HP StorageWorks XP Remote Web Console Software - Manual (Page 36)

by the user, the MCU and RCU ensure synchronization by either completing or discarding any
pending update copy operations according to the user-specified drain/purge suspend option.
A TrueCopy for Mainframe pair is suspended by the MCU when the following suspension conditions
are detected. A TrueCopy for Mainframe Asynchronous pair can also be suspended by the RCU.
•
When the MCU detects that the user has released the pair from the RCU (for example, to
access an R-VOL at the remote site)
•
When the MCU detects an error condition related to the RCU, R-VOL, a TrueCopy for
Mainframe Synchronous update copy operation or a TrueCopy for Mainframe Asynchronous
recordset operation
•
When the RCU cannot execute DFW (DASD fast write) to the R-VOL (only if DFW required is
selected)
•
When the MCU is unable to communicate with the RCU
If a TrueCopy for Mainframe Synchronous update copy operation fails, the MCU maintains exact
synchronization by reporting a unit check and decommitting the M-VOL update, so that the host
system and application program regard that write operation to the M-VOL as failed.
When a TrueCopy for Mainframe pair is suspended, the MCU stops performing update copy
operations to the R-VOL. For a suspended TrueCopy for Mainframe Synchronous pair, the MCU
may or may not continue accepting write I/Os for the M-VOL depending on the M-VOL fence level
and suspend option (if user-requested). If the MCU accepts write I/Os for a suspended M-VOL,
the MCU records the data in the M-VOL tracks that are updated while the pair is suspended as
the differential data. For a suspended TrueCopy for Mainframe Asynchronous pair, the MCU and
RCU keep track of any recordsets that were discarded during suspension, and the MCU continues
accepting write I/Os for the M-VOL and records the data in the M-VOL tracks that are updated
while the pair is suspended as the differential data.
A suspended TrueCopy for Mainframe Asynchronous R-VOL has an additional status called the
consistency status which is displayed only at the RCU. The consistency status of a suspended
TrueCopy for Mainframe Asynchronous R-VOL indicates its update sequence consistency with
respect to the other R-VOLs in the same group.
“Consistency Status for Suspended TrueCopy for
Mainframe Async P-Vols” (page 38) lists and describes the consistency status descriptions for
suspended TrueCopy for Mainframe Asynchronous R-VOLs.
When a TrueCopy for Mainframe pair is suspended, whether user-requested or due to failure, the
MCU generates sense information to notify the host(s). If the host system supports IBM PPRC (and
the PPRC support RCU option is enabled), this notification results in an IEA494I and/or IEA491E
system console message which indicates the reason for suspension.
If you need write access to an R-VOL, you must release the pair.
Table 9 Suspend Types
Description Applies to Suspend Type
The user suspended the pair from the
MCU using the M-VOL Failure option.
The R-VOL suspend type is by MCU. M-VOL (TrueCopy for Mainframe Sync
only) M-VOL by operator
The user suspended the pair from the
MCU or RCU using the R-VOL option. M-VOL, R-VOL R-VOL by operator
The RCU received a request from the
MCU to suspend the pair. The M-VOL
suspend type is M-VOL by Operator or
R-VOL by Operator. R-VOL by MCU
36 About TrueCopy for Mainframe Operations