HP StorageWorks XP Remote Web Console Software - Manual (Page 170)

Fence Level Setting on a TrueCopy for Mainframe M-VOL” (page 170) summarizes the effect of the
fence level setting on a TrueCopy for Mainframe Synchronous M-VOL.
The M-VOL fence level setting does not apply to TrueCopy for Mainframe Asynchronous pairs. The
TrueCopy for Mainframe Asynchronous M-VOL is never fenced due to suspension of the pair.
Table 48 Effect of the Fence Level Setting on a TrueCopy for Mainframe M-VOL
Write I/O operations to the M-VOL will be (On Each Fence Level Setting):
Never
(CRIT=NO)
Status
(CRIT=YES-PATHS)
Data
(CRIT=YES-ALL)
Type of Failure
Accepted Accepted REJECTED The update copy operation
failed, and the MCU was
able to change the status of
the R-VOL to suspended.
Accepted REJECTED REJECTED The update copy operation
failed, and the MCU was
NOT able to change the
status of the R-VOL to
suspended.
Data (CRIT=YES-ALL). When this fence level setting is selected, the M-VOL will be fenced if an
update copy operation fails. This M-VOL fence level setting makes the M-VOL inaccessible to
applications for updates whenever TrueCopy for Mainframe remote copy operations fail. This
setting should be considered for the most critical volumes for disaster recovery. This setting will
reduce the amount of time required to analyze the currency of the R-VOL during disaster recovery
efforts. This setting is also designed for applications which can continue to operate with another
device pair (for example, IMS logger dual write log files).
Status (CRIT=YES-PATHS). When this fence level is selected, the M-VOL is fenced only if the MCU
is not able to change the R-VOL pair status to suspended. If the MCU successfully changes the
R-VOL pair status to suspended, subsequent write I/O operations to the M-VOL will be accepted,
and the MCU will keep track of updates to the M-VOL. This allows the pair to be resynchronized
quickly using the resync (out-of-sync-cylinders) copy operation (MODE=RESYNC). This setting will
also reduce the amount of time required to analyze the R-VOL currency during disaster recovery.
Never (CRIT=NO). When this fence level is selected, the M-VOL is never fenced when the pair is
suspended. This fence level setting ensures that the M-VOL remains available to applications for
updates, even if all TrueCopy for Mainframe copy operations have failed. The R-VOL may no
longer be in sync with the M-VOL, but the MCU will keep track of M-VOL updates while the pair
is suspended. ERC is essential if this fence level setting is used. For disaster recovery, the currency
of the R-VOL is determined by using the sense information transferred via ERC or by comparing
the R-VOL contents with other files confirmed to be current.
To exchange CRIT=Y(ALL) and CRIT=Y(PATHS), the HP disk array system option mode 36 can be
used. For further information on the HP disk array modes, see
“XP Disk Array Modes for TrueCopy
for Mainframe” (page 12) .
For further information on the CESTPAIR CRIT parameter and its two modes of operation,
CRIT(YES-PATHS) and CRIT(YES-ALL).
Transferring Sense Information Between Sites
When the MCU (or RCU for TrueCopy for Mainframe Asynchronous) suspends a TrueCopy for
Mainframe pair due to an error condition, the MCU/RCU sends sense information with unit check
status to the appropriate host(s). This sense information is used during disaster recovery to determine
the currency of the R-VOL. If the host system does not support IBM PPRC, you must transfer the
sense information to the remote site via the error reporting communications (ERC). If the host system
supports IBM PPRC and receives PPRC-compatible sense information related to a TrueCopy for
Mainframe pair, the host OS will:
170 TrueCopy for Mainframe Usage Scenarios