Truecopy asynchronous consistency group operations, Group options, Group consistency time – HP StorageWorks XP Remote Web Console Software User Manual
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TrueCopy Asynchronous Consistency Group Operations
TC390A consistency groups enable update sequence consistency to be maintained across a group of
volumes. The R-VOLs of the pairs in a consistency group must be located within one RCU (n-to-1
requirement). The TC390A consistency group operations include the following:
•
Group options
•
Group consistency time
•
Group operations
Only TCzA pairs that belong to the same CLPR can be allocated to one consistency group.
Group Options
TC390A provides the following options for each consistency group: Timer Type, Time Out [Copy Pending],
and Time Out [RCU Ready]. These options are selected when you add a group. If you want to change the
timeout options of a group, you must suspend all pairs in the group first. If you want to change the timer
type option, you must delete all pairs. The Timer Type and Time Out [Copy Pending] options must be the
same for all MCUs that contain M-VOLs in the group. The Time Out [RCU Ready] option can be different at
each MCU if necessary.
Timer Type. This group option determines how the MCU will acquire the time-stamp for the TC390A
recordsets:
•
System. When the System timer option is selected, the MCU acquires the time-stamp information for
each recordset as follows. When a TC390A pair is established, the MCU reports state-change-interrupt
(SCI) to all hosts. The host then issues a series of sense group commands to determine the device status
change and the MCU returns the same response as if the device had been added to an XRC session to
activate I/O time-stamping for the device. After 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 TC390A 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 TC390A copy
operations. For instructions on selecting the correct Time Out [Copy Pending] setting for your operational
environment, see ”
Adding Consistency Groups (Add CT Group)
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 TC390A volume pairs.
Group Consistency Time
During normal TC390A 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 TC390A R-VOL pair status (also displayed by the CQUERY TSO command to the R-VOL). As the
main system continues to update the TC390A 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 that take place during this time may be lost when a disaster occurs.