Forcibly Unmounting NFS Filesystems

forcibly unmounting nfs filesystems

introduction

Network File System (NFS) is an industry standard file sharing protocol that allows the

filesystems residing on one system (the server) to be seamlessly accessed from other

systems (clients) across a network. When both the client and server systems are

configured properly and performing well, NFS allows client systems to seamlessly access

remote filesystem resources as if they resided on locally mounted disks.

But what about when things are not working well, such as when the NFS server system

stops responding to requests, either because of a network partition being down, a system

panic, or a catastrophic hardware failure? In these situations, NFS filesystems can

appear “hung” on the client systems resulting in application hangs and loss of

productivity. At times like these it may be beneficial to unmount these NFS filesystems

until the server system recovers.

Of course, unmounting NFS filesystems may be less of a concern if your NFS servers

reside in a highly available cluster (i.e. ServiceGuard, TruCluster, etc.) and can recover

from hardware and software faults quickly. However, for those customers who do not

employ this level of server protection, having a mechanism available to forcibly unmount

“hung” NFS filesystems is highly desirable.

The purpose of this white paper is to describe the various tools and methodologies

available to HP-UX systems administrators to combat the situation where NFS filesystems

have become “hung” and need to be unmounted. In addition to covering the procedures

available in currently supported versions of HP-UX, this paper describes the forcible

unmount approach taken by other NFS vendors, as well as the plans to integrate official

support for forcible filesystem unmounting in a future release of HP-UX. Finally, this paper

discusses several preventative steps you can take when configuring your NFS

environment to decrease the likelihood of encountering the problem of NFS filesystem that

cannot be unmounted.