HP StorageWorks XP Remote Web Console Software - Manual (Page 56)

Basic Behavior
This section explains the basic behavior of URz under the following conditions:
•
There are two primary subsystems and two secondary subsystems.
•
The status of all the URz pairs that use journal groups in the extended consistency group is
Duplex.
•
The primary host issues write requests to URz primary data volumes.
The following figure illustrates a URz operation when the above conditions are satisfied.
Figure 16 A URz Operation When Two Primary Subsystems and Two Secondary Subsystems are
Used
The numbers in Figure 16 (page 56) indicate the order that the processing is performed, and
correspond to the numbers in the numbered procedure below:
1. The primary host issues write requests to primary subsystems. Time stamps are added to the
data to be written.
2. The primary subsystems receive the write requests, and then notify the primary host that primary
data volumes are updated.
3. The URz journal obtain function stores data updated in primary data volumes to master journal
volumes as journal data. Time stamp information added by the primary host will be added to
journal data. Also, sequence numbers indicating the order of writing will be added to journal
data.
4. The URz journal copy function copies journal data from the master journal volumes to the
corresponding restore journal volumes. This journal copy operation will be performed
asynchronously with the journal obtain operation.
5. The secondary subsystem 1 (that is, the supervisor DKC) performs arbitration processing. In
other words, the secondary subsystem 1 restores journal data of the secondary subsystems 1
and 2, based on the time stamps and the sequence numbers added to the journal data, so
that consistency with the primary data volume is maintained.
The flow of the arbitration processing is as follows:
1. The supervisor DKC compares the time stamps, and then selects the oldest time stamp.
2. The supervisor DKC requests the subordinate DKCs to restore the journal data that has the
selected time stamp.
3. From journal data having the time stamp and earlier time stamps, the subordinate DKCs restore
all journal data that have not been restored, in the order of the sequence numbers.
56 Requirements and Restrictions for Universal Replicator z/OS Operations