I’ve written previously about Microsoft’s software licensing rules for server virtualisation but in this post, I’ll pick up on a few areas that I haven’t specifically covered before.

Just to summarise the situation with regards to Windows:

• Windows Server 2008 standard edition and later includes the right to run one virtualised operating system environment (OSE).
• Windows Server 2003 R2 enterprise edition and later includes the right to run four virtualised OSEs, as does Windows Vista enterprise edition.
• Windows Server 2003 R2 datacenter edition and later, and Windows Server 2008 for Itanium-based systems include the right to run an unlimited number of virtualised OSEs, provided that all physical processors are licensed and the requisite number of client access licenses (CALs) have been purchased.
• Each OSE can be the same, or a downlevel version of the Windows product running on the host; however a Windows Server 2003 R2 enterprise edition host is not licensed for Windows Server 2008 guests.
• Multiple licenses may be assigned to a server (e.g. multiple enterprise edition licenses to run up to 8, 12, 16, etc. OSEs – saving on the cost of licensing the OSEs individually). Standard and enterprise edition licenses can also be re-assigned between servers (but only once every 90 days) and it quickly becomes more cost-effective to use datacenter edition, with its right to unlimited virtual OSEs.
• If the maximum number of OSE instances are running, then the instance of WIndows running on the physical server may only be used to manage the virtual instances (i.e. it cannot support its own workload).
• The same licensing rules apply regardless of the virtualisation product in use (so it is possible to buy Windows Server datacenter edition to licence Windows guest OSEs running on a VMware Virtual Infrastructure platform, for example).

When looking at the applications running in the virtual environment, these are licensed as they would be in a physical environment – and where per-processor licensing applies to virtualised applications, this relates to virtual CPUs.

SQL Server 2005 Enterprise Edition allows unlimited virtual SQL servers (using the per-processor licensing model) to run in a virtualised environment, providing that SQL Server has been purchased for the physical server, according to the number of physical CPUs. Similar rules apply to BizTalk Server 2006 R2 enterprise edition.

When using Windows Vista enterprise edition as the virtualisation product (e.g. with Virtual PC) and running Office 2007 enterprise edition, the virtual OSEs can also run Office (even mixed versions).

Microsoft offers two Windows Server virtualisation calculators to estimate the number and cost of Windows Server licences for a variety of virtualisation scenarios (based on US open agreement pricing).

Looking at some of the other types of virtualisation that may be considered:

• Presentation virtualisation (Terminal Services) requires the purchase of Terminal Server client access licenses (TSCALs) in addition to the server license, the normal per-device/user CALs and any application software. There are some other complications too in that:
  • Microsoft Office is licensed on a per-device basis, so non-volume license customers will also need to purchase a copy of Microsoft Office for the terminal server if clients will use Office applications within their terminal server sessions.
  • If users can roam between devices then all devices must be licensed as roaming users can use any device, anywhere. So, if 1000 terminal server devices are provided but only 50 users need to use Office applications, 1000 copies of Office are required if the users can access any device; however, if the 50 Office users use dedicated devices to access the terminal server and never use the other 950 devices, then only 50 Office licenses are required.

Microsoft Application Virtualization (formerly SoftGrid) is only available to volume license customers.

In part 6 of this series, I’ll look at licensing for some of Microsoft’s security products.