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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.

		FICON
		DS8000
		PPRC
ESS 750	ESS 800	FCP
		Links
Global Copy OR Metro Mirror

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

Chapter 14. Data migration in zSeries environments 303