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3-12 Chapter 3 Preparing for Universal Replicator z/OS Operations
Hitachi Universal Replicator for IBM /OS User’s Guide
Accessing URz Primary Data Volume and Secondary Data
Volume
To ensure maximum data integrity during normal URz operations, the
secondary storage system rejects all the read/write operations issued by a
host to a URz secondary data volume. If you need write operation to a URz
secondary data volume, you must set the secondary data volume write option
(see section
Secondary Data Volume Write Option). When you resume
(Resume Pair) the split pair, the secondary storage system will send the
secondary data volume track bitmap to the primary storage system to ensure
proper resynchronization of the pair.
Cache and Nonvolatile Storage (NVS)
Cache and nonvolatile storage (NVS) must be operable for both the primary
storage system and secondary storage system of a URz data volume pair. If
not, the URz add pair operation will fail. The remote storage system cache
should be configured to adequately support not only the local workloads but
also the URz remote copy workloads.
Duplicate Volumes
Since the contents of the primary data volume and secondary data volume of
a URz pair are identical, the secondary data volume can be considered a
duplicate of the primary data volume. Since the host operating system does
not allow duplicate volumes, the host system administrator must take
precautions to prevent system problems related to duplicate volumes. You
must define the URz secondary data volume so they do not auto-mount or
come online to the same host at the same time as the primary data volume
(see
WARNING below).
URz does not allow the secondary data volume to be online (except while the
pair is split). If the secondary data volume is online, the URz add pair
operation will fail.
WARNING: If the URz secondary data volumes are physically attached to the same host
server(s) as the URz primary data volumes, the following problem can occur:
When a URz pair is released, the old secondary data volume is usually
offline. If the host is then restarted, the system administrator may be offered
both volumes and asked which volume should be left offline. This can be
confusing and is prone to error.
If the URz secondary data volumes and primary data volumes are connected to the same
host(s), Hitachi strongly recommends that the secondary data volumes are defined to
remain offline to avoid this problem.