HP StorageWorks Continuous Access XP user guide for the XP10000/XP12000 (December 2005)

Continuous Access XP user guide for the XP10000/XP12000 33
disk array cache to adequately support Continuous Access XP remote copy workloads and local workload
activity.
Host failover software
Host failover software is a critical component of any disaster recovery effort. When an MCU fails to
maintain synchronization of a Continuous Access XP pair, the MCU generates sense information. This
information must be transferred to the remote site via the host failover software for effective disaster
recovery.
Duplicate volumes
Because the contents of the P-VOL and S-VOL of a Continuous Access XP pair are identical, the S-VOL is
considered a duplicate of the P-VOL. Because 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 Continuous Access XP S-VOLs so they do not auto-mount or come online to
the same host at the same time as the P-VOLs (see the following CAUTION).
Continuous Access XP does not allow the S-VOL to be online (except when the pair is split). If the S-VOL is
online, the Continuous Access XP paircreate operation fails.
CAUTION: If Continuous Access XP S-VOLs are physically attached to the same host servers as
Continuous Access XP P-VOLs, a problem might occur. When a Continuous Access XP pair is deleted, the
old S-VOL 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 Continuous Access XP S-VOLs and P-VOLs are connected to the same hosts, HP strongly recommends that
you define S-VOLs to remain offline (or create them with the RAID Manager ‘no read’ option) to avoid this
problem.
Host system crash
Contents of the P-VOL and S-VOL of a Continuous Access XP pair may become inconsistent if the host
system hangs (crashes) while a write operation is being performed on the Continuous Access XP P-VOL,
and the write operation cannot be retried because of the following reasons:
• A check condition is reported to the host due to a failure in the disk array when the write command for
the Continuous Access XP pair is issued.
• A reset command is issued from the host, and the write operation is stopped (write operation is
incomplete).
If these conditions occur, retry the job to complete the write operation.
Installing hardware
Initial installation of the Continuous Access XP hardware is performed by the user and the HP
representative. Hardware configurations for Continuous Access XP Synchronous and Continuous Access XP
Asynchronous are the same.
1. User: Identify locations of Continuous Access XP primary and secondary volumes (P-VOLs and S-VOLs),
so Performance Advisor hardware can be installed and configured properly.
NOTE: If you are using Command View XP, proceed with step 2. Otherwise, you can use XP
Remote Web Console directly to manage MCUs and RCUs.
2. User and HP representative: Install the Command View XP management station near Continuous
Access XP MCUs, and connect the Command View XP management station to MCUs via the internal
LAN. HP recommends you also install a Command View XP management station connected to RCUs at
the remote site.
3. HP representative: Ensure that MCUs and RCUs are properly configured for Continuous Access XP
operations (for example, cache or NVS) (see ”Cache and nonvolatile storage (NVS)” on page 32).