You can combine GAD and Universal Replicator to create a configuration that can continue to operate in the event of a multi-site failure.
In a GAD system, the server accesses the primary and secondary sites simultaneously and shares the same data between the two sites (at campus distance). If a failure occurs at one site, you can continue operations at the other site. However, if a failure occurs at both sites, for example due to a large-scale disaster, you will not be able to continue operations with the data redundancy provided only by GAD.
To manage this situation, you can implement a 3-data-center (3DC) configuration by combining GAD and Universal Replicator (UR). This configuration is called a GAD 3DC delta resync (GAD+UR) configuration. If there is a failure at both the primary site and the GAD secondary site, the GAD+UR configuration enables you to continue operations using the UR secondary site (at metro distance).
- (VSP One Block 20 series) If a GAD pair is created by using volumes connected to a host via NVMe-oF, UR cannot be used with GAD. A 3DC delta resync configuration with GAD and UR is not supported.
- The CCI remote command device is not required in GAD+UR configurations.
- Volumes in a 3DC GAD+UR configuration cannot be shared with the following volumes:
- UR volumes in a system with multiple storage systems in the primary and secondary sites
- UR volumes in a 3DC multi-target configuration with TC and UR
- UR volumes in a 3DC multi-target configuration with 3 UR sites
- UR volumes in a 3DC cascade configuration with 3 UR sites
- 3DC delta resync configuration with GAD and UR is supported by VSP One B26, VSP One B28, and VSP E series. In this configuration, VSP One B26 and VSP One B28 can be connected with the following storage systems:
- VSP E1090
- VSP E990, VSP E790, VSP E590
The following table lists the combinations of the storage system models and the required DKCMAIN versions in a 3DC delta resync configuration with GAD and UR.
| Combination of storage system models | DKCMAIN version |
|---|---|
| VSP One B26 or VSP One B28 and VSP E590 or VSP E790 or VSP E990 or VSP E1090 | VSP One B26, VSP One B28: All versions |
| VSP E590, VSP E790, VSP E990, VSP E1090: 93-07-23 or later |
The following figure shows the required configuration for GAD+UR operations. You must use this configuration when combining GAD with UR.
In a GAD+UR configuration:
- The P-VOL of the GAD pair functions as the P-VOL of the UR pair.
- The S-VOL of the GAD pair functions as the P-VOL of the UR delta resync pair.
- The UR S-VOL has two mirror IDs, one for the UR pair, and one for the UR delta resync pair.
- The UR delta resync pair consists of the GAD S-VOL at the GAD secondary site and the UR S-VOL at the UR secondary site. This UR delta resync pair allows you to synchronize the UR pair S-VOL by using the journal data at the GAD secondary site in the event of a failure at the primary site.
- When combining GAD with UR, create the GAD pair first, and then create the UR pair. The GAD pair cannot be used with a UR pair that was created first.
A special case for using the GAD+UR configuration is to migrate the UR environment between the current primary and secondary sites to different primary and secondary sites while keeping the UR pairs.