"I have a low NFS performance in VMware environment."
Tests conducted with DSS and IOMeter: while doing 16K Reads and with parameters as specified in "Comparison of Storage Protocol Performance" documentation from VMware, Read performance for iSCSI and NFS is ~110 MB/sec. Also, while performance for 16K Writes on iSCSI is ~70 MB/sec, NFS Write performance is very slow.
Unchecking "Synchronous" box and running IOMeter Write test reports ~100 MB/sec for NFS - same as for iSCSI. Also, cloning 8 GB test VM and gives results comparable to same operation performed via iSCSI - just under 3 minutes or 50 MB/sec.