HP XP Continuous Access Software User Manual
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Figure 36 Restoring an XP Business Copy P-VOL - Step 9
XP Continuous Access Synchronous (3DC Cascading Configuration)
The XP24000/20000 Disk Array provides a function to combine XP Continuous Access Journal
and XP Continuous Access Synchronous. 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 the secondary sites are 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 when a failure occurs in
the primary site, regardless of whether the distance between the primary and the secondary sites
is short or long. These intentions will be 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.
shows an example of a 3DC cascading configuration in which XP Continuous
Access Journal and XP Continuous Access Synchronous are combined. In this configuration, the
volume in the primary site is an XP Continuous Access Synchronous primary volume (P-VOL). The
corresponding XP Continuous Access secondary volume (S-VOL) is the volume at the intermediate
site, which is a short distance from the primary site. This XP Continuous Access Synchronous
secondary volume is also used as an XP Continuous Access Journal primary data volume. The
corresponding XP Continuous Access 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 XP Continuous
Access Synchronous primary volume at the primary site, data will be transferred vian XP Continuous
Access Synchronous and XP Continuous Access Journal to the secondary site and will be restored
to the secondary data volume.
Figure 37 3DC Cascading Configuration (Combining XP Continuous Access Journal with XP
Continuous Access Synchronous)
Data that is copied by XP Continuous Access Synchronous is stored in the XP Continuous Access
Journal primary data volume. If a failure occurs in the XP Continuous Access Synchronous P-VOL,
business tasks can continue by using data in the XP Continuous Access Journal secondary data
volume containing data in the XP Continuous Access Synchronous P-VOL. Data in the XP Continuous
Access Synchronous P-VOL is restored vian XP Continuous Access Journal to the secondary data
volume at the secondary site with update sequence integrity ensured. If a failure occurs at both the
XP Continuous Access Synchronous P-VOL and S-VOL due to a disaster or some other reason,
disaster recovery can be performed using the XP Continuous Access Journal secondary data volume.
an XP Continuous Access Synchronous P-VOL must be created in a storage system. The fence level
of the XP Continuous Access Synchronous P-VOL must be Data.
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Preparing for XP Continuous Access Journal Operations