NFSv3 versus NFSv4 performance

Dear all

We recently ran a few tests using filebench with different workloads
such as varmail and others. In some cases, especially the varmail test
run, v3 performs much better than v4 with repect to the total number
of OPs handled per interval. We destroy the pool and reboot the server
after each test so there should be no dependency left. Also the
workload is big enough to fit into main memory for the client as well as
for the server. Given that we tend to use v3 for a few hundred clients
but honetsly, I expected v4 to be superior. Both client and server run
Solaris 11 with a few tweaks in /etc/system such as the number of connections, ...

For example pre-allocating 80.000 files takes about 270 seconds in v3 versus 357
in NFSv4. The total IOs for a mix of create/delete/append/... ops are

v3:
IO Summary:      6894774 ops, 11490.8 ops/s, (1768/1768 r/w)  53.4mb/s,    662us cpu/op,   4.5ms latency

v4:
IO Summary:      3084085 ops, 5139.9 ops/s, (791/791 r/w)  30.1mb/s,    921us cpu/op,  10.1ms latency

Any hints or recommendations?

Thomas