HP XP P9500 Storage - Manual (Page 74)

9 Planning and procedures for disaster recovery
This chapter provides instructions for using Continuous Access Synchronous Z for disaster recovery.
Disaster recovery overview
The major steps in preparing for disaster recovery follow:
1.
Identify the volumes and groups that contain important files and data for disaster recovery.
2. Create Continuous Access Synchronous Z pairs, paying special attention to the options in
M-VOL Fence Level Settings to ensure that the system responds the way you want in the event
of a failure (see prerequisites in
“Create pairs” (page 55) ).
3. Install and configure host failover software between the main 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 main site is configured to receive sense information from
the P9500 main system. This should also be done at the remote site if a host is connected to
it.
Remote copy and disaster recovery procedures are inherently complex. Consult your HP account
team on sense-level settings and recovery procedures.
Transfer sense information between sites
When the main system suspends a Continuous Access Synchronous Z pair due to an error condition,
the main and remote system send sense information with unit check status to the appropriate host(s).
This is used during disaster recovery to determine the currency of the R-VOL, and must be transferred
to the remote site via the host failover software.
If the host system supports IBM PPRC and receives PPRC compatible sense information related to
a Continuous Access Synchronous Z pair, the host OS will:
1.
Temporarily suspend all application I/O operations to the M-VOL.
2. Enter an IEA491E message in the system log (SYSLOG) that indicates the time that the M-VOL
was suspended. Make sure that the system log is common to both the main and remote
operating systems.
3. Place specific information about the failure (SIM) in the SYS1.LOGREC dataset for use by
service personnel.
4. Wait for the IEA491E message to reach the remote system.
5. Resume all host application I/O operations to the M-VOL. If the M-VOL fence level setting
does not allow subsequent updates, the MCU will return a unit check for all subsequent write
I/O operations, and the application will terminate.
Make sure that the MCUs and RCUs are configured to report the service level SIMs to the host.
Select the Service SIM of Remote Copy = Report setting on the RCU Option dialog box.
File and database recovery
File recovery procedures are necessary in such cases. These procedures should be the same as
those used for recovering a data volume that becomes inaccessible due to control unit failure.
Continuous Access Synchronous Z 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 main 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.
74 Planning and procedures for disaster recovery