HP XP Continuous Access Software - Manual (Page 19)

2 Overview of Continuous Access
XP Journal
Continuous Access XP Journal provides a RAID storage-based hardware solution for disaster recovery that
enables fast and accurate system recovery. After establishing Continuous Access XP Journal operations,
duplicate copies of data are automatically maintained for backup and disaster recovery purposes. During
normal Continuous Access XP Journal operations, primary data volumes remain online to all hosts and
continue processing read and write I/O operations. If a disaster or system failure occurs, you can rapidly
invoke the secondary copy of the data to allow recovery with a very high level of data integrity. You can
also use Continuous Access XP Journal for data duplication and migration tasks.
Continuous Access XP Journal represents a unique and outstanding disaster recovery solution for large
amounts of data spanning multiple volumes. Continuous Access XP Journal's group-based, update
sequence consistency solution enables fast and accurate database recovery, even after a “rolling”
metropolitan area disaster, without requiring time-consuming data recovery procedures. You can recover
Continuous Access XP Journal's journal groups (volume groups) at the out of region site with full update
sequence consistency, but updates may be chronologically behind the primary site due to the nature of
asynchronous remote copy operations.
Continuous Access XP Journal provides update sequence consistency for user-defined journal groups (for
example, large databases) and protection for write-dependent applications if a disaster occurs.
When using Continuous Access XP Journal, data being copied is temporarily stored in journal volumes,
which are a type of logical volume. You can use Continuous Access XP to configure and manage
highly reliable data replication systems using journal volumes to reduce the chances of copy operation
suspensions. Copy operations can be suspended due to restrictions on data transfers from the primary
site to the secondary site.
Overview of functionality
You can use Continuous Access XP Journal to create duplicate volumes by copying data from primary
data volumes in the primary array to secondary data volumes in the secondary array at a remote
location. To duplicate volumes, perform the following steps sequentially with the primary and secondary
data volumes and journal volumes:
• Journal obtain function at the primary site
• Journal copy function between the primary and secondary sites
• Journal restore function at the secondary site
Write sequence consistency is maintained at the remote secondary site by way of a write sequence
number assigned to the journal data. Continuous Access XP Journal reduces occurrences of pair
suspended status as a result of the superior link outage tolerance provided by disk based journal volumes
for “yet to be sent” data.
Figure 1 provides an overview of Continuous Access XP Journal operations.
Continuous Access XP Journal user guide 19