HP XP Racks - Manual (Page 75)

9 Disaster recovery
This chapter discusses disaster recovery.
Disaster recovery overview
Preparing for disaster recovery involves the following major steps:
1.
Identify the volumes and groups that contain important files and data for disaster recovery.
2. Create Continuous Access Synchronous pairs, paying special attention to the options in P-VOL
Fence Level Settings to ensure that the system responds the way you want in the event of a
failure (see
“Allowing I/O to the P-VOL after a split—Fence Level options” (page 20) ).
3. Install and configure host failover software between the local and remote sites.
4. Establish file and database recovery procedures. These procedures for recovering volumes
due to control unit failure should already be in place.
5. Make sure that the host system at the local site is configured to receive sense information from
the XP7 primary system (for example, using RAID Manager or SNMP). This should also be
done at the remote site if a host is connected to it.
NOTE: Procedures for disaster recovery involve releasing pairs. However, when using RAID
Manager you can perform disaster recovery without releasing pairs. To do this, when setting up
Continuous Access Synchronous, add remote paths between the secondary system Initiator ports
and primary system RCU Target ports. Then add a remote connection from the secondary system
CU to the primary system CU. Use the same path group ID as you used from the primary to
secondary system connection.
Remote copy and disaster recovery procedures are complex. Consult your HP account team on
sense-level settings and recovery procedures.
Sense information shared between sites
When the primary system splits a Continuous Access Synchronous pair due to an error condition,
the primary and secondary system send sense information with unit check status to the appropriate
hosts. This is used during disaster recovery to determine the consistency of the S-VOL, and must
be transferred to the remote site via the host failover software.
File and database recovery
File recovery procedures for disaster recovery should be the same as those used for recovering a
data volume that becomes inaccessible due to control unit failure.
Continuous Access Synchronous does not provide a procedure for detecting and retrieving lost
updates. To detect and recreate lost updates, you must check other current information (for example,
database log file) that was active at the primary system when the disaster occurred.
The detection and retrieval process can take some time. Your disaster recovery scenario should
be designed so that detection and retrieval of lost updates is performed after the application has
been started at the remote site.
You should prepare for file and database recovery using files for file recovery (for example,
database log files that have been verified as current).
Switching operations to the remote site
If a disaster or failure occurs at the local site, the first disaster recovery activity is to switch your
operations to the remote site. S-VOLs are recovered individually based on the pair status and P-VOL
fence level information for each pair.
Disaster recovery overview 75