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298 DS8000 Series: Concepts and Architecture
14.1.4 Summary of data migration objectives
To summarize the objective of data migration, it might be feasible to not just migrate the data
from existing storage subsystems to the new storage server images, but also to consolidate
source storage subsystems to one or fewer target storage servers. A second migration layer
might be to consolidate multiple source volumes to larger target volumes, which is also called
volume folding. The latter is in general more difficult to do and requires data migration on a
data set level. Some down time is needed to move the remaining data sets, which are usually
open and active 24 hours every day. If you, for example, consolidate a storage group with
1,000 volumes to 200 volumes, the service interruptions could be few and long or frequent
and brief.
14.2 Data migration based on physical migration
Physical migration here refers to physical full volume operations, which in turn require the
same device geometry on the source and target volume. The target volume capacity is equal
to the source volume capacity or larger. The device geometry is defined by the track capacity
and the number of tracks per cylinder. The same device geometry means that source and
target devices have the same track capacity and the same number of tracks per cylinder.
Usually this is not an issue because over time the device geometry of the IBM 3390 volume
has become a quasi standard and most installations have used this standard. For
organizations still using other device geometry (for example, 3380), it might be worthwhile to
consider a device geometry conversion, if possible. This requires moving the data on a logical
level, which is on a data set level, and allows for reblocking during the migration from 3380 to
3390.
Utilizing physical full volume operations is possible through the following software-,
microcode-, and hardware-based functions:
Software-based
–DFSMSdss
–TDMF
– FDRPAS
Software- and hardware-based:
– zSeries Piper - uses currently a zSeries Multiprise® server with ESCON attachment
only
– z/OS Global Mirror (XRC)
Hardware- and microcode-based:
–Global Mirror
–Global Copy
– FlashCopy in combination with either Global Mirror or Global Copy, or both
–Metro/Global Copy
The following section discusses DFSMSdss and the Remote Copy-based approaches in
more detail.
14.2.1 Physical migration with DFSMSdss and other storage software
Full volume copy through the COPY command copies all data between like devices from a
source volume to a target volume. The target volume might be bigger than the source but
cannot be smaller than the source volume. You have to keep the same volume name and the
same volume serial number (VOLSER) on the target volume; otherwise, the data set cannot
be located any more via catalog locates. This is achieved through the COPYVOLID