I have visited numerous customer sites where System Administrators struggle with correctly sizing and configuring their XenApp servers to run in a vSphere environment.  The most common issue I find with virtual XenApp servers is over-allocated resources.  Most of these servers were converted (P2V'd) from existing hardware, where quad-core processors and 10-20 GB of memory was not uncommon.  When approaching the question of designing the a XenApp environment, I too struggle at times with "how much of (enter resource here) is enough?".  Today, while browsing through various white papers, I stumbled upon a very helpful document put together by VMware that serves as a baseline for determining the answer to this question.  The technical document can be found here: <a title="http://www.vmware.com/files/pdf/solutions/vmware-citrix-xenapp-best-practices-EN.pdf" href="http://www.vmware.com/files/pdf/solutions/vmware-citrix-xenapp-best-practices-EN.pdf" target="_blank">http://www.vmware.com/files/pdf/solutions/vmware-citrix-xenapp-best-practices-EN.pdf</a>

While slightly dated, this article still provides valuable information for anyone constructing their XenApp environment on the vSphere hypervisor.  The key point described in the white paper is that it is much better to create numerous servers with smaller amounts of dedicated resources, as apposed to building a few "larger" virtual machines.  Typically, several servers with only 2-4 GB of vRAM and 1-2 vCPUs will perform much better (and provide better availability) than a few servers with 8-10 GB of vRAM and 4-8 vCPUs.

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