HP StorageWorks XP Remote Web Console Software - Manual (Page 48)

48 Hitachi TrueCopy z/OS for HP XP12000/XP10000 and SVS 200 storage systems
Accessing TrueCopy M-VOLs and R-VOLs
Write operations to a TC390 M-VOL that specify normal authorization are duplicated on the R-VOL of the
TC390 pair. Write operations with diagnostic or device support authorization, such as ICKDSF, are
completed at the M-VOL but are not duplicated at the R-VOL. Therefore, you must suspend a TC390 volume
pair before performing ICKDSF media maintenance on the M-VOL. For instructions on running ICKDSF on
TC390 volumes, see ” ICKDSF considerations for TrueCopy volumes ” on page 140.
To ensure maximum data integrity during normal TC390 operations, the RCU rejects all read and write
operations issued by a host to a TC390 R-VOL. If you need read-only access to a TC390 R-VOL, you must
have the R-VOL read option (see ” R-VOL read option ” on page 27) enabled on the RCU and you must
suspend the pair to read the R-VOL. The R-VOL read option can be enabled by the HP representative only.
If you need write access to a TC390 R-VOL (for example, to perform ICKDSF), you must delete the pair from
the RCU to change the R-VOL pair status to simplex. For instructions on running ICKDSF on TC390 volumes,
see ” ICKDSF considerations for TrueCopy volumes ” on page 140.
Cache, NVS, and DASD Fast Write
Cache and nonvolatile storage (NVS) must be operable for both the MCU and RCU of a TC390 volume
pair. If not, the Add Pair operation will fail. The remote disk array cache should be configured to
adequately support the TC390 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 TC390
pair option (see ” Creating TrueCopy volume pairs (Add Pair) ” on page 125) is specified. If DFW to an
R-VOL is blocked and the TC390 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. TC390 pairs that 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 TC390 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).
Consistency groups
The TC390A consistency groups have the following requirements:
• All TC390A pairs must be assigned to one and only one consistency group.
• The maximum number of volume pairs in one consistency group is 4,096 (entire RCU).
• The maximum number of consistency groups established for one MCU-RCU pair is 128. The RCU
supports a maximum of 128 groups. This limit of 128 groups includes both TC390A groups and TC
Asynchronous groups (for example, 64 TC390A + 64 XP Continuous Access Asynchronous).
• Each update I/O to the M-VOLs in one consistency group must be time-stamped using a common timer
facility. The primary host system cannot access volume pairs of the same consistency group if the pairs
do not have a common timer reference.
• A consistency group must consist of TC390A pairs or XP Continuous Access Asynchronous pairs, but
not both.
• Only TC390A pairs that belong to the same CLPR can be allocated to one consistency group. For
further information on CLPR, see the HP StorageWorks XP Disk/Cache Partition user guide for the disk
array model.
Restrictions on volumes
If CSUSPEND or FREEZE command is used, TC390 M-VOLs may report SCP (State Change Pending) to the
host. If the CSUSPEND, or FREEZE command is issued to certain volumes (for example, active SPOOL,
PAGE, or CATALOG datasets, active SYSRES volume), the attached hosts may enter a deadlock condition
and may require a storage control IML to correct the condition.