Comments on: Citrix XenApp on VMware ESX: 1 or 2 vCPU?

By: Rob jaudon

Rob jaudon — Sun, 09 Oct 2011 23:11:16 +0000

I need some help with a some CPU constraint issues( i think) diagnosis. I have a client with a Citrix Xenapp farm (5 desktop servers/9 Application servers) spread accross 12 ESX hosts running ESX4.0. All Citrix servers, desktop and application servers have 2 cCPU’s allocated and 54% of the VM’s running on the ESX hosts are allocated 2 vCPU’s. The problem we are running into is that the Citrix Application servers are running(crawling) when trying to access the published applications. I personally think it is a multiple VCPU issue but I would like to get an opinion on if my findings are true.

Below are some screen shots from the VSphere client and esxtop readings.
My questions are what are the best practices for Citrix on ESX?
Is it typical to have multiple VCPU’s per server in a Citrix environment?
For ESXTOP readings should I be looking at the %RDY and overall performance of the host?

By: Sven Huisman

Sven Huisman — Thu, 11 Nov 2010 13:51:55 +0000

I’ve been doing some testing for project VRC (http://projectvrc.nl/) and you really should read phase II because you can read that 4 vCPU configs are most prefered. Because you can get nearly as much users on a box than with 2 vCPU machines (not overcommitting on CPU) and you therefor have less VM’s to manage.

By: Jacqui Brockwell

Jacqui Brockwell — Wed, 20 Oct 2010 08:53:55 +0000

Has anyone actually done any testing with 4 x vCPUs though? We have been running this for some time quite successfully but now I’m wondering whether we should be using 2 instead?

By: Siegfried

Siegfried — Tue, 01 Jun 2010 13:35:58 +0000

Hi,

I set 2 Vcpu on my Xenapp servers and it works better.

Thanks a lot for your article!

By: Will K

Will K — Sun, 20 Dec 2009 19:45:13 +0000

I saw similar results on my XenApp deployment but this changed drastically after upgrading to hardware with Intel Nehalem processors.

By: Andy

Andy — Wed, 04 Nov 2009 01:43:43 +0000

I’ve had mixed results depending on the workload, but still lean toward 1 vCPU … http://www.thegenerationv.com/2009/10/optimizing-xenapp-on-vmware-esx.html

By: Michael H

Michael H — Tue, 15 Sep 2009 14:21:38 +0000

I’m getting very different results compared to the vmware article – I’ve deployed XenServer 5.5 at a client running Office 2007 SP2 and Syspro. With XenServer – 20 users on the VM – 4GB, 1vCPU – Peak times CPU usage is at 10 – 20% !! Same application set different client on ESX 3.5 Update 4 – 13 users – CPU at 50 – 60% – I’ve set those servers to max at 25 users – I’m now running 6 Xenapp VM’s 2vcpu – CPU usage is high, but users arent complaining.
Bottom line is – its all over the net – XenServer outperforms ESX 3.5 when it comes to XenApp….been there done that got the t-shirt….interested to see some vSphere 4 Tests though.

By: Sven Huisman

Sven Huisman — Wed, 19 Aug 2009 09:17:05 +0000

Thanks for sharing your test-results. Strange though that VMware advises 1 vCPU per virtual server for a Citrix VM. It all depends on the applications you run, have published desktops or applications, etc. But it seems your results are similar to mine. In the end, user experience is more important then the maximum users on a box.

By: Corne Hendrickx

Corne Hendrickx — Fri, 14 Aug 2009 09:22:35 +0000

Hi Sven,

We are running a Citrix Farm with 180 machines all under VMWare. We have tested the following senarios:

1 ESX Host with 6 Virtual Citrix Servers. 1 vCPU max 22 users
1 ESX Host with 6 Virtual Citrix Servers. 1 vCPU max 24 users
1 ESX Host with 6 Virtual Citrix Servers. 1 vCPU max 26 users
1 ESX Host with 7 Virtual Citrix Servers. 1 vCPU max 22 users
1 ESX Host with 7 Virtual Citrix Servers. 1 vCPU max 24 users
1 ESX Host with 7 Virtual Citrix Servers. 1 vCPU max 26 users
1 ESX Host with 8 Virtual Citrix Servers. 1 vCPU max 22 users
1 ESX Host with 8 Virtual Citrix Servers. 1 vCPU max 24 users
1 ESX Host with 8 Viriual Citrix Servers. 1 vCPU max 26 users

We found out that is was the best configuration 1 ESX with 7 Virtual Citrix server with 22 users. These test we have done is with help of Vmware. They told us to use just one vCpu at a virtual server.

We have used this configuration for some weeks, but the employees started to complain about freezing session.

After that we have entered vCPU reservations about 200 until 400 MHz. This responded in a better user experiance.

But we still got complaints about freezing session. We have discussed the configuration with microsoft en the advised use to configure minimal 2 cpu’s for Windows 2000 and higer systems even on a virtual platform. (this is for Xen/VMware/Virtual Server.)
The reason for this is how windows divide processes on a single CPU versus 2 or more CPU’s.

After we have configured this configuration we had a very good user experiance. Even with 7 x 22 users / fysicale server. (154 on a fysicale server aind bad )

You can get a higher number of users on a fysicale server if you use a 64 bit OS that can adress more then 4 GB of memory. That is the bottele neck wy we decide to created a limit on 22 users.

The only counter that is extreemly high is the number of interrupts. But this is not a problem and is is normal if there is a heavyload on the server.

By: Rob L.

Rob L. — Fri, 06 Mar 2009 20:21:11 +0000

If your not over commiting the vCPU’s then performance should be similar to comparing single and dual cpu physical servers. Setting affinity shouldn’t made a difference either since there already is a one to one relationship between virtual and physical CPUs. The vCPU’s would have very close to 100% of a physical CPU. It’s not till there is contention for physical CPU’s that you will see performace drops for dual vCPU’s VM.