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XenServer VM Citrix Worker sizing question

Oliver Ollivetti




I trying to figure out the best option for sizing my virtual XenApp Worker Server on our new hardware.

One XenServer host has 2x12CPU and 256GB Ram. 

I have allocated 8GB Ram to Xenserver Dom0 on each of our 4 hosts. 


After reading some "Best Practice" configurations I would come the the following result:

- 24pCPU \ 4 NUMA Nodes = 6pCPU per NUMA


VM optimum:

8x VM with 6vCPU (2xSockets \ 3 Cores) 32GB RAM


I would prefer 

4x VM with 12vCPU (2xSockets \ 6 Cores) 64GB RAM


Does this make sense?

I would overcommit RAM as because I have allocated 8GB to xenserver I only have 248GB available. Does this matter. Do I have to reduce to 30\62GB RAM?


Thank you for your help. Best regards

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You have 12 cores and do you have hyperthreading enabled? Also note that with 2 PCPUs (physical CPUs), your RAM will be split between two NUMA nodes (128 GB, each) plus your dom0 is going to take up some space on one of them, so factor that in, as well since as soon as any VM cannot fit on the 128 GB associated with one NUMA node, it will force vNUMA to kick in and split the memory and VCPUs, even if there is enough room on one CPU to accommodate all the vCPUs of that VM. In your case, that means you're already down to 120 GB on that one CPU. If you migrate VMs around, that should also be considered as where the VMs reside will change depending on the circumstances.


Optimization may take come experimentation. You make want to try several combos.



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thank you for your response.

We have 2x 12 cores and hyperthreading enabled too. Further we have 4 NUMA nodes on that server.

So actually I would have 6 cores and 64GB Ram for each NUMA section. As hyperthreading enabled I should have 48vCPUs as seeen in the management.

I will have a check on cugc.


After reading some more it would now come to the following result:

2x12pCPU with Hyperthreading => 48vCPU. Oversubscription ratio 1,5:1 would result to 36vCPU.

I could make 6 server with 6vCPU (2Sockets\3Cores) which results in 36vCPU



If I remove 8GB Ram for Xen Dom0 I have 248GB left. Dividing this by 6 results in 41,333. Well I would configure 38GB per VM.


Does this make sense....



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