As we had continuing severe problems with our applications, I downgraded the entire nfs-kernel-server and nfs-utils packages to version 1:1.2.5-3ubuntu3 using "apt-get install nfs-common=1:1.2.5-3ubuntu3" and "apt-get install nfs-kernel-server=1:1.2.5-3ubuntu3".
The I/O problems are gone with this older version.
As we had continuing severe problems with our applications, I downgraded the entire nfs-kernel-server and nfs-utils packages to version 1:1.2.5-3ubuntu3 using "apt-get install nfs-common= 1:1.2.5- 3ubuntu3" and "apt-get install nfs-kernel- server= 1:1.2.5- 3ubuntu3" .
The I/O problems are gone with this older version.