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parameter. When the target volume is larger than the source volume it is usually necessary to adjust the VTOC size on the target volume with the ICKDSF REFORMAT REFVTOC command to make the entire volume size accessible to the system.

DFSMSdss also provides full DUMP and full RESTORE commands. With the DUMP command an entire volume is copied to tape cartridges and can then be restored from tape via the RESTORE command to the new source volume. During that time all data sets on that volume are not available to the application in order to keep data consistency between when the DUMP is run and when the RESTORE command completes. The advantage of this method is that it creates a copy which offers fail-back capabilities. When source and target disk servers are not available at the same time for migration, this might be a feasible approach to migrate the data over to the new hardware.

DFSMSdss is optimized to read and write data sequentially as fast as possible. Besides optimized channel programs, which always use the latest enhancements the hardware and microcode provides, DFSMSdss also allows a highly parallel I/O pattern, which is achieved either through the PARALLEL keyword within a single job/step or you can submit more than one DFSMSdss job and run several DFSMSdss jobs in parallel.

TDMF and FDRPAS provide concurrent full volume migration capabilities, which are best described as remote copy functions for migration based on software that allows a controlled switch-over to the new target volume. As a general rule, these might be considered when the number of volumes to be migrated is in the hundreds rather than in the range of thousands of volumes to be migrated. With large migration tasks, the number of volumes has to be broken down to smaller volume sets so that the migration can happen in a controlled fashion. This lengthens the migration period, so if possible, other approaches might be considered.

Both software products are usually associated with fees or service-based fees. When the number of volumes is in the range of up to a few hundred, then standard software like DFSMSdss is an option. But DFSMSdss-based migration does not automatically switch over to the target volumes and usually requires some weekend efforts to complete. DFSMSdss is standard software and part of z/OS, so there are no extra costs for software.

The choice of which software approach to take depends on the business requirements and service levels which the data center has to follow. The least disruptive approach is to provide software packages that switch in a controlled and transparent manner over to the target device, like TDMF and FDRPAS do. When brief service interruptions can be tolerated, then the standard software is still a popular solution.

14.2.2 Software- and hardware-based data migration

Piper z/OS (an IBM IGS service) and z/OS Global Mirror are tools for data migration that are based on software, which in turn relies on specific hardware or microcode support. This section outlines these two popular approaches to migrate data.

Data migration with Piper for z/OS

IBM offers a migration service using the Piper tool, which is a combination of FDRPAS as the software used in a migration server (which is part of the service offering) that is connected to the customer configuration during the migration.

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