HP StorageWorks XP Remote Web Console Software - Manual (Page 31)

The base-journal data is stored in the entire data volume or the area for the difference. The area for
the difference is used when the difference resynchronization operation is performed. The journal data
for the entire data volume is created when the data volume pair is created. The difference journal
data is obtained when the pair status of the data volume changes from the Suspending Pair resync
status to the status. Merging the difference bitmaps that are recorded on both primary and secondary
data volumes enables you to obtain the journal data for only difference. When a data volume pair is
suspended, the status of data that is updated from the host to the primary and secondary data volumes
is recorded to the difference bitmap.
The base-journal data of primary storage system is stored to the secondary storage system journal volume
according to the read command from the secondary storage system. After that, the base-journal data is
restored from the journal volume to the secondary data volume. The initial copy operation will finish
when all base-journals are restored.
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.
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.
This section describes the following journal group operation options available in URz:
• Timer type option
• Journal group operations
Timer Type Option
The timer type option allows you to specify the method applied by the primary storage system to acquire
the time-stamp information for each journal data. The following timer types are available for selection:
Hitachi Universal Replicator for z/OS user guide for XP12000/XP10000 Disk Arrays and SVS 200 31