HP StorageWorks XP Remote Web Console Software - Manual (Page 32)

the same response as if the device had been added to an XRC session to activate I/O
time-stamping for the device. Once I/O time-stamping is activated, the MVS IOS routine
attaches the time-stamp information (contents of time-of-day (TOD) clock) to each write I/O
operation for the device. The time-stamp indicates the time that the update was generated
during start subchannel (SSCH) at the main host system, and the time-stamp is transferred to
the MCU at the beginning of each I/O operation.
•
Local. The Local timer option enables the MCU to generate the time-stamp for each update
I/O using its own internal clock, rather than using the SMS I/O time-stamp.
•
None. The None timer option should only be selected when establishing TrueCopy for
Mainframe Asynchronous pairs in the reverse direction (from secondary to primary). When
the None option is selected, the MCU still acquires the time-stamp information from the host
I/O time-stamping function.
Time Out [Copy Pending]. This group option specifies the maximum delay allowed for TrueCopy
for Mainframe Asynchronous copy operations.
CAUTION: See “Adding Consistency Groups” (page 118) for instructions on selecting the correct
Time Out [Copy Pending] setting for your operational environment.
The RCU will suspend all R-VOLs in the group when:
•
The RCU has not had any communication from the MCU within the specified time. This situation
could indicate a disaster or failure at the primary site.
•
The RCU has been receiving recordsets from the MCU(s) but has not been able to settle a
recordset within the specified time. This situation may indicate that the RCU does not have
enough resources to handle the remote copy and I/O workloads.
RCU Ready. This option specifies the maximum delay for re-establishing MCU-RCU communications
following MCU power-off. During MCU power-on, the MCU re-establishes communication with all
registered RCUs. If it is not able to re-establish communication with an RCU within the specified
time, the MCU suspends all affected TrueCopy for Mainframe Asynchronous pairs.
Group Consistency Time
During normal TrueCopy for Mainframe Asynchronous operations, the consistency time (C/T) of
a group corresponds to the time-stamp value of the most recently settled recordset at the RCU. The
consistency time for the group is indicated as part of the TrueCopy for Mainframe Asynchronous
R-VOL pair status (also displayed by the CQUERY TSO command to the R-VOL). As the main system
continues to update the TrueCopy for Mainframe Asynchronous M-VOLs, the difference between
the current system time and the group consistency time indicates the amount of time that the R-VOLs
are behind the M-VOLs. The M-VOL updates which take place during this time may be lost when
a disaster occurs.
When a TrueCopy for Mainframe Asynchronous pair is suspended, the C/T of the suspended
R-VOL is frozen. If the RCU can ensure the update sequence consistency between the suspended
R-VOL and the other R-VOLs in the consistency group, the R-VOL C/T is frozen at the latest
consistency time of the group. Otherwise, the R-VOL C/T is frozen at the time-stamp value of the
most recent update that was successfully copied to the R-VOL. The C/T of a suspended R-VOL may
be older than the C/T of other R-VOLs in the group, and if the entire group was not also suspended,
the consistency time of the group is still ticking. For suspended TrueCopy for Mainframe
Asynchronous R-VOLs, the TrueCopy for Mainframe Detailed Information dialog box displays
whether the C/T was frozen to the group or R-VOL time.
Once you have established TrueCopy for Mainframe Asynchronous operations, you should monitor
the consistency time of each group at the RCU(s). If the average delay is longer than your disaster
recovery design can accept, you should consider adding remote copy resources (for example,
paths, cache) and/or reducing the I/O workload to improve storage system performance. If the
delay between the M-VOL update and the corresponding R-VOL update reaches the time specified
32 About TrueCopy for Mainframe Operations