HP StorageWorks XP24000 Continuous Access Journal Software User and Reference Guide, v01 (T5278-96001, June 2007)

2 About C ontinuous Access Journal
Operations
Continuous Access Journal provides a RAI D storage-based hardware solution for disaster recovery which
enables fast and ac curate system recovery. Once Continuous Access Journal operations are established,
duplicate copies of data are automatically maintained for backup and disaster recovery purposes. During
normal Continuous Access Journal operations, the primary data volumes remain online to all hosts and
continue
to process both read and write I/O op erations. In the event of a d isaster or system failure, the
secondary copy of data can be rapidly invoked to allow recovery with a very high level of data integrity.
Continuous Access Journal ca n also be used for data duplication and m igration tasks.
Continuous Access Journal represents a unique and outstanding disaster recovery solution for large
amounts
of d ata which span multiple volumes. The Continuous Access Journal group-based update
sequence consistency solution enables fast and accurate database recovery, even after a rolling disaster,
without the need for time-consuming data recovery procedures. The Continuous Access Journal journal
groups (volume groups) at the secondar y site can be recovered with full update sequence consistency, but
the
updates will be behind the primary site due to the asynchronous remote copy operations.
Continuous Access Journal p rovides update sequence consistency for user-defined journal group (for
example, large databases) as well as protection for write-dependent applications in the event of a disaster.
When Continuous Access Journal is used, data to be copied will be temporarily stored in journal
volumes, which are a type of volume. Continuous Access Journal enables you to configure and manage
highly reliable data replication systems by using journal volumes to reduce the chances of suspension
of copy operation. Copy op erations can be suspended due to restrictions on data transfers from the
primary site to the secondary site.
This overview of Continuous Access Journal operations d escribes:
• Overview of Continuous Access Journal operations (see “Functionality Overview” on page 17),
• Continuous Access Journal components (see
“Continuous Access Journal Components” on page 19),
• Continuous Access Journal remote copy operations (see
“Continuous Access Journal Remote Copy Operations” on page 26),
•
Continuous Access Journal journal operations (see “Journal Processing”onpage 30),
•
Continuous Access Journal journal group operations (see “Journal Group Operations”onpage28),
•
Continuous Access Journal data volume pair status (see “Pair Status”onpage32).
Functionality Overview
Continuous Access Journal enables you to create duplicate volumes by copying data from the p rimary
data volumes in the primary storage system to the secondary data volumes in the secondary storage
system at the remote location. To perform this function, the journal obtain function at the primary site, the
jou
rnal copy function between the primary and secondary sites, and the journal restore function at the
secondary site are performed sequentially with the primary and secondar y data volumes and the journal
volumes. Write sequence consistency for the primary data volume a t the primary site is also maintained
for
thesecondarydatavolumeatthe secondarysitebythe write sequencenumberassignedfor thejournal
da
ta with the journal ob tain function, so that you can configure the d up licate system which has data
in
tegrity. The Continuous Access Journal c an reduce the occurrences of pair suspended status according
to
the
restrictions for data transfer from the primary site to the secondary site by storing the write data
f
rom the host in the master and restore journal volumes and provide a highly reliable duplication system.
F
igure 1 on page 18 shows an overview of Continuous Access Journal operations.
XP24000 Continuous Access Journal Software User a nd Reference Guide
17