Considering the p-vol fence level setting – HP StorageWorks XP Remote Web Console Software User Manual
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3.
Use the appropriate combination of XP Continuous Access options for disaster recovery:
•
XP Continuous Access Asynchronous offloading timer option and Time Out (Copy Pending)
group option. The Time Out (Copy Pending) group option can be used to limit the time
duration during which updates may be lost.
The offloading timer value should be less than the HBA timeout value.
When channel-extenders are used for XP Continuous Access Async, the offloading timer
should be set to 35 seconds or less to avoid affecting host I/O performance.
•
XP Continuous Access Asynchronous Error Level pair option, and XP Continuous Access
Synchronous P-VOL Fence Level pair option (see
).
4.
Establish file and database recovery procedures. These procedures should already be
established for recovering volumes which become inaccessible due to a control unit 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 RAID 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 XP Continuous
Access pairs.
Considering the P-VOL Fence Level Setting
The P-VOL fence level setting (see
“Changing Pair Options” (page 129)
) for each XP Continuous
Access Synchronous pair determines whether the P-VOL will be fenced when XP Continuous Access
remote copy operations fail.
summarizes the effect of the fence level setting
on an XP Continuous Access Synchronous P-VOL.
The P-VOL fence level setting does not apply to XP Continuous Access Asynchronous pairs. XP
Continuous Access Asynchronous P-VOLs are never fenced due to suspension of the pair.
Table 31 Effect of the Fence Level Setting on an XP Continuous Access P-VOL
Write I/O operations to the P-VOL will be (On Each
Fence Level Setting):
Never
Status
Data
Type of Failure
Accepted
Accepted
REJECTED
The update copy operation failed, and the MCU was able to
change the status of the S-VOL to PSUE.
Accepted
REJECTED
REJECTED
The update copy operation failed, and the MCU was NOT
able to change the status of the S-VOL to PSUE.
Data. When Data is selected, the P-VOL will be fenced if an update copy operation fails. This
P-VOL fence level setting ensures that the S-VOL remains identical to the P-VOL once the XP
Continuous Access pair is synchronized, but makes the P-VOL inaccessible for updates whenever
XP Continuous Access remote copy operations fail. This setting should be considered for the most
critical volumes for disaster recovery. This setting reduces the amount of time required to analyze
the currency of the S-VOL during disaster recovery efforts. This setting is also designed for
applications that can continue to operate with another device pair.
Status. When Status is selected, the P-VOL is fenced only if the MCU is not able to change the
S-VOL pair status to PSUE. If the MCU successfully changes the S-VOL pair status to PSUE, subsequent
write I/O operations to the P-VOL will be accepted, and the MCU will keep track of updates to
the P-VOL. This allows the pair to be resynchronized quickly using the pairresync operation
(out-of-sync-tracks only). This setting also reduces the amount of time required to analyze the S-VOL
currency during disaster recovery.
Never. When Never is selected, the P-VOL is never fenced when the pair is suspended. This P-VOL
fence level setting ensures that the P-VOL remains available to applications for updates, even if all
XP Continuous Access copy operations have failed. The S-VOL may no longer be in sync with the
Using XP Continuous Access for Disaster Recovery Operations
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