you are using Windows Server Standard Edition or Datacenter Edition, then you are required to purchase the required number of CALs. However, you don't actually have to install those CALs (unless you are using RDS CALs, which are only used for licensing remote desktop usage). Microsoft simply requires you to keep track of the number of CALs that you own and to ensure that your user or device count is less than or equal to the number of CALs that you have purchased.
About the Author
Brien Posey is a 22-time Microsoft MVP with decades of IT experience. As a freelance writer, Posey has written thousands of articles and contributed to several dozen books on a wide variety of IT topics. Prior to going freelance, Posey was a CIO for a national chain of hospitals and health care facilities. He has also served as a network administrator for some of the country's largest insurance companies and for the Department of Defense at Fort Knox. In addition to his continued work in IT, Posey has spent the last several years actively training as a commercial scientist-astronaut candidate in preparation to fly on a mission to study polar mesospheric clouds from space. You can follow his spaceflight training on his Web site.