If access to a disk volume is lost, DFSMShsm can be used to perform a full-volume restore with update.

You specify ICF catalog format by including the ICFCATALOG keyword in the AMS DEFINE MASTERCATALOG or DEFINE USERCATALOG command. ICFCATALOG is the default when defining a catalog in OS/390.

VSAM data sets cataloged in ICF catalogs have the UNIQUE attribute -- their space is not owned nor managed by VSAM. Since OS/390 has an integrated Direct Access Device Space Manager (DADSM), space allocation is done through normal JCL and DADSM facilities.

Should your migration plan have a special requirement where a VSE program (prior to its conversion) has to access data that is under control of OS/390, then the data set containing this data should not be cataloged in an ICF catalog. Rather, you should then have a VSAM catalog (described in the next section) for cataloging this data set. Once the VSAM program is converted to OS/390, the VSAM catalog should be converted to an ICF catalog.

5.6.2.2 VSAM Catalogs

VSAM catalogs are supported under OS/390 but are not recommended. These catalogs can be defined to be identical in structure to VSE/VSAM catalogs. (Although identical in structure, the OS/390 VSAM catalogs contain additional information about the data sets that are defined in them; for example, data set and device attributes, data set use statistics.) OS/390 VSAM user catalogs can be accessed by a VSE system if proper measures are taken to assure catalog integrity. See 5.6.4.1, ªAccessing a VSE/VSAM Catalog from an OS/390 Systemº on page 118.

Note that this ability of OS/390 (DFSMSdfp) VSAM to process VSAM catalogs will not be available after December 31st 1999.

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IBM OS/390 manual Vsam Catalogs

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.