Two years ago, I wrote a blog called “Lessons Learned with vCPU allocation“. This was still fairly early in the world of virtual desktops. But with numerous successful projects, we were able to start generating sizing estimates for virtual desktops. We talked about how many vCPUs we should allocate, how many users we expect to get per physical core, how much RAM we need and how many IOPS will we generate. I wanted to go back and see if some of the best practices I offered years ago still stand up to scrutiny. If not, I want to know why.
First, let’s look at how CPU recommendations have changed (BTW, I’m only looking at Windows 7).
| User Group | 2011 Estimate (Pooled VDI) |
2013 Estimate (Pooled VDI) |
2013 Estimate (Pooled VDI with PVD) |
| Light | 8-10 | Dual Socket: 13 Quad Socket: 11 |
Dual Socket: 11 Quad Socket: 9 |
| Normal | 6-8 | Dual Socket: 10 Quad Socket: 8 |
Dual Socket: 8 Quad Socket: 6 |
| Heavy | 2-4 | Dual Socket: 5 Quad Socket: 4 |
Dual Socket: 4 Quad Socket: 3 |
A few things to notice: We know that having a quad socket server does not scale linearly from a dual socket server. We also can see that the number of users we expect to get from a core has also increased. This basically means we can pack more users onto a server. What changed? Why are we higher now than 2 years ago? Processors have gotten faster and many of the software-based hypervisor-related instructions have been incorporated into the chip. Plus, we’ve learned to properly optimize our desktops, which will help increase user density.
Do you think anything changed with RAM recommendations?
| User Group | 2011 Estimate (Pooled VDI) |
2013 Estimate (Pooled VDI) |
2013 Estimate (Pooled VDI with PVD) |
| Light | 1-1.5 GB | 1 GB | 1 GB |
| Normal | 1.5-2 GB | 2 GB | 2 GB |
| Heavy | 4 GB | 4 GB | 4 GB |
Looks the same, which is not unexpected. We are using the same operating system, the same applications, etc.
Finally, IOPS…
| User Group | 2011 Estimate (Pooled VDI) |
2013 Estimate (Pooled VDI) |
2013 Estimate (Pooled VDI with PVD) |
| Light | 4-6 | MCS: 8 PVS: 5 |
MCS: 7 PVS: 4 |
| Normal | 8-12 | MCS: 16 PVS: 10 |
MCS: 14 PVS: 9 |
| Heavy | 25-50 | MCS: 32+ PVS: 20+ |
MCS: 29+ PVS: 18+ |
The original IOPS numbers for 2011 were based on Provisioning Services. Looking at the 2013 estimates, we are still in line with our recommendations from 2 years ago for Provisioning Services. Again, same OS and applications generating the same load.
All in all, with slight modifications to user density based on CPU, our original recommendations are still valid. You can find these latest recommendations in the Citrix Virtual Desktop Handbook, as well as so many other good best practices.
Daniel
Daniel – Lead Architect
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