In XRC configurations, different host systems can share common primary disk volumes. The system data mover collects all application updates and sends them to the secondary volumes.
Figure 1 outlines three XRC configuration variations. The major difference between these configurations is the location of the system data mover.
Each of the configurations in Figure 5. Basic XRC configurations places the system data mover at a different location, as explained in Table 1.
| Configuration . . . | Location of system data mover . . . |
|---|---|
| Configuration 1 | The SDM resides at the recovery site. |
| Configuration 2 | The SDM is on one of the application site host systems. |
| Configuration 3 | The SDM is at the primary site, but not on the primary host system itself. |
| Configuration 4 | The SDM is on the recovery system. |
Recommendation: XADDPAIRed primary volumes can remain offline when you issue the XSTART command for restart or the XADDPAIR command for suspended pairs. Utility volumes and secondary volumes must be online when you issue the XADDPAIR command. Having the utility volumes online helps to establish the path grouping that is necessary to set up XRC sessions and, if using Enhanced Readers with aliases, keep aliases bound to the utilities’ base address.
Rule: All secondary volumes must be online when the XADDPAIR command processes. You can then vary the secondary volumes offline to protect them from updates that originate from non-XRC address spaces, if needed. You can use any other non-XRC volumes on the systems at either site for local applications, as they are independent of XRC activity.