Data migration with Metro Mirror or Global Copy

	ESCON	FICON
	ESCON	Intermediate ESS 800
		Intermediate ESS 800
	PPRC
		PPRC
ESS E20s	ESCON
ESS E20s
		FCP
		Links
		DS 6000
	Links	Cascading
		Cascading
	Metro Mirror	Global Copy
		Metro/Global Copy

Figure 13-4 Intermediate ESS 800 used to migrate data with PPRC over ESCON

To utilize the advantage of PPRC with concurrent data migration, on a physical volume level though, 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 Metro Mirror between the intermediate ESS 800 and the target DS6800 disk server.

Dynamic Address Switch (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 per 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 accepted, 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.