Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

3-8 Preparing for TrueCopy for z/OS Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Accessing TrueCopy for z/OS M-VOLs and R-VOLs
Write operations to a TCz M-VOL which specify normal authorization are
duplicated on the R-VOL of the TCz pair. Write operations with diagnostic or
device support authorization (e.g., ICKDSF) are completed at the M-VOL but
are not duplicated at the R-VOL. Therefore, you must suspend a TCz pair
before performing ICKDSF media maintenance
on the M-VOL.
To ensure maximum data integrity during normal TCz operations, the RCU
rejects all read and write operations issued by a host to a TCz R-VOL. If you
need read-only access to a TCz 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 Hitachi representative. If you need
write access to a TCz R-VOL (e.g., 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 TCz pair. If not, the Add Pair operation will fail. The remote storage
system cache should be configured to adequately support the TCz 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 TCz pair option is specified. If DFW to an R-VOL is
blocked and the TCz 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.
TCz 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.
Note: 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 TCz copy
operation still uses DFW. The only difference between not required and
required is that new pairs cannot be established with the DFW-to-R-VOL
required option when one side of RCU cache is closed (the add pair operation
fails).