Truth about Windows Server licensing with core packs
Windows Server Core licensing is not space vehicle engineering. You need to remember a few fairly simple rules to calculate how many core licenses you need for a server.
But how Microsoft Windows Server Core licenses are sold is confusing and leaves room for interpretation. Moreover, it creates an opportunity for overpayment, often exploited by dodgy salesmen.
Let's test your knowledge
How many 16-core packs do you need to assign to two 24-core servers? Can you answer it confidently?
To avoid discussions around editions and virtualisation, please assume that these are two cluster hosts, and we are calculating Windows Server Datacenter licenses.
Do you want to know the correct answer? Then please read this article further. Or watch the video:
How to calculate Windows Server Core licenses
To license a server, you need to license all its physical cores. In addition, there are two minimums you must respect:
At least eight cores per physical processor,
At least sixteen cores per server (note: this requirement does not apply to SPLA).
See, it's simple.
We have two 2-processor servers. Each processor has 12 physical cores. Therefore, each server has 24 cores, and the total sum of cores is 48.
For the sake of the fullness of the picture, the same rules apply to System Center and Core Infrastructure Suite (CIS).
How Windows Server Core licences are sold
You cannot procure single-core Windows Server Core licences. Instead, you may be offered the following:
8-core packs (Azure subscription licences in Microsoft CSP),
These "packs" create enormous confusion.
It's "a pack of licenses", not "a license"
If you study any official document from Microsoft on Core licensing, you will inevitably notice that they only and exclusively talk about single-core licences. There is not a single mention of multiple-core licences.
However, sales and procurement deal with multi-license packs. And for various reasons, many call the license packs "licenses", e.g. "16-core license".
Based on that, salespeople invented another myth. According to them, a 16-core pack is a single license. Therefore, it's not divisible. If you listen to their logic, you may not assign core licences from a single pack to different servers or Azure virtual machines.
Let me be clear, and please excuse my language: that is total and utter bollocks.
Unfortunately, Microsoft's own and contracting web developers played a significant negative role. Here's how packs are presented in Microsoft's official documents and on the web:
Microsoft License Statement (MLS) clearly shows single cores in the License Summary. You will see packs in Transaction Data, but the summary will always have single-core licences. And that is your entitlement – the number of single-core licences.
The optional MPSA tab on the MLS represents core packs differently, but it unambiguously calls them for what they are – packs of multiple licenses.
However, if you look at your CSP entitlement in the Microsoft Office Admin portal, core packs are called "licenses". And the same mistake exists in the LSP portal (explore.ms).
So, what is right? What's the proper interpretation? Here's the rule. In any confusing situation, your "golden reference" is Microsoft Product Terms. Microsoft's licensing agreements refer to it as the official terms and conditions document. And it only talks about calculating the quantity of single-core licences. No packs. No multi-core licences.
The wrong answer
Let's get back to our original question. How many 16-core packs do you need for two 24-core servers?
You may be tempted to purchase four 16-core packs following the broken logic and outright bad advice.
However, now we know that core packs are divisible, and you only need three 16-core packs.
But even that answer is flawed.
The correct answer
Strictly speaking – and licensing requires precision – the initial question is incorrect. It should have been, "How many licenses do you need for two 24-core servers?".
Then, the answer would be clear from the start: 48 core licences.
How you purchase them doesn't matter, then. You may buy the core licences using any combination of core packs, for example:
Three 16-core packs,
Six 8-core packs,
24 2-core packs,
Or even a mix of different core packs.
If you are still confused
If you're an end customer, if somebody is still passionately telling you, "No, you cannot break 16-core packs", please show them this article.
And if they are still unconvinced, I'd like to talk to them to understand their motivation.
And, of course, please don't hesitate to send us your questions, including the ones about Windows Server Core licences for your data centre or Azure.