5.6.4.1 Accessing a VSE/VSAM Catalog from an OS/390 System

Your migration plan might include the requirement to access VSE/VSAM

catalogs from the OS/390 system. Under no circumstances should you attempt to share VSAM catalogs or data sets between OS/390 and VSE/VSAM concurrently. There is no system data integrity provided for concurrent access sharing. Loss of data may occur. If OS/390 access to a VSE/VSAM catalog is necessary, the following procedures should be used:

1.Execute the VSE AMS command EXPORT DISCONNECT to disconnect the VSE user catalog from the VSE master catalog.

2.Execute the OS/390 AMS command IMPORT CONNECT to connect the VSE user catalog to the OS/390 master catalog.

3.An OS/390 AMS DEFINE ALIAS command may be necessary to reestablish OS/390 ALIAS name structures for that user catalog.

The catalog and data are now ready to use with OS/390 applications. (Note: Suballocated VSAM space may be accessed through OS/390 VSAM catalogs. However, OS/390 VSAM catalogs do not support non-VSAM data sets in VSAM space; that is, a VSE facility usually used for VSE/VSAM-managed SAM files.)

²Reversing² the above procedure allows VSE access to the catalog once again. This is accomplished by:

1.Execute the OS/390 AMS command EXPORT DISCONNECT.

2.Execute the VSE AMS command IMPORT CONNECT.

The catalog and data are again ready to use with VSE applications.

DISCONNECT does not prevent access by VSE of OS/390 applications which already have access to the catalog or data sets defined in the catalog. Care must be taken in implementing procedures to make sure the catalog is properly closed in OS/390. In VSE, catalogs are never actually closed, but can be disconnected to prohibit access. In OS/390, you can find out which catalogs are open by using the MODIFY CATLOG command. See the manual Managing Catalogs, SC26-4914 for more information.

You may also access an OS/390 created VSAM user catalog from a VSE system by disconnecting the catalog from the OS/390 system and then connecting it to the VSE system. The procedure is the same as that described above.

Under no circumstances should you attempt to share VSAM catalogs or data sets between OS/390 and VSE/VSAM such that more than one system can perform updates concurrently. Read-only sharing may be permitted. See 5.6.6.3,

ªCross-System and DASD Sharingº on page129 for more detail.

5.6.4.2 Converting VSE/VSAM Catalogs to OS/390 ICF Catalogs

The OS/390 AMS CNVTCAT command converts a VSAM catalog to an OS/390 ICF catalog. After you are sure that VSE will not need to access the VSE catalog(s), they may be converted to ICF format.

Non-VSAM files in VSAM managed space must be deleted before running CNVTCAT. If the VSAM catalog has VSAM clusters defined in sub-allocated space, they will be converted to UNIQUE space during the conversion. All volumes owned by the catalog should be backed up before running CNVTCAT. See Managing Catalogs, SC26-4914, chapter 9 for more detailed information.

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IBM manual Accessing a VSE/VSAM Catalog from an OS/390 System, Converting VSE/VSAM Catalogs to OS/390 ICF 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.