Solaris Troubleshooting NFS : NFS mounts hang, with error ” SERVER NOT RESPONDING “

Hosts remotely mount other hosts, often times via routers, bridges with  straight NFS mounts or with automount.  Sometimes, the  process accessing those remote hosts just hangs forever or gets the message:

NFS SERVER <servername> NOT RESPONDING
..sometimes followed by NFS SERVER  <servername> OK

NFS SERVER NOT RESPONDING means that many things could be at fault:

1.  The server is down or unable to respond (e.g. too busy)
2.  The network is not reliable
3.  Software or firmware problems on any component in the network, possibly  including the NFS client and/or NFS server.

For case 1, lighten the load of the server, or migrate files to a less busy server.

For case 2 and 3, we recommend the following workaround of changing mount options, as in the following  examples:

/usr/etc/mount -orsize=1024,wsize=1024,timeo=15 server:/disk /mnt  (SunOS)

/usr/sbin/mount -F nfs  -o rsize=1024,wsize=1024,timeo=15 server:/disk /mnt  (Solaris)

The 1024 read and write packet size allows NFS requests/responses to squeeze inside a single network (e.g. ethernet) packet instead of the default 8k size. The helps eliminate fragmentation across a bridge or router, as well as UDP packet reassembly, although the actual NFS performance is somewhat slower.

Increasing the initial request timeout from 7 to 15 (units are tenths of seconds) often helps in congested networks.