Citrix XenApp on VMWare

A few years ago, there was a lot of discussion regarding Citrix XenApp/Terminal Server running on VMWare. Our personal experience was that it wasn't that good, and with anything above a few (4-5) concurrent users performed terrible when doing day to day tasks. We even tried the tweaks that were going around (stuff like only use 1 vcpu on your Citrix server, and various other tweaks going around). Our general feeling was to not do it anymore, and left it at that.

However, time goes on, and technology moves forward. But the articles remained online, and no one really talked about the advancements that have been made. Then, on VMWorld 2009 there was a session about running XenApp using vSphere. If you create a (free) account on vmworld.com, you can watch it for free

Basically, a few best practices are given:

1. Use the newest CPU's in your hosts (Nehalem architecture or higher). So if you are still using older hosts (like HP G5 series servers) then think again. The newer CPU's alone would give about 30% better performance (according to the video, ymmv)
2. Use vSphere, mainly because it supports MMU virtualization which gives a good performance boost for Xenapp (but if you are still on ESX3.5, you *really* should be thinking of upgrading anyway, instead of thinking of virtualizing your Xenapp servers)
3. The usercount on a VM will never be the same as on a physical server. The idea is to be running multiple smaller VM's and thereby getting more users in total per physical box.
4. Don't use p2v'd systems. It's much better to start with a clean OS, but if you must, remove old hardware, hardware management agents, and unused OS features (wallpaper, menu animations, systemtray animating things such as network indicators and system clock. Of course there are other tweaks you always need to do for any terminal server environment.The sweetspot of the Xenapp VM's is often  2vCPU's and 4GB RAM. More vCPU's will usually give less performance.
5. Old blogposts are no longer valid, so tweaks like "disable page sharing and memory ballooning" are no longer necessary.
6. Use realistic tests. It's no good if your environment performs well in synthetic tests if the applications that the users will use are not performing up to par.

The video also has someone from eBay giving a talk about their environment, and they came to 6 to 8 users per VM, each with 2vCPU's and 4GB RAM, running 10 VM's on one DL380G6. Like I said, the video is free to watch, and highly informative.