tab of the previous dialog box. Notice that the Network lock manager daemon is

stopped. This could indicate that it encountered a problem by trying to start up.

Alternately, it could mean that the administrator chose to end it speci®cally because

of no need for byte range locking.

Both NFS and RPC share the same Remote Procedure Call Binder daemon.

Starting or stopping NFS will start or stop RPC, and vice versa. For example,

stopping the RPC server will end the Remote procedure call NFS daemon and may

cause NFS to stop functioning correctly.

Locks and Recovery

Clients can also introduce locks onto mounted server ®le systems. Locks will give a user shared or exclusive access to a ®le or part of a ®le. When a user locks a ®le, any process requiring access to the ®le must wait for the lock to be released before processing can continue.

There are two kinds of locks that clients can establish on all or part of a ®le: exclusive and shared. When a client obtains an exclusive lock, no other processes can obtain a lock on that portion of the ®le. When a client obtains a shared lock, other processes can obtain a shared lock to the same portion of the ®le.

Why Should I Lock a File?

A user or application can use byte-range locks through NFS to improve NFS performance. Because the NFS protocol is stateless, a given client may not be aware of changes made on the server (due to client caches). Locking ensures that this problem will not occur during critical times when the server updates ®les.

How Do I Lock A File?

An application at the client, controlled by the user, can start a lock request against a remote ®le that is mounted with NFS. The client will then send the operation to its local network lock manager Daemon through an RPC request. The client-side NLM daemon will then forward the request to the corresponding server-side NLM through RPC.

Users can call the fcntl() API (application program interface) to lock parts of ®les and specify lock parameters. For a complete description of the fcntl() API, see System API Reference, SC41-4801.

The server NLM daemon will then perform the lock operation against the corresponding ®le. The server NLM daemon generates a response that the client NLM daemon receives. The client NLM daemon generates a response for the NFS client with the results of the lock request. The NFS client will then return the result to the user through the application.

Stateless System Versus Stateful Operation

The statelessness of the Network File System does not integrate well with the statefulness of ®le locks. Problems can occur in releasing locks if either the client or server fails while their respective daemons hold a lock or locks.

74OS/400 Network File System Support V4R4

Page 91 Page 93
Page 92
Image 92
IBM AS/400E manual Locks and Recovery, Why Should I Lock a File?, How Do I Lock a File?
Page 91 Page 93

AS/400E specifications

The IBM AS/400E, now more commonly known as IBM i, is a robust and versatile midrange server that has been designed to provide a comprehensive computing solution for businesses of all sizes. First introduced in the late 1980s, the AS/400 series has undergone multiple enhancements and rebranding, with the AS/400E being one of the notable iterations. This powerful platform is closely associated with IBM's commitment to reliability, scalability, and integrated business solutions.

One of the main features of the AS/400E is its highly integrated architecture that combines hardware and software into a cohesive system. This integration allows for seamless operations, reducing the complexity typically associated with managing disparate systems. The system is powered by IBM's proprietary OS/400 operating system, which has evolved into IBM i, featuring advanced capabilities like object-oriented programming, integrated database management, and security features that are essential for enterprise environments.

A key characteristic of the AS/400E is its robust database support, primarily through the use of DB2 for i. This integrated database management system enables efficient data handling and retrieval, facilitating real-time business analytics and reporting. Furthermore, the platform supports a variety of programming languages, including RPG, COBOL, and Java, making it flexible for developers who require diverse tools for application development.

The AS/400E is also known for its exceptional reliability and uptime, making it a preferred choice for critical business applications in industries such as finance, healthcare, and manufacturing. This reliability is backed by advanced error detection and correction mechanisms, as well as redundancy features that help prevent data loss and minimize downtime.

In terms of scalability, the AS/400E can effortlessly expand to accommodate growing business demands. Organizations can increase processing power by adding more resources without significant disruption. This scalability, combined with the system’s built-in virtualization capabilities, allows businesses to optimize resource usage and streamline operations.

Security is another defining feature of the AS/400E. The platform incorporates various layers of security measures, including user authentication, encryption, and comprehensive auditing capabilities, ensuring that sensitive business data is protected against unauthorized access.

Overall, the IBM AS/400E remains a powerful tool in the enterprise computing landscape, providing businesses with an integrated, reliable, and secure solution for their technological needs. Its enduring popularity is a testament to its capability to evolve with changing business requirements while maintaining its core attributes of high performance and stability.
Top Page Image Contents