HP StorageWorks XP Remote Web Console Software - Manual (Page 65)

volumes (3390-3A/B/C). TrueCopy for Mainframe can copy data between volumes with the same
emulation and capacity (for example, 3390-3R to 3390-3R), and can also copy from smaller
volumes to larger volumes* (for example, 3390-3 to 3390-9 ) of the same emulation (VTOC
expansion must be used). TrueCopy for Mainframe also supports the Virtual LVI/LUN feature of
the XP disk array, enabling you to establish TrueCopy for Mainframe pairs with custom-size LVIs
as well as standard-size LVIs. When custom-size LVIs are assigned to TrueCopy for Mainframe
pairs, the R-VOL must have the same or larger capacity than the M-VOL. The TrueCopy for
Mainframe software displays the LVI of the M-VOLs and R-VOLs.
CAUTION: If you utilize TrueCopy for Mainframe to copy from a smaller volume to a larger
volume, you will not be able to perform TrueCopy for Mainframe operations in the reverse direction
(from the secondary site to the primary site) after a disaster has occurred and the secondary site
was used for production. If the SUSPEND command is issued from Business Continuity Manager,
you will not be able to use the Secondary Volume R/W option and Reverse option. This restriction
exists because TrueCopy for Mainframe does not support copying from a larger volume to a smaller
volume. HP strongly recommends that this capability (copying from a smaller volume to a larger
volume) only be used for data migration purposes.
CAUTION: If you use a Fujitsu operating system, and utilize TrueCopy for Mainframe Asynchronous
to copy from a smaller capacity of M-VOL to the larger capacity of R-VOL, an error will occur when
the write operation will be performed to the former R-VOL after the pair has been released. If the
write operation is required on this volume, make the capacity of M-VOL and R-VOL same, and
then create a pair.
Accessing TrueCopy for Mainframe M-VOLs and R-VOLs
Write operations to a TrueCopy for Mainframe M-VOL which specify normal authorization are
duplicated on the R-VOL of the TrueCopy for Mainframe pair. Write operations with diagnostic or
device support authorization (for example, ICKDSF) are completed at the M-VOL but are not
duplicated at the R-VOL. Therefore, you must suspend a TrueCopy for Mainframe pair before
performing ICKDSF media maintenance on the M-VOL. For more information, see
“ICKDSF
Considerations for TrueCopy for Mainframe Volumes” (page 166) .
To ensure maximum data integrity during normal TrueCopy for Mainframe operations, the RCU
rejects all read and write operations issued by a host to a TrueCopy for Mainframe R-VOL. If you
need read-only access to a TrueCopy for Mainframe R-VOL, you must have the R-VOL read option
enabled on the RCU, and you must suspend the pair to read the R-VOL. The R-VOL read option
can only be enabled by the HP service representative. If you need write access to a TrueCopy for
Mainframe R-VOL (for example, to perform ICKDSF), you must release the pair from the RCU to
change the R-VOL pair status to simplex.
Cache, NVS, and DASD Fast Write
Cache and nonvolatile storage (NVS) must be operable for both the MCU and RCU of a TrueCopy
for Mainframe pair. If not, the Add Pair operation will fail. The remote storage system cache should
be configured to adequately support the TrueCopy for Mainframe remote copy workloads as well
as any local workload activity.
DASD fast write (DFW) is required at the MCU and RCU only when the DFW-to-R-VOL required
TrueCopy for Mainframe pair option is specified. If DFW to an R-VOL is blocked and the TrueCopy
for Mainframe pair was established with the DFW-to-R-VOL required pair option, the MCU detects
DFW OFF at the R-VOL and suspends the pair. TrueCopy for Mainframe pairs which were
established using PPRC commands use the default value of not required and therefore are not
suspended when DFW to the R-VOL is blocked.
The DFW to R-VOL setting does not affect the I/O performance of the M-VOLs. If one side of cache
is closed due to an RCU failure, the TrueCopy for Mainframe copy operation still uses DFW. The
only difference between not required and required is that new pairs cannot be established with
Requirements and Restrictions 65