HP StorageWorks XP Remote Web Console Software - Manual (Page 30)

system to maintain update consistency of the Universal Replicator for Mainframe secondary data
volumes. Universal Replicator for Mainframe journal processing includes:
•
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
Journal Processing at the Primary Storage System
When a primary storage system performs an update (host-requested write I/O) on a Universal
Replicator for Mainframe 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 the journal data (see Table 4 (page 30) ). When
base-journal is obtained, only metadata information is created and stored in Universal Replicator
for Mainframe cache or the journal volume.
Table 4 Metadata Information
Description Type
Type of journal (for example, base-journal or update journal) Journal type
The number of the primary data volume that stores the original data LDEV No. (data)
The primary data volume slot number, and the start and end of the
sub-block number (data length) Original data storing position
The volume number of the master journal volume that stores the journal
data LDEV No. (journal)
The slot number of master journal volume, and the start sub-block number Journal data storing position
The sequence number that is assigned when the journal is obtained Journal sequence number
The time when the journal data is obtained Timestamp
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.
NOTE: Universal Replicator for Mainframe processing continues uninterrupted if the SVP reboots
or even if the SVP fails.
Types of Journal
In addition to the journal data for updating, the primary storage system sends control information
to the secondary storage system. This control information indicates when volume pair status changes
and when a primary storage system power-off sequence is initiated, and also maintains sequence
numbers in periods of low host activities.
Journal Processing at the Secondary Storage System
When a primary storage system receives a read journal command from a secondary storage
system, the primary storage system sends the journal data to the secondary storage system. The
secondary storage system’s initiator ports act as host processor channels and issue special I/O
operations, called remote I/Os (RIOs), to the primary storage system. The RIO transfers the journal
30 About Universal Replicator for Mainframe Operations