Network Status Monitor Daemon (NSMD)

The Network Status Monitor (NSM) is a stateful NFS service that provides
applications with information about the status of network hosts. The Network Lock
Manager (NLM) daemon heavily uses the NSM to track hosts that have established
locks as well as hosts that maintain such locks.
There is a single NSM server per host. It keeps track of the state of clients and
notifies any interested party when this state changes (usually after recovery from a
crash).
The NSM daemon keeps a

notify list

that contains information on hosts to be
informed after a state change. After a local change of state, the NSM notifies each
host in the notify list of the new state of the local NSM. When the NSM receives a
state change notification from another host, it will notify the local network lock
manager daemon of the state change.

Network Lock Manager Daemon (NLMD)

The Network Lock Manager (NLM) daemon is a stateful service that provides
advisory byte-range locking for NFS files. The NLM maintains state across
requests, and makes use of the Network Status Monitor daemon (NSM) which
maintains state across crashes (using stable storage).
The NLM supports two types of byte-range locks:
1. Monitored locks. These are reliable and helpful in the event of system failure.
When an NLM server crashes and recovers, all the locks it had maintained will
be reinstated without client intervention. Likewise, NLM servers will release all
old locks when a client crashes and recovers. ANetwork Status Manager (NSM)
must be functioning on both the client and the server to create monitored locks.
2. Unmonitored locks. These locks require explicit action to be released after a
crash and re-established after startup. This is an alternative to monitoring locks,
which requires the NSM on both the client and the server systems.
AS/400 as a Network File System Client
Several entities work together to communicate with the server and local jobs on the
NFS client. These processes are the following:
vRPC Binder Daemon. This daemon communicates with the local and remote
daemons by using the RPC protocol. Clients look for NFS services through this
daemon.
vNetwork Status Monitor and Network Lock Manager. These two daemons are
not mandatory on the client. Many client applications, however, establish
byte-range locks on parts of remote files on behalf of the client without notifying
the user. For this reason, it is recommended that the NSM and NLM daemons
exist on both the NFS client and server.
vBlock I/O daemon. This daemon manages the data caches and is therefore
stateful in operation. It performs caching, and assists in routing client-side NFS
requests to the remote NFS server. Multiple instances of this daemon can
perform tasks simultaneously.
vData and attribute caches. These two caches enhance NFS performance by
storing information on the client-side to prevent a client/server interaction. The
attribute cache stores file and directory attribute information locally on the client,
while the data cache stores frequently used data on the client.
Chapter2. The Network File System Client/Server Model 11
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