Benefit of ESXi host with two physical CPU

[sinclairj]

I know two physical server will need two cpu license. But I am not sure how it will improve the performance. Means I have two quotation 2 CPU with (8 core each) and one CPU ( 16 core).  RAM is same for both server.

[vXav]

I tend to prefer high core count as your server ends up being cheaper if you look at the $/core of your server+license.

I asked a while ago on Yellow Bricks if two 10 core CPUs are better than one 20 core CPUs and Duncan Epping said it isn't.

So what would make you prefer a 2 socket server against a one socket?

• Amount of RAM needed (usually 384GB per CPU, depends on server)
• Number of PCI lanes
• Essentials / Essentials + kits (3 x 2 CPU licenses)

I did the exercise a while ago about 2 sockets vs 1 socket if it is of interest to you.

[depping]

It definitely isn't necessarily better indeed, it will fully depend on the type of VMs and applications running. If you don't need the two CPUs, why pay the extra money?

[sinclairj]

Thanks for response. Cost difference is not much (approx difference 50K INR) and  we are going to buy one server only. I  am looking for the overall performance. Some guy told me it will be better to have two CPU as it will improve memory handling.  and if one CPU becomes bogged down, the host can use the other CPU to continue to run the system. Please advise.

[vXav]

On paper I guess he's right. Below is only my take on the matter, no official statement whatsoever.

If one CPU is "bogged down" I think you will have pressing matters with your server/motherboad to take care of anyway.

As for the performances, for virtualization you should think in terms of physical cores rather than CPU sockets. There are 2 parts to it (that I can think of):

• You won't see an improvement (at equivalent configurations; same core count, same clock speed, same amount of memory...). You might even see performance degradation if NUMA nodes are misaligned and the VM tries to access memory pages handled by the other CPU.
• However, generally the higher the core count, the lower the clock speed. So if you can work with 28 cores @2.2GHz you'll be fine with one CPU. If you need 28 cores @3.5GHz, you'll need 2 sockets.

As always it is an annoying "it depends"