I guess I’m not done yet.
Last week, I posted the latest recommendations on sizing Windows 10 and Windows 7 virtual machines for a XenDesktop environment. I received a few replies from people asking for any updates regarding Windows 2012R2.
Unfortunately, when we discuss Windows 2012R2 and XenApp, the recommendations are not as straightforward as Windows 10 and Windows 7.
- Because Windows 2012R2 will do session virtualization (where many users share the same VM but get a separate session) it makes sizing CPU and RAM more difficult.
- Because we can publish multiple resources from the same VM, we can have a mix of light, medium and heavy users on the same VM at the same time.
- Because each VM will host multiple users, our VMs will be sized larger when compared to Windows 10 and Windows 7. To size correctly, we need to align our recommendations with the nuances of the hardware.
Let’s take a look at the latest recommendations before we go into more detail.
For vCPU, you notice it is based on NUMA. What is NUMA? I recommend you read these two blogs by Nick Rintalan.
To summarize, you get the best physical server density when you have the same number of vCPU for your XenApp VMs with either the number of cores within a NUMA node or 1/2 of a NUMA node. If you go with 1/2 of a NUMA node, then you will just have two times as many VMs.
Cluster on Die is a little more complex as newer hardware chips don’t have equal sized NUMA nodes across cores. Cluster on Die is a BIOS option that balances cores equally by creating clusters of cores.
Sizing RAM is also a little different than when comparing it to Windows 10 and Windows 7. With session virtualization, like XenApp, all users share the same OS instance. Users also share the same application instances. The OS and app instances only consume RAM once. That is a huge reduction in overall RAM usage, which is why the RAM recommendations are significantly lower than the desktop OS.
Of course, the amount of RAM you allocate is going to be based on the specifics of your applications.
PVS RAM Cache
Just like with Windows 10 and Windows 7 recommendations, the PVS RAM cache is extremely valuable in a Windows 2012R2 XenApp environment. With PVS RAM Cache, we see huge reductions in IOPS for Windows 2012R2.