HP XP7 Storage - Manual (Page 126)

•
3DC cascade is not supported for multiple primary and secondary systems. The Cnt Ac-J or
Cnt Ac-S pair in this configuration would be suspended when the status became PAIR or COPY.
•
The response time for host I/Os will be the response time for Cnt Ac-S operation plus the
creation time of journal data in the intermediate site.
•
The utilization rate on the local site with a 3DC cascade configuration is higher than if Cnt
Ac-J and a Cnt Ac-S systems are used independently.
Procedure for setting up 3DC cascade
Procedure 38 To set up a 3DC cascade configuration
1. Install and set up Cnt Ac-S and Cnt Ac-J on the required systems.
2. Create the Cnt Ac-S pair on the primary system. See HP XP7 Continuous Access Synchronous
User Guide for instructions.
3. When Cnt Ac-S pair status is PAIR, create the Cnt Ac-J pair on the secondary system using the
Cnt Ac-S S-VOL as the Cnt Ac-J P-VOL. The Cnt Ac-J operation is rejected by the system if Cnt
Ac-S pair status is not already PAIR.
Mirror ID must be set between 1 and 3.
3DC multi-target configuration
In a multi-target configuration, data is copied from the local site to two remote sites.As illustrated
below, the P-VOL is paired with the Cnt Ac-S secondary volume and the Cnt Ac-J S-VOL at separate
remote sites in a 3DC multi-target configuration. The Cnt Ac-S site is at an intermediate distance;
the Cnt Ac-J site is located at a greater distance.
Figure 17 3-data-center multi-target configuration
The host issues an update to the production volume and, synchronously, to the Cnt Ac-S S-VOL. As
with a standalone Cnt Ac-J system, the update data is asynchronously written from the primary
volume (P-VOL) to the Cnt Ac-J S-VOL.
The benefit of this configuration is that it provides a third copy of the data, helping to ensure that
business can continue in the event of a failure at the other two sites.
Failure recovery occurs as follows:
•
If a failure occurs in the P-VOL, business is resumed using the Cnt Ac-S S-VOL. When the failure
is corrected at the local site, business tasks are transferred back to the local site.
In addition, a quick disaster recovery solution can be put in place while the local site is being
restored, using a Cnt Ac-J pair for delta resync. In this configuration, the Cnt Ac-S S-VOL is
126 Configurations with Continuous Access Synchronous