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2-20 Chapter 3 Preparing for Universal Replicator z/OS Operations
Hitachi Universal Replicator for IBM /OS User’s Guide
Note: If you manipulate volumes (not journal groups) to create or
resynchronize two or more data volume pairs within the same journal group,
the base journal of one of the pairs will be stored in the restore journal volume,
and then the base journal of another pair will be stored in the restore journal
volume. Therefore, the operation for restoring the latter base journal will be
delayed.
Note: You can specify None as the copy mode for initial copy operations. If the
None mode is selected, initial copy operations will not be performed. The
None mode must be used at your responsibility only when you are sure that
data in the primary data volume is completely the same as data in the
secondary data volumes.
Update Copy Operation
When a host performs a write I/O operation to a primary data volume of a
data volume pair, an update copy operation will be performed. During an
update copy operation, the update data that is written to the primary data
volume is obtained as an update journal. The update journal will be copied to
the secondary storage system, and then restored to the secondary data
volume.
The primary storage system obtains update data that the host writes to the
primary data volume as update journals. Update journals will be stored in
journal volumes in the journal group that the primary data volume belongs to.
When the secondary storage system issues "read journal" commands, update
journals will be copied from the primary storage system to the secondary
storage system asynchronously with completion of write I/Os by the host.
Update journals that are copied to the secondary storage system will be stored
in journal volumes in the journal group that the secondary data volume
belongs to. The secondary storage system will restore the update journals to
the secondary data volumes in the order write I/Os are made, so that the
secondary data volumes will be updated just like the primary data volumes are
updated.
Journal Group Operations
URz journal groups enable update sequence consistency to be maintained
across a journal group of volumes. The primary data volumes and secondary
data volumes of the pairs in a journal group must be located within one
physical primary storage system and one physical secondary storage system
(1-to-1 requirement).
When more than one data volume is updated, the order that the data volumes
are updated is managed within the journal group that the data volumes belong
to. Consistency in data updates is maintained among paired journal groups.
URz uses journal groups to maintain data consistency among data volumes.