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Chapter 14. Data migration in zSeries environments 299
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.