One of the age old questions in the Server Based Computing industry is "how many users can I get on a XenApp server?". The answer has always been "it depends", but we knew some general rules of thumb. Now, throwing server virtualization in the mix, that question is all that much harder to answer. Luckily, there is a new Citrix guideline written by Andy Baker to help determine optimal VM configurations.
In most situations, testing has shown that optimal scalability is obtained when 4 virtual CPUs are assigned to each virtual machine. When hosting extremely resource intensive applications, such as computer aided design or software development applications, user density can sometimes be improved by assigning 6 or even 8 virtual CPUs to each virtual machine.
The user density of each 4vCPU virtual XenApp server will vary according to the workloads that they support and the processor architecture of the virtualization host:
- Dual Socket Host: You should expect approximately 36 light users, 24 normal users or 12 heavy users per XenApp virtual machine.
- Quad Socket Host: You should expect approximately 30 light users, 20 normal users or 10 heavy users per XenApp virtual machine.
The amount of memory assigned to each virtual machine varies according to the memory requirements of the workload(s) that they support. As a general rule of thumb, memory requirements should be calculated by multiplying the number of light users by 341MB, normal users by 512MB and heavy users by 1024MB (this number includes operating system overhead). Therefore, each virtual machine hosted on a dual socket host should typically be assigned 12GB of RAM and each virtual machine hosted on a quad socket host should be assigned 10GB of RAM.
For more details, check out the article at the source...