I am thinking the issue may be down do the creation of virtual switches , however I would have expected other peoples web servers to have experienced this phenomenom.

There are spare cores for the host to utilize, is ESX work this way?

I believe that it is recommended to split heavily loaded web servers across ESX boxes, do you know the reason for this?

I ran with affinity set so as to compare the performance difference from Physical box (single core) to ESX box single core. I also ran the test without affinity set and got the same performance.

We have 2 gigs of memory per VM, during peak load less there is more than a gig free on each VM.

There is a NIC shared for 14 ESX boxes. When I place the other VMs on a separate ESX box, using the same NIC the problem goes away. I therefore can't see how it can be NIC related.

The Web Server CPU is at 100% for both tests so it doesnt appear that the network is bottlenecking the Web Server.

If the other servers on the ESX box are not network intensive, but high on CPU (factorial calc on each) there is no problem!

Is it normal practive to have multiple servers which have heavy network I/O (and simultaneously high CPU) on a single ESX box? (NOTE -even when there are several spare cores for the ESX box)