IBM DS6000 Series manual Global Copy PPRC-XD, Metro Mirror

	4
Server write	Write acknowledge
	Write to secondary
1
	2
	3
	Write hit
	to secondary

Figure 6-7 Metro Mirror

Global Copy (PPRC-XD)

Global Copy copies data non-synchronously and over longer distances than is possible with Metro Mirror. When operating in Global Copy mode, the source volume sends a periodic, incremental copy of updated tracks to the target volume, instead of sending a constant stream of updates. This causes less impact to application writes for source volumes and less demand for bandwidth resources, while allowing a more flexible use of the available bandwidth.

Global Copy does not keep the sequence of write operations. Therefore, the copy is normally fuzzy, but you can make a consistent copy through synchronization (called a go-to-sync operation). After the synchronization, you can issue FlashCopy at the secondary site to make the backup copy with data consistency. After you establish the FlashCopy, you can change the PPRC mode back to the non-synchronous mode.

Note: When you change PPRC mode from synchronous to non-synchronous mode, you change the PPRC mode from synchronous to suspend mode at first, and then you change PPRC mode from suspend to non-synchronous mode.

If you want to make a consistent copy with FlashCopy, you must purchase a Point-in-Time Copy function authorization (2244 Model PTC) for the secondary storage unit.

98DS6000 Series: Concepts and Architecture