HP StorageWorks XP24000 Continuous Access Software User and Reference Guide, v01 (T5278-96002, June 2007)

6Usage Scenarios
Using Continuous Access for Disaster Recovery Operations
The type of disaster and the status of the Continuous Access pairs will determine the best approach
for disaster recovery. For example, if all Continuous Access pairs are in the PAIR state when a total
system failureoccursatasingle pointintime, theS-VOLsare currentand recovery is straightforward.
Unfortunately, some disasters are not so orderly and involve intermit tent or gradual failures occurring over
a
longer period of time. The user should anticipate and plan for all types of failures and d isasters.
The major steps in preparing for disaster recovery are:
1. I dentify the volumes and groups which contain important files and data for disaster recovery. In
addition to supporting Continuous Access remote copy operations as well as RAID Manager
commands, the storage system provides batter y-backed nonvolatile duplexed cache, full
hardware redundancy, dynamic sparing, and an advanced RA I D-5 implementation to ensure full
data
integrity in the event of a sudden power outage or other failure.
2. Install the Remote Web Console computer and Continuous Access hardware and software,
and
establish Continuous Access operations for the volumes and groups identified in
step (1) . Make sure to select the proper CUs/ports to access the desired volumes. See
“Preparing for Continuous Access Operations” on page 43 for Continuous Access installation
instructions. See “Performing Continuous Access Configuration Operations”onpage69
for instructions on performing Continuous Access con fi guration o p erations. See
“Performing Continuous Access Pair Operations” on p age 99 for instructions on performing
Continuous Access pair o perations.
3. Use the appropriate combination of Continuous Access options for disaster recovery:
• Continuous Access Asynchronous offloading timer option and Time Out (Copy
Pending) group option (see “Adding Consistency Groups” on page 85 and
“Changing the Consistency Group Options” on page 86). The Time O ut (Copy Pend ing)
group option can be used to limit the time duration during which updates may be lost.
Note: The offloading timer value shou ld be less than the HBA tim eout value.
Note: When channel-extenders are used for Continuous Access Async, the offloading timer
should be
set to 35 seconds or less to avoid affecting host I/O performance.
• Continuous Access Asynchronous Error Level pair option, and Continuous Access
Synchronous P-VOL Fence Level pair option (see “Pair Options” on page 110).
4. Establish file and database recovery procedures. These procedures should already be
established for recovering volumes which become inaccessible due to a control u nit failure.
5. Make sure that the host system at the primary site is configured to receive sense information from
the
storage system MCUs (for example, via RA ID Manager or SNMP).
6. Install and configure host failover software between the main and remote sites. Host failover
capability is essential if you use the fence level setting of Status or Never for any Continuous
Access pairs.
Considering the P-VOL Fence Level Setting
TheP-VOL fencelevel setting(see“Changing Pair Options” on page 110) for e ach Continuous Access
Synchronous pair determines whether the P-VOL will be fenced when Continuous Access remote copy
o
perations fail. Table 2 3 on page 128 summarizes the effect of the fence level setting on a Continuous
Access Synchronous P-VOL.
Note: The P-VOL fence level set ting does not apply to Continuous Access Asynchronous pairs. Continuous
Access Asynchronous P-VOLs are never fenced due to suspension of the pair.
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