Vmotion cause virtual machine to be slow

[Guv]

We are using ESX 3.5 and virtual centre 2.5. We have an issue with vmotion when some of our virtual machines are being vmotion the access to the virtual machines becomes slow. The virtual machines in question are windows 2003 terminal servers. They have the latest vmware tools installed. The virtual machine in question have 4 virtual CPU's and 4 GB memory. We have 3 ESX servers in a cluster with DRS enabled. When the virtual machine is vmotioned. users complain slow access. What would cause the slowness during vmotion. Would it be lack of resources on the ESX Servers hosts such as on the service console not having enough memory. Is there any other reasons why it would be slow. When they are not being vmotion access is fine.

We have about 3 ESX servers. One ESX Server has 2 Processor Sockets, 2 Processor Cores per socket and so have 8 logical processors. Hyperthreading is enabled. The other ESX servers has 2 Processor Sockets and 1 Processor Cores per Socket and therefore has 4 Logical Processors. Could this cause any issues.

[weinstein5]

What you are experiencing I believe has to do with the fact that you have 4 vCPUs for the VM - best practice is you should have at least twice the number of cores as the number of vCPUs - so each host in the cluster should have at least 8 cores - I would consider droppping the number of vCPUs down to 2 to see if that improves the perfomance of the TS sessions -

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[RParker]

In addition to what weinstein said the Memory also could be a factor. It has to transfer the contents of the Memory (4Gb worth) across the network to the other machine while the VM is still in operation.. That could also contribute to 'slow' performance during Vmotion.

You may have some issues with either your NIC's (are they embedded?) your switches (are they enterprise level Ethernet Switch?, and are they setup properly) or the configuration for the vSwitch on the ESX servers (jumbo frames, no jumbo frames, are they on the same segment as iSCSI traffic or high IO, etc...) .

There are many variables here, but CPU (do you really need 4 vCPU?!?) and Memory are obvious factors.