HP XP Continuous Access Software - Manual (Page 50)

about the case when the system option mode 707 is set to ON, see “XP Continuous Access
Synchronous (2DC Configuration)” (page 100) .
If the system option mode 767 is set to ON when you registered the journal group, the mode 767
setting is always applied even if you change the option mode to OFF afterward. For information
about the case when the system option mode 767 is set to ON, see
“ 3DC Multi-target Configuration
of Three XP Continuous Access Journal Sites” (page 60) or “3DC Cascading Configuration of
Three XP Continuous Access Journal Sites” (page 65) .
Accessing XP Continuous Access Journal Primary Data Volumes and Secondary Data
Volumes
To ensure maximum data integrity during normal XP Continuous Access Journal operations, the
secondary storage system rejects all write operations issued by a host to an XP Continuous Access
Journal secondary data volume. If you need a write operation to an XP Continuous Access Journal
secondary data volume, you must set the secondary data volume write option (see
“Secondary
Data Volume Write Option” (page 24) ). When you resume (Pairresync) the split pair, the secondary
storage system sends 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 an XP Continuous Access Journal data volume pair. If not, the XP
Continuous Access Journal paircreate operation fails. The remote storage system cache should be
configured to adequately support the XP Continuous Access Journal remote copy workloads, as
well as any local workload activity.
When pair status is COPY, neither cache nor shared memory can be added to or removed from
the storage system. When either of these tasks is to be performed, first split any pairs in COPY
status, then resynchronize when the cache or shared memory operation is completed.
Host Failover Software
The Remote Web Console software product does not provide any host failover functions for disaster
recovery. Host failover software is a critical component of any disaster recovery effort. When a
primary storage system fails to maintain synchronization of an XP Continuous Access Journal pair,
the primary storage system generates sense information. It is very important that this information
be transferred to the remote site via the host failover software for effective disaster recovery.
Duplicate Volumes
Since the contents of the primary data volume and secondary data volume of an XP Continuous
Access Journal 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 XP Continuous Access Journal secondary data volume so it does not
auto-mount or come online on the same host at the same time as the primary data volume (see
WARNING).
XP Continuous Access Journal does not allow the secondary data volume to be online (except while
the pair is split). If the secondary data volume is online, the XP Continuous Access Journal paircreate
operation fails.
WARNING: If the XP Continuous Access Journal secondary data volumes are physically attached
to the same host server(s) as the XP Continuous Access Journal primary data volumes, the following
problem can occur:
•
When an XP Continuous Access Journal pair is released, the old secondary data volume is
usually offline. If the host is then restarted, the system administrator may be offered both
50 Preparing for XP Continuous Access Journal Operations