Citrix Terminal Server Sizing, vCPUs to number of users
Posted on 2014-10-20
Just after guidance on the sizing of terminal servers and the number of users per terminal server.
The terminal servers we run are Windows Server 2008 R2 with XenApp 6.5 virtualised using VMware 5.0 on Cisco blade servers. Blades have 2x Xeon E7-2870 processors installed (20 physical processors, 40 logical) and 496GB of RAM.
We have 4 vCPUs per server and 12GB of RAM per server, and we were having problems with CPU contention on the terminal servers, with CPU spikes to 100% causing the terminal servers to pause. RAM is never fully utilised and is not a concern.
To resolve the issue with CPU contention, we continually added more terminal servers, reducing the number of users on each server, to the point where we now have only 8-12 staff per terminal server, still with occasional pauses due to high CPU usage on the servers. We currently have a total of 83 terminal servers.
Excel 2010 seems to be the biggest culprit for CPU usage, as we are supporting a financial services firm using a lot of very large Excel spreadsheets and this will often also be used to pull data from the core accounting application which uses an SQL back end.
Windows DFSS is enabled on the servers, though this does not seem to have any effect on the issue.
CPU usage on the VMware hosts is all OK, with usage during business hours hovering between 65-75%, occasionally spiking as high as 80%
Previously, we had physical servers running 4 CPUs and 12GB of RAM on Server 2003 R2. The previous terminal server farm supported the same number of users with only 32 terminal servers for the same staff.
My questions are as follows:
Should we reduce the number of terminal servers that we are running, but increase resources available to them? (approx. 40 servers with 8vCPUS and 24GB of RAM or 60 servers with 6vCPUs and 18GB of RAM)
Are there any other suggestions that people may have to prevent high CPU usage causing a terminal server to pause for all users?
What ratio of users to terminal servers are other people running in similar environments?