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Windows Server Licensing..... :-/

This is just a note-to-self, but if its useful to others, thats cool.

When you first start trying to work out what these licenses allow you to do, its all a bit complicated and overwhelming (partly cos there's a lot of confused "information" out there because the licensing and SKUs changed quite drastically).

As far as I can work it out, it boils down to this;

  • Standard and DataCenter are the same in terms of what is "in the box"
  • The difference between the two Editions is the number of virtual instances you can run on the licensed Server
  • Licences apply to a specific physical system
  • The number of licenses you may need is governed both by the number of physical CPUs (not cores or hyperthreaded psuedo-cores) in the system and by the number of virtual instances you are going to be running concurrently on that system
  • For physical CPUs, a single license of either Edition covers up to 2 physical CPUs
  • Multiple licences can be applied cumulatively to a single system
  • If you have system with more than two CPU sockets populated you can add additional licence(s) for the extra CPUs:
    • Divide the number of CPUs installed by 2 to get the number of licenses required for a system (and round up)
    • A 3-way SMP system would need 2 licenses (2 x 2 CPUs to cover up to 4 physical CPUs)
    • If you have one 3-core CPU, you only need one license to cover the one physical CPU. This is still true if the CPU features hyperthreading and thus presents 6 psudeo-cores
  • There is an absolute limit to the number of physical CPUs that can be licensed
    • This is either 320 CPUs or 320 licenses (for 640 CPUs)... I don't think I'm ever going to run into this limit though!
  • With regards to virtualisation, one Standard license lets you have two OS instances running on the licensed system, while one DataCenter license lets you have unlimited OS instances
    • It is worth noting that there is a point where cumulative Standard licences become less cost-effective than a single DataCenter licence. Under US pricing at Server 2012 launch, this was around 5 Standard licences (for 10 VMs)
  • There is a caveat with regards to virtualisation and Standard Edition; a Standard Edition machine that is running virtualisation software (whether it is Hyper-V or some other product, such as VirtualBox) may have two virtualised Standard Edition instances running as well as the 'host' (bare metal) instance that is running that virtualisation software but only if the 'host' instance is only running the virtualisation software and the tools and services required to operate and manage it:
    • Things like multipath I/O and iSCSI can legitimately be used if they are required in order to manage and/or run the virtualised instances
    • If the bare metal instance hosts a general purpose file Share (for example), then it is in breach of licensing
  • Hyper-V Replicas count as distinct VMs
  • Clusters require each host to be licensed for its full compliment of CPUs and for every VM in the cluster
  • Licences do not migrate with a VM, the migrated-to system must have a licence available to run the migrated VM
  • Licenses cannot be split
    • a Standard licence doesn't allow two single-CPU systems to run one instances of Server each; the licensed CPUs must be in the same system
    • one Standard licence cannot be used to licence one virtualised instance on each of two different systems
  • For 'blade'-type systems, each individual blade counts as a system that requires licensing
  • Non-OEM licences may allow for reusing a licence in the event of a hardware failure, but check the EULA
  • Software Assurance does a few magic things, like granting downgrade rights and licensing Replicas
  • Volume Licensing also has some magic regarding licence transferability... but I can't remember what and I can't find the page I read about it on

A key term to note is "running instance;" according to this Microsoft document (which is specifically linked to from the Windows Server 2012 R2 Licensing Datasheet), "Use terms for each software license specify the number of instances of software that you may run on a particular server at a time, rather than the number of copies of the software that you may install and use on your server" [emboldening added for emphasis], so it appears that with Standard Edition, you can actually have more than the 2 virtual instances set up, just so long as you never, ever, ever simultaneously run more than the 2 instances the license entitles you to run... BUT having read a few articles, it is clear that even Microsoft's own writers (and presumably their writer's technical- and proof-readers) don't fully understand their own licensing scheme, so while this is published licensing information, it may not actually be what the Microsoft Legal Department think the licensing means!