HP XP P9500 Storage - Manual (Page 132)

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Differential data is used to resynchronize a suspended Continuous Access Synchronous or
Continuous Access Journal pair.
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When the Continuous Access Synchronous pair is recovered, the Continuous Access Journal
pair in PAIR or COPY status is automatically split by the system.
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The fence level of the Continuous Access Synchronous P-VOL must be Data.
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3DC Cascade is not supported for multiple primary and secondary systems.
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The response time for host I/Os will be the response time for Continuous Access Synchronous
operation plus the creation time of journal data in the intermediate site.
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The utilization rate on the primary site with a 3DC cascading configuration is higher than if
Continuous Access Journal and a Continuous Access Synchronous systems are used
independently.
Procedure for setting up 3DC cascade
To set up a 3DC cascading configuration
1. Install and setup Continuous Access Synchronous and Continuous Access Journal on the
required systems.
2. Create the Continuous Access Synchronous pair on the primary system. See HP P9000
Continuous Access Synchronous User Guide.
3. When Continuous Access Synchronous pair status is PAIR, create the Continuous Access
Journal pair on the secondary system using the Continuous Access Synchronous S-VOL as the
Continuous Access Journal P-VOL. Mirror ID must be set between 1 and 3.
NOTE: You must ensure that the Continuous Access Synchronous pair status changes to PAIR
before the Continuous Access Journal pair status changes to PAIR. If you have made a request for
changing the Continuous Access Journal pair status to PAIR before the Continuous Access
Synchronous pair status changes to PAIR, the request is rejected.
3DC multitarget configuration
As illustrated below, the P-VOL is paired with the Continuous Access Synchronous secondary volume
(S-VOL) and the Continuous Access Journal S-VOL at separate remote sites in a 3DC multitarget
configuration. The Continuous Access Synchronous site is at an intermediate distance; the Continuous
Access Journal site is located at a greater distance.
Figure 20 3DC multitarget
The host issues an update to the production volume and, synchronously, to the Continuous Access
Synchronous S-VOL. As with a standalone Continuous Access Journal system, the update data is
asynchronously written from the primary volume (P-VOL) to the Continuous Access Journal S-VOL.
The benefit of this configuration is that it provides a third copy of the data, helping to insure that
business can continue in the event of a failure at the other two sites.
132 Continuous Access Journal configurations with Continuous Access Synchronous