IBM DS6000 Manual Do Utilizador

IBM System Storage DS6000 Series: Copy Services with IBM System z

Global Copy (formerly known as PPRC Extended Distance, or PPRC-XD) is a 
non-synchronous remote copy function for System z and open systems for longer distances 
than are possible with Metro Mirror. It is appropriate for remote data migration, offsite 
backups, and transmission of inactive database logs at virtually unlimited distances.

With Global Copy, write operations complete on the primary disk subsystem before they are 
received by the secondary disk subsystem. This capability is designed to prevent the primary 
system’s performance from being affected by wait time from writes on the secondary system. 
Therefore, the primary and secondary copies can be separated by any distance. Figure 17-1 
illustrates how Global Copy operates, and the flow is described here:

1. The host server makes a write I/O to the primary DS6000. The write is staged through 

cache and non-volatile storage (NVS).

2. The write returns as completed to the host server’s application.

3. At a later time (that is, in a non-synchronous manner), the primary DS6000 sends the 

necessary data so that the updates are reflected on the secondary volumes. The updates 
are grouped in batches for efficient transmission.

4. The secondary DS6000 returns write complete to the primary DS6000 when the updates 

are secured in the secondary DS6000 cache and NVS. The primary DS6000 then resets 
its Global Copy change recording information.

Note: The efficient extended distance mirroring technique of Global Copy is achieved with 
sophisticated algorithms. For example, if changed data is in the cache, then Global Copy 
sends only the changed sectors. There are also sophisticated queuing algorithms to 
schedule the processing of updating the tracks for each volume and set the batches of 
updates to be transmitted.

Primary (source)

Secondary (target)