HP StorageWorks XP Remote Web Console Software - Manual (Page 15)

Continuous Access XP Journal user guide 15
reliable data replication systems using journal volumes to reduce the chances of copy operation
suspensions. Copy operations can be suspended due to restrictions on data transfers from the primary site
to the secondary site.
Functionality
You can use Continuous Access XP Journal to create duplicate volumes by copying data from primary data
volumes in the primary disk array to secondary data volumes in the secondary disk array at the remote
location. To duplicate volumes, perform the following steps sequentially with the primary and secondary
data volumes and the journal volumes:
• Journal obtain function at the primary site
• Journal copy function between the primary and secondary sites
• Journal restore function at the secondary site
Write sequence consistency for the primary data volume at the primary site is also maintained for the
secondary data volume at the secondary site by the write sequence number assigned for the journal data
with the journal obtain function. Data integrity is maintained; concurrency is not maintained. Continuous
Access XP Journal reduces the occurrence of pair suspended status as a result of restrictions of data transfer
from the primary site to the secondary site by storing write data from the host in the master and restore
journal volumes and provides the high reliable duplication system.
Figure 1 provides an overview of Continuous Access XP Journal operations.
Figure 1 Continuous Access XP Journal components for fibre-channel connections
Journal obtain function
This function stores existing data in the primary data volume as a base-journal in the journal volume at the
primary site. Then this function stores the write data as journal data in the journal volume every time the
primary data volume is updated according to the write instruction from the host. The journal obtain
operation is performed when a paircreate or pairresync operation command is issued from the primary
site. The write sequence number from the host is assigned to the journal data. According to this
information, the write sequence consistency at the secondary site can be maintained. The update data
from the host is kept in cache. Therefore, the journal obtain function for the update data is performed at a
different time than data from the host is received or data is stored on the data volume.
Journal copy function
This function copies data in the master journal volume at the primary site to the restore journal volume at
the secondary site. The secondary disk array issues the read journal command to the primary disk array to
request a transfer of data stored in the master journal volume when a paircreate or pairresync operation