HP StorageWorks XP Remote Web Console Software - Manual (Page 37)

• Creating and storing journals at the primary storage system (see the next section),
• Copying journals to the secondary storage system
• Storing journals at the secondary storage system
• Selecting and restoring journals at the secondary storage system
• Types of journals
Creating and Storing Journals at the Primary Storage System
When a primary storage system performs an update (host-requested write I/O) on a URz primary data
volume, the primary storage system creates a journal data to be transferred to secondary storage system.
The journal data will be stored into the cache at first, and then into the journal volume.
Metadata information will be attached to journal data (see
Table 3 on page 37). When base-journal is
obtained, only metadata information is created and stored in UR cache or the journal volume.
Table 3 Metadata Information
Type Description
Journal type Type of journal (e.g., base-journal or update journal)
LDEV No. (data) The number of primary data volume that stores the original data
Original data storing position The primary data volume slot number, and the start and end of sub-block
number (data length)
LDEV No. (journal) The volume number of master journal volume that stores the journal data
Journal data storing position The slot number of master journal volume, and the start sub-block number
Journal sequence number
The sequence number that is assigned when the journal is obtained
Timestamp The time when the journal data is obtained
The journal sequence number indicates the primary data volume write sequence that the primary storage
system has created for each journal group. The journal data is transferred to the secondary storage system
asynchronously with the host I/O. The secondary storage system updates the secondary data volume in
the same order as the primary data volume according to the sequence number information in the journal.
URz processing continues uninterrupted if the SVP reboots or even if the SVP fails.
Copying Journals to the Secondary Storage System
When a primary subsystem receives a read journal command from a secondary subsystem, the primary
subsystem sends the journal data to the secondary subsystem. The secondary subsystem’s initiator ports
act as host processor channels and issue special I/O operations, called remote I/Os (RIOs), to the
primary subsystem. The RIO transfers the journal data in FBA format using a single channel command.
The primary subsystem can send several journal data using a single RIO, even if their sequence numbers
are not contiguous. Therefore, the journal data are usually sent to the secondary subsystem in a different
order than the journal data were created at the primary subsystem. The secondary subsystem ensures
that the journal data are applied to the secondary data volume in the correct sequence. This method of
remote I/O provides the most efficient use of primary subsystem-to-secondary subsystem link resources.
NOTE:
You must make sure that your channel extenders are capable of supporting remote I/O. For further
details, please contact your Hitachi account team.
Hitachi Universal Replicator for z/OS user guide for XP12000/XP10000 Disk Arrays and SVS 200 37