Slow VMs using Citrix Provisioning Services using VMXNet3 NIC driver

Chris Hahn made some interesting networking observations recently at a client : 

I was testing provisioned XP desktops at [CENSORED] today, and I noticed that the provisioned XP VM performance seemed very slow, though no timeouts were showing up in the target device systray application.  I had been using the new VMXNet3 network adapter, which is included with vSphere.  I switched back to the old “flexible” adapter (vlance / vmxnet), and boot times were noticeably improved.  For now I would suggest not using the VMXNet3 adapter, and check which adapter you are using if you are seeing performance issues.

Boot times (from virtual disk found PXE boot message to Windows Login screen)

XP SP3 using VMXNet3 nic – 53 seconds

XP SP3 using flexible nic – 15 seconds

Has anyone used the other types of NICs available(VMXNET 2 or the E1000)?  Let us know in the comments.