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Chapter 14. Data migration in zSeries environments 303
To utilize the advantage of PPRC with concurrent data migration on a physical volume level
from older ESS models like the ESS F20, an ESS 800 (or in less active configurations an
ESS 750) might be used during the migration period to bridge from a PPRC ESCON link
storage server to the new disk storage server which supports only PPRC over FCP links. The
approach is Metro/Global Copy with the ESS 800 in between hosting the cascaded volumes,
which are PPRC secondary volumes for Metro Mirror and at the same time also PPRC
primary volumes for the Global Copy configuration. It is recommended that you connect the
intermediate ESS to a host whether it is over ESCON channels or FICON channels. This
allows the ESS 800 to off-load messages to the host as well as to manage the PPRC volumes
within the intermediate ESS during the migration period.
The actual setup and management might be performed through the ESS GUI with its Copy
Services application. Another possibility is to manage such a cascaded configuration with
host-based software like ICKDSF or TSO commands, when the TSO command support for
cascaded volumes is available. Otherwise use a combination of TSO commands and ICKDSF
for just defining the cascaded bit when setting up Global Copy between the intermediate ESS
800 and the target DS8000 disk server.
Dynamic Address Switching (P/DAS) for a non-disruptive application I/O switch from the old
hardware to the volumes in the new hardware is not possible in this configuration because
P/DAS requires the PPRC secondary volumes to be in a DUPLEX state. PPRC-XD stays, by
definition, always in PENDING state. Theoretically it is possible to switch from PPRC-XD to
Synchronous PPRC and replicate the data twice over Synchronous PPRC, which may
impose significant impact to write I/O to the old hardware. It is usually quicker and less
difficult, when a brief application down time is acceptable, to switch from the old hardware to
the volumes in the new hardware.
Again this approach is only possible from IBM ESS to IBM DS6000 or IBM DS8000 disk
storage servers and it requires the same size or larger PPRC secondary volumes with the
same device geometry.
Data migration with Metro Mirror or Global Copy
A variation to the approach discussed above is to use straightforward Metro Mirror or Global
Copy from the ESS 750 or ESS 800 to the DS8000.
Figure 14-5 Metro Mirror or Global Copy from ESS 750 or ESS 800 to DS8000
Metro Mirror (Synchronous PPRC) provides data consistency at any time once the volumes
are in full DUPLEX state, although through its synchronous approach it imposes a slight
FICON
PPRC
Links
FCP
Metro Mirror
ESS 750
Global Copy
ESS 800
OR
DS8000