Comment 49 for bug 1006446

I have been struggling with the same problem for the last few months, and accidentally stumbled on a fix that seems to work :

1. On clients set rsize=8192,wsize=8192 in /etc/fstab

I suspect that when multiple clients are writing to the NFS4 server simultaneously and overloading the network, the TCP network congestion control only works well for rsize,wsize <= 8192 (the maximum value under Linux when the code was originally written). For single clients larger values DO provide a benefit in higher throughput, but evidently there is some kernel bug triggered when using larger rsize and wsize values under conditions of network overload.