Sharing volumes with TrueCopy

Like UR, the TC remote replication function provides copies of production volumes in a second location. However, unlike UR, the TC S-VOLs are synchronous copies of the P-VOLs, and the secondary storage system is located in the same general region as the primary storage system.

Creating a UR backup and a TC backup ensures that a copy in a third location is available in the event that both the primary and secondary sites fail.

You can combine UR and TC operations in a variety of ways. The following configurations are described in this appendix:

• 3DC cascade In a 3-data-center cascade configuration (3DC cascade), three data centers are used: the TC production site, the TrueCopy/Universal Replicator intermediate site, and the distant UR secondary site. The figure in the 3DC cascade configuration provides an illustration. With this configuration, you can locate the TC synchronous site near the primary site to lower I/O response time, while the UR backup provides a disaster recovery solution at a secondary site.

  For details, see 3DC cascade configuration.

• 3DC multi-target In a 3-data-center multi-target configuration (3DC multi-target), the production volume is shared by the TC and UR. This volume is the primary volume (P-VOL) for both at the primary site. The targets of each system are located at different secondary sites. They provide the TC solution and the UR asynchronous disaster recovery solution. The TC secondary site is at an intermediate location, the UR secondary site is at a distant location.

  For details, see 3DC multi-target configuration.

• Delta resync Another application of the 3DC multi-target configuration is the UR delta resync configuration, which provides a quick way to regain a long-distance copy after disaster in the event that the TrueCopy/Universal Replicator P-VOL becomes unusable. In this case, the host continues I/O operations at the intermediate TC S-VOL site. With a second UR pair previously configured between the TC S-VOL and the UR S-VOL, only differential data needs to be copied to the UR S-VOL.

  For details, see Delta resync configuration .