Open System Services NFS Management and Operations Guide

6 OSS NFS Reliability
This chapter describes OSS NFS configuration issues and reliability features.
How OSS NFS Implements Reliability
The operating system implements the underlying component-level reliability for the OSS NFS
subsystem. Moreover, the NFS protocol is a reliable message protocol that allows clients and
servers to lose connectivity without affecting data integrity.
Important OSS NFS and operating system reliability features are:
• The fault-tolerant operating system provides:
Mirrored disk volumes◦
◦ Backup processors
◦ System process pairs
• The OSS NFS subsystem is highly available:
The OSS NFS manager runs as a process pair.◦
◦ The OSS NFS port mapper runs as a process pair.
◦ STYPE OSS server processes and the LAN interface process are persistent; that is, they
are automatically restarted by the OSS NFS manager process.
◦ All configuration and data files can reside on mirrored disks.
• OSS NFS uses a transaction cache to assure consistent responses to duplicate or retried
requests.
NFS Protocol Operations
NFS is a stateless protocol. The parameters of each remote procedure call contain all the information
necessary to complete the call, and the server does not keep track of any past requests. When a
server shuts down, the client resends NFS requests until the server restarts and responds. When a
client shuts down, no recovery action is necessary for either the client or the server, because the
client loses context.
OSS NFS servers maintain request caches to improve performance:
• The LAN interface process and PCNFSD process cache recent and in-process requests. As a
result, quick response can be provided to duplicate requests, and retries receive the same
result as the original request. This cache is shared by all requests going through the same LAN
interface process and PCNFSD process; it is cleared whenever the LAN interface process or
PCNFSD process is stopped and restarted.
• The OSS name server also keeps a history of recent OSS NFS requests that are not duplicates.
This history helps ensure consistent responses to duplicate requests that are not detected by
the LAN process.
• To ensure the integrity of the OSS file system, the OSS name server also keeps a record of
mounted filesets, in-process DDL operations, and its own process name.
66 OSS NFS Reliability