Licensing VDI (virtual desktops) based on desktop operating systems
With VDI each user's desktop run on a centralised virtual machine (VM) on a one-to-one basis, i.e. for 50 users, you need (at least) 50 VMs.
Windows 10 EULA prohibits the operating system to be used solely for the use of VDI, even on a dedicated machine:
"Restriction: use the software as server software, for commercial hosting, make the software available for simultaneous use by multiple users over a network, install the software on a server and allow users to access it remotely, or install the software on a device for use only by remote users"
Therefore, you need a Volume Licensing agreement in place. If it is a school and they have a OVS-ES agreement then they are covered (with Software assurance - SA rights). If it is a commercial business they need either:
1) Windows VDA per device licence (4ZF-00014, for Open Value annual cost, 4XF-00014 for OVS) This would be the licence required for Thin Clients without a windows licence
2) Windows Enterprise licence with SA (Software Assurance). This would be the licence required for desktop or laptop machines with an existing licence.(KV3-00491, for Open Value, KV3-00511 for OVS - seems much cheaper).
Open Value Subscription
Open Value Subscription is an annual subscription mechanism for licencing Microsoft software (servers, desktops, Office, etc.). Microsoft describe it as:
The number of licences depends on the number of Qualified Desktops and is described as CompanyWide. Desktop licencing is done per-device. A Qualified Desktop is defined as:
Each computer will require 1, 2 or 3 of:
- Core CAL collection (to give access to server resources)
- Virtual Desktop licence (either VDA or SA, see later)
- Microsoft Office licence
If you agree to licence all 3 for each Qualified Desktop (i.e. have Office available on everything), this is described as Platform licencing and the licences are 5% cheaper. If you have fewer Office licences (or not at all), this is Non-Platform licencing; the licences are a bit more expensive, but you can save a lot on expensive Office licences.
In addition to the above, you will need a Remote Desktop Services (RDS) CAL for each device that is accessing a virtual desktop based on a server OS.
Finally, you will need Windows Server licences to cover your infrastructure, e.g. Domain Controllers, File Servers and Citrix XenDesktop delivery controllers.
In order to access a Windows Desktop operating system (e.g. Windows 7 or 10) on your device, you need either:
- VDA licence: for non-Windows devices such as tablets and thin-clients
- Windows Upgrade with Software Assurance (SA): for devices which already have Windows on, e.g. an OEM licence
Extended Roaming Rights mean that you do not need a VDA licence for accessing your desktop from a personal device outside the corporate environment. Microsoft word this as:
Example of OVS licencing for 8 devices and 2 servers (DC and desktop controller):
- 8x CoreCAL (W06-01502: CoreCAL ALNG LicSAPk OLV NL 1Y Pltfrm DvcCAL)
- 8x Office Professional Plus (79P-02338: OfficeProPlus ALNG LicSAPk OLV NL 1Y Pltfrm)
- 8x Windows Virtual Desktop rights. Any combination of:
- VDA (4ZF-00002: VDA ALNG SubsVL OLV NL 1Mth AP PerDvc) *
- Windows Upgrade with SA (CW2-00076: WinEntforSA ALNG UpgrdSAPk OLV NL 1Y Pltfrm)
- 1x Windows Server Standard (P73-05608: WinSvrStd ALNG LicSAPk OLV NL 1Y AP 2Proc)
N.B. licences marked with * above are monthly, i.e. you will need a quantity of 12 per year.
- Licensing Windows desktop operating system for use with virtual machines
- Microsoft VDI Suites & Windows VDA Frequently Asked Questions
- Understanding Open Value Subscription Pricelist
- Open Value Subscription 101
Desktop-as-a-Service (DaaS), i.e. cloud-hosted desktops
All the above Open Value Subscription licences are only relevant if you are running the virtual desktop on hardware and storage that is entirely dedicated to you. This means you cannot use them to licence virtual desktops hosted on a servers or storage that is shared with anyone else such as you would find in a datacentre. No Microsoft licence model is available that covers Windows Desktop operating systems in a shared environment.
Therefore, unless you can afford to rent or purchase dedicated hardware in sufficient quantities to give you the desired redundancy, you will be unable to take advantage of desktop as a service (even though it is technically extremely easy).
However, there is one workaround. By using Windows Server to run your virtual desktop instead of a Windows desktop OS, you can side-step the no-shared-hosting restrictions and you do not need VDA/Windows+SA licences. Citrix refer to this as Server VDI. Windows Server Datacenter licences allow you to run unlimited VMs on the hardware, so it is easier to size. You will still need a RDS CAL or VDI Suite for access.
With Server VDI on Citrix XenDesktop there are a few restrictions as the following features are not supported:
- Personal vDisks
- Hosted applications
- How Microsoft Licensing Is Throttling Desktop as a Service
- Microsoft's VDI deals make Windows Server cheapest desktop OS
- Per-user Windows licensing hurts small businesses doing DaaS