HP StorageWorks XP Remote Web Console Software - Manual (Page 22)

Primary site Secondary site
Primary host Secondary host
Write instruction
Primary storage system Secondary storage system
Primary
data
volume
Issuing Read
Journal command
Journal restore
function Journal obtain
function
Journal copy function
Secondary
data
volume
Master
journal
volume
Restore
journal
volume
Figure 1 UR Components for Fibre-Channel Connection
Journal Obtain
Journal obtain is the function to store the already stored data in the primary data volume as a base-journal
in the journal volume at the primary site. And then, this function stores the write data as a journal data
in the journal volume with every update of the primary data volume according to the write instruction
from the host. The journal obtain operation is performed according to the instruction of add pair or
Resume Pair operation 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 the cache. Therefore, the journal obtain function
for the update data is performed asynchronously from the time the storage system receives the update
data from the host and stores the update data to the data volume.
Journal Copy
Journal copy is the function to copy 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 to transfer the data that is stored in the master journal volume
according to the pair create or Resume Pair operation instruction from the primary site. The primary
storage system transfers the data in the journal volume to the secondary site according to the read journal
command if it has the journal data that should be sent. If the primary storage system does not have the
journal data, the information is sent. The secondary storage system stores the journal volume data that is
sent from the primary site in the restore journal volume at the secondary site. The read journal commands
are issued repeatedly and regularly from the secondary site to the primary site until the journal operation
is stopped. After the data are restored, the journal sequence numbers are informed from the secondary
site to the primary site when the read journal command is issued. According to this information, the
journal data at the primary site are discarded.
Journal Restore
Journal restore is the function to reflect the stored data in the restore journal volume to the secondary
data volume at the secondary site. The data in the restore journal volume are restored to the secondary
data volume according to the write sequence number. This will ensure the write sequence consistency
between the primary and secondary data volumes. After the journal data are restored to the secondary
data volume, the journal data are discarded at the secondary site.
22 Overview of Universal Replicator Operations