Extended consistency groups – HP StorageWorks XP Remote Web Console Software User Manual
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group are also called the primary data volumes. The journal volumes in the master journal group
are called the master journal volumes. The data volumes in the restore journal group are similarly
called the secondary data volumes. The journal volumes in the restore journal group are called
the restore journal volumes.
The data update sequence from the host is managed per the journal group. The data update
sequence consistency between the master and restore journal groups to be paired is maintained
and ensured. The master and restore journal groups are managed according to the journal group
number. The journal numbers of master and restore journal groups that are paired can be different.
One data volume and one journal volume can belong to only one journal group.
CAUTION:
Data volumes and journal volumes that belong to different LDKCs cannot coexist in
the same journal group.
For detailed information about specifying journal groups, see
“Journal Group Specifications”
.
Extended Consistency Groups
To maintain data consistency while performing remote copy operations between more than one
primary storage system and more than one secondary storage system, you must register journal
groups in an extended consistency group (abbreviated as EXCTG). An extended consistency group
is a collection of journal groups. This manual uses the term primary EXCTG to refer to an extended
consistency group for the primary storage systems and uses the term secondary EXCTG to refer to
an extended consistency group for the secondary storage system.
A secondary EXCTG must be configured to maintain data consistency if you perform remote copy
operations between more than one primary and secondary storage system. Because you need to
reverse the primary and secondary sites if a failure occurs, it is recommended that a primary EXCTG
also be configured. While you can register the journal groups of up to four different storage systems
in the same extended consistency group, you cannot register one journal group in different extended
consistency groups. The following table explains specifications of extended consistency groups.
Table 3 Specifications of Extended Consistency Groups
Specifications
Item
Up to four per one-storage system
The number of extended consistency groups that can be created
Up to 16
The number of journal groups that can be registered in one extended
consistency group
The configuration of both the primary and secondary extended consistency groups (EXCTGs)
provides the following benefits:
•
Guaranteed Consistency of Data Update Sequence
Universal Replicator for Mainframe restores journal data to secondary data volumes by taking
the following steps. This procedure guarantees the consistency of the data update sequence
within an extended consistency group.
1.
Universal Replicator for Mainframe checks the extended consistency group for the time
stamps of all journal data that have not been restored to secondary data volumes, and
then identifies the latest time stamp for each journal group.
In the example shown in
, the latest time stamp for each journal group
is as follows:
◦
In journal group 1, the latest time stamp is 15:00.
◦
In journal group 2, the latest time stamp is 15:02.
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About Universal Replicator for Mainframe Operations