VSE/ESA Version 2.2 included new VSAM support for compression of VSAM data sets. 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. COMPRESSED data sets defined in VSE will have to be unloaded from VSE and reloaded in OS/390. REPRO or EXPORT/IMPORT can be used for this unload/reload function.

VSAM CISIZEs and Record Sizes

Both VSE and OS/390 VSAM will select an acceptable CISIZE if none has been specified. If an unacceptable CISIZE has been specified on the DEFINE, both VSAMs will attempt to select an acceptable default. Refer to the manual DFSMS/MVS Using Data Sets, SC26-4922, for more information regarding OS/390 VSAM CISIZEs.

You will not be able to directly read a VSE/VSAM KSDS that was created with index CISIZEs that are invalid for OS/390 VSAM. You must EXPORT or REPRO the cluster from the VSE system and IMPORT or REPRO it into the OS/390 system.

The physical record size is determined during the DEFINE or data set allocation by an algorithm that includes CISIZE and DASD device characteristics. The physical record size will always be equal to or less than the CISIZE. One or more physical records will contain a control interval. Beyond that, VSE and OS/390 use different algorithms.

OS/390 uses one algorithm for data sets that are cataloged in VSAM catalogs, and another for data sets that are cataloged in ICF catalogs. The VSE and ICF algorithms are similar until the CISIZE exceeds 8K. VSE will not create a physical record size greater than 8K for VSE/VSAM releases prior to VSE/ESA 1.3. VSE/VSAM in VSE/ESA 1.3 permits physical record sizes up to 30,720 (30K) bytes, depending on device type and Control Interval size specified. The OS/390 algorithm used with VSAM catalogs will not create a physical record size greater than 4K.

In summary, to be sure you obtain the CISIZE you want, you should explicitly specify the size; that is, not take the default. For data sets where incompatibilities exist, you will need to EXPORT or REPRO the data set from the originator system and then IMPORT or REPRO it into the destination system.

VSE/VSAM-managed SAM Files

VSE SAM files in VSAM managed space (SAM/VSAM) are not supported by OS/390. OS/390 cannot access them. They may be converted to VSE or OS/390 Sequential Access Method (SAM or QSAM) data sets. With OS/390, specific track or cylinder addresses for allocation are not required as they are for VSE SAM.

The files may be ported to OS/390 by copying them to a sequential data set (tape or DASD) using a VSE utility such as DITTO. The OS/390 utility, IEBGENER, may be used to copy them under OS/390. Many VSE SAM/VSAM files are used for temporary (work) data sets. These need not be converted as their contents will not be ported to the OS/390 environment.

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IBM OS/390 manual Vsam CISIZEs and Record Sizes, VSE/VSAM-managed SAM Files

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.