HP StorageWorks XP Remote Web Console Software - Manual (Page 18)

18 Overview of Continuous Access XP Journal
Figure 1 provides an overview of Continuous Access XP Journal operations.
Figure 1 Continuous Access XP Journal components for Fibre Channel connections
Journal obtain
This function stores existing primary volume data as a base-journal in the primary site journal volume.
Then this function stores write data in the journal volume every time the host updates the primary data
volume. The journal obtain operation is performed when a paircreate or pairresync operation command
is issued from the primary site. A sequence number from the host is assigned to the journal data. Using
this information, write sequence consistency at the secondary site is maintained. Update data from the
host is kept in cache. Therefore, the journal obtain function for update data is performed at a different
time than when data is received from the host or stored on the data volume.
Journal copy
This function copies data in the master journal volume at the primary site to the restore journal volume at
the secondary site. When a paircreate or pairresync operation command is issued from the primary site,
the secondary array issues the read journal command to the primary array to request a transfer of data
stored in the master journal volume. If there is journal data that should be sent, the primary array transfers
data in the journal volume to the secondary site according to the read journal command. If the primary
array does not have journal data, that information is sent. The secondary array stores journal volume data
sent from the primary site in the restore journal volume at the secondary site. Read journal commands are
issued repeatedly and regularly from the secondary site to the primary site until the journal operation
stops. After data is restored, journal sequence numbers are returned from the secondary site to the
primary site when the read journal command is issued. Based on this “remote replication complete”
information, journal data at the primary site can be safely discarded.
Journal restore
This function applies stored data in the primary site restore journal volume to the secondary data volume.
Data in the restore journal volume is restored to the secondary data volume according to write sequence
numbers. This ensures write sequence consistency between the primary and secondary data volumes.
After journal data is restored to the secondary data volume, journal data is discarded at the secondary
site.
Components
Continuous Access XP Journal operations involve local arrays at the primary and secondary sites, physical
communications paths between these arrays, and Command View XP or XP Remote Web Console.
Continuous Access XP Journal copies the original online data at the primary site to backup volumes at the