Intel X540 T2

[Ryan Stone]

This sounds like it might be the issue where large NFS transfers over
TSO exceed the maximum number of segments supported by ixgbe (or other
drivers).  There is a thread on it:

http://lists.freebsd.org/pipermail/freebsd-net/2014-January/037694.html

Workaround would include:

- Disable TSO on the ixgbe port with "ifconfig ix0 -tso".  There would
be a performance impact on the NFS server.
- Decrease rsize/wsize parameters on the ESXi client mounts to 32K or
lower.  There would be a performance impact on both the NFS server and
the clients.