(Particularly on 1Gps links)
Ensure at least 2 paths to each device, and set each path to Round Robin.
Set disk max IO to 512 from 32k
https://kb.vmware.com/kb/1003469
Set Round Robin max IOPS to 1 from 1000:
https://kb.vmware.com/kb/2069356
iSCSI Performance improvements for VMware
