Chapter 10 Usage Scenarios 10-3
Hitachi Universal Replicator for IBM /OS User’s Guide
File and Database Recovery Procedures
When the primary storage system (or secondary storage system for URz)
suspends a URz pair due to an error condition, the primary storage system or
secondary storage system sends sense information with unit check status to
the appropriate host(s). This sense information is used during disaster
recovery. You must transfer the sense information to the secondary site via
the error reporting communications (ERC).
Note: Make sure that the primary and secondary storage systems are
configured to report the service-level SIMs to the host.
When the primary or secondary storage system suspends a URz pair due to a
disaster, the secondary data volume may contain in-process data. A data set
could be open, or transactions may not have completed. Therefore, you need
to establish file recovery procedures. These procedures should be the same as
those used for recovering data volume that becomes inaccessible due to
control unit failure.
URz does not provide any procedure for detecting and retrieving lost updates.
To detect and recreate lost updates, you must check other current information
(e.g., database log file) that was active at the primary site when the disaster
occurred. Note that the journal log file entries of most DBMS have the same
system TOD clock information that is used for the I/O time-stamps (when
timer type = system). The URz group consistency time can be extremely
useful when performing this detection and retrieval. Since this
detection/retrieval process can take a while, your disaster recovery scenario
should be designed so that detection/retrieval of lost updates is performed
after the application has been started at the secondary site.
For details on the timer type option, see section
Timer Type Option.
You should prepare for file and database recovery by using:
• Files for file recovery (e.g., database log files which have been verified as
current).
• The sense information with system time stamp which will be transferred via
ERC.
Important: Remote copy and disaster recovery procedures are inherently
complex. Consult your Hitachi account team on sense-level settings and
recovery procedures.
Note: See section Recovering a Pinned Track on a Journal Volume for
information on recovering a pinned track on a URz volume.
