HP XP Continuous Access Software - Manual (Page 74)

Figure 28 Restoring Business Copy XP P-VOLs, step 9
Combining Continuous Access XP Journal with Continuous Access XP (3DC
cascading configuration)
The local array allows Continuous Access XP Journal and Continuous Access XP Synchronous to
be combined. This combination is intended to ensure that the response time against host I/Os is
comparable, regardless of whether the distance between the primary and secondary sites is short or
long. This combination is also intended to ensure that the secondary site stores data that has been stored
in the primary site even if a failure occurs in the primary site. These intentions are fulfilled if remote copy
operations are performed using cascading connections and a three data center (3DC) configuration. In a
3DC configuration, an intermediate site is located between the primary and secondary sites.
Figure 29 shows an example of a 3DC cascading configuration in which Continuous Access XP Journal
and Continuous Access XP Synchronous are combined. In this configuration, the volume in the primary
site is a Continuous Access XP Synchronous primary volume (P-VOL). The corresponding Continuous
Access XP secondary volume (S-VOL) is the volume in the intermediate site, which is a short distance from
the primary site. This Continuous Access XP Synchronous secondary volume is also used as a Continuous
Access XP Journal primary data volume. The corresponding Continuous Access XP Journal secondary
data volume is the volume in the secondary site, which is a long distance from the intermediate site. If a
host issues an I/O to the Continuous Access XP Synchronous primary volume in the primary site, data is
transferred using Continuous Access XP Synchronous and Continuous Access XP Journal to the secondary
site and is restored to the secondary data volume.
Figure 29 3DC cascading configuration (combining CA XP Jour. with CA XP Sync.)
Data that Continuous Access XP Synchronous copies is stored in the Continuous Access XP Journal
primary data volume. If a failure occurs at the Continuous Access XP Synchronous P-VOL, you can
continue your business tasks using data in the Continuous Access XP Journal secondary data volume,
which contains data in the Continuous Access XP Synchronous P-VOL. Data in the Continuous Access XP
Synchronous P-VOL is restored through Continuous Access XP Journal to the secondary data volume in
the secondary site, with update sequence integrity ensured. If a failure occurs at both the Continuous
Access XP Synchronous P-VOL and S-VOL due to a disaster or any other reason, you can perform disaster
recovery using the Continuous Access XP Journal secondary data volume.
NOTE:
You must create a Continuous Access XP Synchronous P-VOL in a local array. The Continuous Access XP
Synchronous P-VOL's fence level must be Data.
74 Continuous Access XP Journal operations requirements and restrictions