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Virtualization technology licensing FAQ: Hyper-V, VMware licensing

When you virtualize, don’t forget to follow the rules. Understand the virtualization technology licensing requirements for your platform and more.

Virtualization can help you save money, but it’s certainly not free. When you build a virtual infrastructure or upgrade an existing one, you’ll incur virtualization technology licensing costs.

It can be difficult figuring out which licenses you need and how much to spend on virtualization. You first have to understand the basics for your chosen platform. VMware licensing is different from Citrix XenServer and Microsoft Hyper-V licensing, particularly VMware’s new vSphere 5 licensing model.

VSphere 5 is just one example of how virtualization technology licensing is changing rapidly. VMware moved to per-VM licensing on most of its vCenter products, and cloud computing makes resource usage part of the licensing equation. Software licensing for the applications in virtual environments will have to change with the times, too, as it becomes more challenging to determine CPU usage in virtual infrastructures.

The answers to these frequently asked questions about virtualization technology licensing will help you understand the difference between per-processor and per-VM licensing, the nuances of Microsoft, Citrix Systems and VMware licensing, and how virtualization licensing will change in the future.

What are the basic VMware licensing guidelines?

When VMware released vSphere 4.1 in 2010, it moved from a per-processor to a per-VM licensing model on much of its vCenter management line. Under this model, customers can buy licenses for vCenter Capacity IQ, vCenter AppSpeed, vCenter Site Recovery Manager and the Ionix management line -- but not vCenter Server itself -- based on the number of VMs under management. This model can complicate VMware licensing, though, because the number of VMs in an infrastructure often changes.

Licensing for vSphere is still on a per-processor basis, but some details changed with vSphere 5. Now, vSphere 5 licensing costs are linked to memory usage, through virtual RAM entitlements. That means users are charged according to how much memory they assign to their VMs.

How does VMware View licensing work?

VMware View licensing comes in two different models: a bundled model or an add-on. The bundled version of this virtualization technology licensing allows you to run the number of virtual desktop infrastructure (VDI) VMs you purchased, but it also includes licenses for your VMware ESX or ESXi hosts, plus vCenter Server desktop licenses. The add-on license lets you run only the VDI VMs, leaving you to obtain the proper licenses for VMware ESX, ESXi and vCenter separately.

When it comes to VMware licensing for View, you can also choose between the Enterprise or Premier versions. The Enterprise license allows you to run the VMware View Manager and VMware View Connection server. But to run VMware View Composer, the Offline Desktop and ThinApp, you need the Premier version.

What are the basic Microsoft Hyper-V licensing guidelines?

Virtualization technology licensing for Microsoft Hyper-V is fairly simple. Hyper-V installs as a role within an existing instance of Windows Server 2008, and is included in the operating system license. However, Windows Server licenses for the guest operating system are issued per-processor, which means that the more VMs per host you have, the more Hyper-V licensing costs you’ll incur. Plus, you need Windows Server’s Enterprise or Datacenter Edition if you want to run Windows Failover Clustering with Hyper-V.

How does Windows Server licensing work in Hyper-V environments?

Licensing Windows Server instances in a physical infrastructure is fairly simple, but Windows Server licensing can get complicated in a Microsoft Hyper-V environment. Microsoft does not require client-access licenses for the OS on Hyper-V hosts, but you must still license the OSes of any virtual machines.

For example, if you install Windows Server 2008 R2 Standard Edition on a server and configure that machine as a Hyper-V host, you have not used up the server license, but server licenses are required for any VMs on that host. (You also cannot use that license to run a Windows Server 2008 R2 Standard Edition guest machine on a different host.) The Enterprise Edition license covers the host OS and up to four VMs running on a Hyper-V host, and the Datacenter Edition licenses an unlimited number of VMs (if they’re on the same host).

How does Citrix XenServer licensing work?

Citrix Systems’ XenServer is based on the free, open source Xen hypervisor. XenServer licensing also grants access to XenCenter, a free tool for basic management tasks. But if you want more advanced features such as high availability and dynamic workload balancing, you need to buy Citrix Essentials. Under this virtualization technology licensing model, you’ll have to purchase a XenServer license for each server that you manage with Citrix Essentials.

For many customers, the appeal of XenServer licensing is that it’s per-server. Simply count the number of servers on which you intend to install XenServer and multiply that by the price for the edition you’re using. This technology licensing method rewards you for good server consolidation ratios and doesn’t penalize you for RAM usage.

What are some different types of licensing models?

VMware’s per-VM licensing model applies only to its vCenter management tools. With this model, users pay for licenses based on the average number of powered-on VMs running the software over a 12-month period. The company says this virtualization technology licensing model can reduce unnecessary costs for resource-usage spikes that occurred under the per-CPU system. But per-VM licensing can also affect your server consolidation ratio, scalability and flexibility.

With a per-processor licensing model for Hyper-V’s entire virtualization platform, you can cut costs by running unlimited VMs with a single license -- such as the Windows Server Datacenter edition. SQL Server licensing also offers the benefits of per-processing model: A processor licensed for the SQL Enterprise Edition can contain any number of SQL instances.

Finally, there is VMware’s vRAM licensing model for vSphere 5. This type of virtualization licensing charges users for memory usage. Users can pool the memory allocation across an entire data center, making it possible to share vRAM entitlements among multiple hosts.

What are some software licensing challenges in virtual environments?

Virtualization changes the way we view CPU usage because applications don’t access computing hardware directly, and CPUs can be shared, scaled or moved at any time. Along with the introduction of multi-core CPUs, that makes it difficult to pinpoint exactly how many software licenses you need. It’s easy to run into software licensing violations. You might accidentally run software on more CPUs than there are licenses for, for example. Or a VM live migration to a host with different processing resources could break a software licensing agreement. In the future, software licenses may change to per-user licensing, and many vendors will alter their software licensing policies to account for the changes virtualization brings.

How will cloud computing change virtualization licensing?

Cloud computing will change virtualization technology licensing because the cloud is based on resource usage. Usage monitoring will become much more important as vendors move to a metered pricing approach. The shift to cloud computing pricing models also means admins will have to pay extra attention to virtual server sprawl, which would increase costs. For some organizations, this kind of virtualization technology licensing could reduce flexibility in their environment, with the virtual infrastructure instead based on the licensing level they can afford. Cloud computing technology licensing makes the most sense for IT shops that want to deliver on-demand services.

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