HP StorageWorks XP Remote Web Console Software - Manual (Page 86)

Figure 39 3DC Multi-Target Configuration (Combining XP Continuous Access Journal with XP
Continuous Access Synchronous)
In this configuration, the primary volume at the primary site is paired with the secondary volume
for XP Continuous Access Synchronous. This primary volume is also paired with the secondary
volume for XP Continuous Access Journal. If a host at the primary site writes data to the primary
volume, the data will be written to the XP Continuous Access Synchronous secondary volume in
real time, synchronously with writing from the host. The data will also be written to the XP Continuous
Access Journal secondary data volume, asynchronously with writing from the host. Update sequence
consistency will be maintained with the XP Continuous Access Journal secondary data volume.
In addition, you can create the XP Continuous Access Journal pair for the delta resync operation
in the 3DC muti-target configuration by specifying XP Continuous Access Synchronous S-VOL in
the XP Continuous Access Synchronous secondary site as the XP Continuous Access Journal primary
data volume, and by specifying the volume in the XP Continuous Access Journal secondary site as
the XP Continuous Access Journal secondary data volume. If you create the XP Continuous Access
Journal pair for the delta resync operation, you can resynchronize the XP Continuous Access Journal
pair by using journal data in the XP Continuous Access Synchronous secondary site when a failure
occurs in the primary site.
To perform the normal delta resync operation, a certain amount of data must be updated on the
XP Continuous Access Synchronous primary site. However, the delta resync operation that uses
remote command devices can be performed even if there is only a small amount of data to be
updated on the XP Continuous Access Synchronous primary site. Therefore, even if a disaster occurs
right after starting business tasks and only a small amount of data needs to be updated, the delta
resync operation remote command devices can be performed. If you use the delta resync function
to resume business tasks as part of recovering from disasters or failures, you must use the delta
resync function that uses remote command devices.
For detailed information about the hardware configuration required for a 3DC multi-target
configuration, see
“Hardware Configuration” (page 87) . For detailed information about the
requirements to create an XP Continuous Access Journal pair for the delta resync operation, see
“Requirements for Creating an XP Continuous Access Journal Pair for the Delta Resync Operation”
(page 89)
. For the requirements to perform the delta resync operation, see “Requirements for
Performing the Delta Resync Operation” (page 89) . For detailed information about the requirements
to create the delta resync operation environment to support remote command devices, see
“Configuring Delta Resync Operation Environment that uses Remote Command Devices” (page 91) .
If a failure occurs in an XP Continuous Access Synchronous primary volume that is also used as
an XP Continuous Access Journal primary data volume, you can resume the business tasks by using
the XP Continuous Access Synchronous secondary volume. After you resume the business tasks,
you need to remove the failure from the primary volume and transfer the business tasks back to
the primary site. For detailed information, see
“Recovering from Primary Site Disaster in a 3DC
86 Preparing for XP Continuous Access Journal Operations