NFS problem

I am copying a 'disk image' to an NFS mounted volume.

I'm using:

dd if=/dev/ad0 of=Disk.img

After dd completes the number of blocks indicated is what the raw disk 
device should
be. However, when I look at the NFS mounted image, the file size is 
anything but the
80 GB size it should be.

I have not used NFS very much in the last few years, but I don't recall 
such data loss
as being something to worry about. The NFS transactions, while using 
UDP, may be
'lost', but there was some form of retry and eventually the file data 
would be received, or
ultimately the NFS client would emit some error message.

Is there some option that I have not enabled in the kernel build, or 
well known problem
that could be the reason for this behavior.

Thanks,
John Clark.