32.1.3.5 Migrate the SNA Network Early

If the migration plan includes converting an SNA communications network, then consider migrating ownership of the network from VSE to OS/390 within the two months that precede operating system switchover. At this time, switchover minus two months, the OS/390 system should be positioned for and nearly production ready. Assuming there is connectivity between the systems, the testing phase path has been from VSE to OS/390. After the ownership change of the network the path is from OS/390 to VSE.

This is a good task to perform as early as possible before switchover. Switching ownership of the network early provides some important benefits, including:

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Reduces the size and complexity of the conversion tasks on switchover day through dividing the conversion into smaller subtasks.

Eliminates having to fix network problems on switchover day. The operations staff get experience on the OS/390 console.

If new products such as NetView are installed the staff also gets experience with these.

Builds migration team confidence through the successful subtask conversion.

32.1.3.6 24x7 Installations

The major conversion challenge in a 24x7 installation is the limited window of allowable time for testing and switchover. Typically the biggest consumer of time during testing and switchover is the data or file migration. Therefore this is the area to focus on to achieve time reductions during conversion. Methods to shorten the window need to be found and exploited. In a 24x7 installation the impact comes from having to stop the VSE production operations during the window in which you are moving data. You can′t copy data while VSE production is running.

One additional element that increases the duration of the data transfer, is that backups should be run in case a fallback to VSE is necessary. If you migrate using tapes, then these tapes can be used. The use of tapes can be quite lengthy. One way to shorten the window where tapes are used is to orchestrate the process right down to a drill to maximize the use of the tape drives, tapes and people.

Additional testing and switchover timing considerations are:

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Time must be allotted for recovery and backout in the case of problems.

Changes to hardware configurations and JCL can increase the duration of conversion. Examples include RJE stations where you have to change the JCL in them and the configurations of the PCs that are doing file transfers.

∙Screen scraper applications are also affected. End users will be accustomed to seeing PC screens that are in ICCF format. After the switchover the screens will be in CICS or TSO formats. These need to be reconfigured within the window for switchover.

∙For large databases it may make more sense to copy disk to disk for backup and then convert the new volumes in place rather than use database utilities to move the data.

One method to expedite the data migration has been the use of extra DASD to handle the bubble associated with copying the database for switchover.

Chapter 32. Conversion Process 485

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IBM OS/390 manual Migrate the SNA Network Early, 32.1.3.6 24x7 Installations
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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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