nfs soft mount

E4. Why do I get NFS timeouts when I mount a Linux NFS server from my Solaris NFS client?

A. You get NFS timeouts because you are using soft mounts. Normally, mounts are hard, which requires the client to continue attempts to reach the server forever. A soft mount allows the client to stop trying an operation after a period of time. A soft timeout may cause silent data corruption if it occurs during data or metadata transmissions, so you should only use soft mounts in the cases where client responsiveness is more important than data integrity. If you require the use of soft mounts over an unreliable link such as DSL, try using TCP, which is what Solaris uses by default. This will help manage the impact of brief network interruptions. If using TCP is not possible, then you should reduce the risk of using soft mounts with UDP by specifying long retransmission timeout values and a relatively large number of retries in the mount command options (i.e., timeo=30, retrans=10).

Note that NFS over UDP now uses a retransmit timeout estimation algorithm in the latest 2.4 and 2.6 kernels, which means the timeo= mount option is less effective at preventing data corruption due to a soft timeout.