maintain the ²VSAM Ownership Bit² in the VTOC, and the list of volumes owned by the catalog.

Under VSE, multiple VSAM catalogs can own space on the same DASD volume, as long as only one recoverable catalog owns space on that volume. This support has been provided by adding a VSE unique ²bit map² in the VSAM catalog, identifying the space that is owned by a particular catalog, on a particular volume. This is not supported with OS/390 VSAM. Only one VSAM catalog can own VSAM space on a volume. While OS/390 will prevent OS/390 jobs from creating this environment, it may not recognize shared volumes which have been imported from VSE. This can lead to catalog or data set damage if space is deleted, defined, or expanded under OS/390. Refer to the VSE/VSAM Programmer¢s Reference, SC24-5145, Chapter 10 for additional information.

OS/390 ICF catalogs do not ²own² volumes. ICF uses Basic Catalog Structure (BCS) data sets, one per catalog, to contain catalog information. It uses VSAM Volume Data Sets (VVDS), one per DASD volume, to contain information about the VSAM data sets on that volume. Thus it¢s possible to have multiple VSAM data sets on the same volume that are cataloged in different ICF catalogs. It is also possible to have more than one ICF catalog on a volume.

5.6.5.4 AMS Commands

DELETE IGNOREERROR

VSE/VSAM provides the ²DELETE... IGNOREERROR² command to DELETE a cluster that had been only partially deleted previously. OS/390 VSAM provides this function for ICF catalogs using the ²DELETE... TRUENAME² command. Also, the OS/390 DELETE VVR and DELETE NOSCRATCH commands can be used to delete partial VSAM structures.

SYNCHK Parameter

OS/390 AMS does not support the SYNCHK parameter. This was used to test VSE AMS commands by allowing IDCAMS to syntax check the commands without executing them. VSE AMS also supports other test and debugging parameters which may not be applicable in the OS/390 AMS environment.

XXL KSDS (New in VSE/ESA 2.3, greater than 4GB KSDS)

OS/390 VSAM has provided support for VSAM data sets larger than 4GB in size only for SMS managed data sets in extended format with the extended addressability attribute. These data sets must be cataloged in ICF catalogs because they are SMS managed. VSE/ESA Version 2.3 includes new VSAM support for KSDS files only which are larger than 4GB. The implementations of the two VSAM systems are not compatible, due to the differences between VSAM catalogs used by VSE, and ICF catalogs used by OS/390. XXL data sets defined in VSE will have to be unloaded from VSE and reloaded in OS/390.

COMPRESS (New in VSE/ESA 2.2, VSAM Record Compression)

OS/390 VSAM has provided support for compression of VSAM data sets only for SMS managed data sets in extended format and Compaction set to Yes. These data sets must be cataloged in ICF catalogs because they are SMS managed.

Chapter 5. Disk and Tape Storage Considerations 121

Page 144 Page 146
Page 145
Image 145
IBM OS/390 manual AMS Commands, Synchk Parameter, XXL Ksds New in VSE/ESA 2.3, greater than 4GB Ksds
Page 144 Page 146

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.
Top Page Image Contents