Recovery of DL/I - IMS/ESA compatible databases require special procedures. Image copy, change accumulation, and log files are not compatible between DL/I and IMS/ESA. The recovering of database changes performed under DL/I must be performed using DL/I image copy, change accumulation, and log files with DL/I utilities; and the recovering of database changes performed under IMS/ESA must be performed using IMS/ESA image copy, change accumulation, and log files with IMS/ESA utilities. As such, one would probably want to take an IMS image copy prior to switching to IMS/ESA update access of the databases and a DL/I image copy prior to switching to DL/I update access of the databases.

8.1.8.2 Unloading and Reloading the Database

Should the physical database need to be migrated to MVS, and there is no requirement to access the database with DL/I after it has been converted to IMS/ESA format, the following steps should be followed:

1.Perform an unload using DL/I.

2.Translate and compile the DBDs, PSBs, and ACBs using IMS/ESA.

3.Perform a reload using IMS/ESA.

As there is no HDR2 label record on the standard tape label created by the DL/I unload utility, the DD statement for tape input to the IMS/ESA reload utility must specify blocksize and recordsize. See the DL/I Data Base Administration Guide for recommended values.

Note that secondary index creation is different for IMS/ESA (see 8.1.6, ªUtilitiesº on page 173).

The HD unload/reload must be used for HDAM, HIDAM, and HISAM.

Tape files must be used across systems and not disk when unloading and reloading. The DL/I HISAM unload cannot be used as input to the IMS/ESA HISAM reload.

You should not attempt to unload from IMS/ESA and reload using DL/I.

The AMS recordsize parameter for IMS/ESA should be CI size-7 rather than CI size-10 when you define the cluster to VSAM. The IMS/ESA DBD generation will provide suggested parameters. The segment prefix for index databases is one byte shorter for IMS/ESA.

The following flow chart depicts the steps to be taken in migrating your databases, with or without compatibility, and in generating your IMS/ESA system.

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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.
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