HP XP Continuous Access Software - Manual (Page 12)

Figure 1 XP Continuous Access Journal Operations for a Fibre Channel Connection
Journal Obtain
Journal obtain is the function that stores data from the primary data volume as a base-journal in
the primary site journal volume. The journal obtain function, with every update of the primary data
volume according to the write instruction from the host, then stores the write data as journal data
in the journal volume.
The journal obtain operation uses the pair create or pair resync instructions from the primary site.
The write sequence consistency at the secondary site is maintained using the write sequence number
assigned by the primary system to the host data that is being replicated. The update data from the
host is kept in the cache. Therefore, the receipt of the update data from the host and the storage
of data to the data volume is performed asynchronously.
Journal Copy
Journal copy is the function that copies the data in the master journal volume at the primary site
to the restore journal volume at the secondary site. The secondary storage system issues the read
journal command to the primary storage system to request the transfer of the data that is stored in
the master journal volume based on the pair create or pair resync operation instruction from the
primary site.
If it has the journal data, the primary storage system transfers the data in the journal volume to the
secondary site in response to the read journal command. If the primary storage system does not
have the journal data, it informs the secondary system.
The secondary storage system stores the journal volume data that is sent from the primary site to
the restore journal volume at the secondary site. The read journal commands are repeatedly issued
by the secondary site to the primary site until the journal operation is completed.
After the data transfer is complete, in response to the read journal command, journal sequence
numbers are returned from the secondary site to the primary site. Based upon this information,
journal data at the primary site are discarded.
Journal Restore
Journal restore is the function that reflects stored data in the restore journal volume to the secondary
data volume at the secondary site. The data in the restore journal volume is restored to the secondary
12 About XP Continuous Access Journal Operations