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2-4 Chapter 3 Preparing for Universal Replicator z/OS Operations
Hitachi Universal Replicator for IBM /OS User’s Guide
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.
Components
URz operations involve the USP V storage systems at the primary and
secondary sites, the physical communications paths between these storage
systems, and the USP V URz remote console software. URz copies the original
online data at the primary site to the offline backup volumes at the secondary
site via the dedicated fibre-channel remote copy connections using a journal
volume. You can operate the URz software with the user-friendly GUI
environment using the USP V URz remote console software.
Note: Host failover software is required for effective disaster recovery with URz.
For management of URz journal groups that consist of journal volumes located
in multiple storage systems, host I/O time stamping function (provided by
MVS DFSMSdfp) is a requisite functional item. An error reporting
communications (ERC) feature is essential for URz to be able to recover data
lost in a disaster.
Figure 2-2 shows the URz components and their functions: