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Hitachi Command Control Interface (CCI) User and Reference Guide 23
2.4.2 TrueCopy Async, TrueCopy Sync CTG, and Universal Replicator Volumes
Hitachi TrueCopy Asynchronous/Universal Replicator provides paired volumes which utilize
asynchronous transfer to ensure the sequence of writing data between the primary volume
and secondary volume. The sequence of writing data between the primary and secondary
volumes is guaranteed within each consistency (CT) group (see Figure 2.9).
Restrictions:
Group definition of TrueCopy Async/Universal Replicator/TrueCopy Sync CTG
volume: All volumes in a group must be contained within the same storage system. If
two or more groups of CCI include the same CT group (CTGID), then pair operation of the
group specification is handled in CT group entirety.
Registration of CTGID number and limitations: CCI registers CTGID to RAID disk array
automatically when paired volumes are created by paircreate command, and groups of
configuration definition files are mapped to CTGID. The maximum number of CT groups
is 256 for USP V/VM and USP/NSC (CTGID0 to CTGID255), 128 for 9900V (CTGID0 to
CTGID127), and 64 for 9900 (CTGID0-CTGID63) (16 for 7700E). TrueCopy Async/Universal
Replicator pair command will be terminated with EX_ENOCTG when the maximum
number of CT groups is exceeded.
Relationships between CTGID and Journal group ID: CT group numbers 0-127 are used
for TrueCopy Asynchronous, TrueCopy Sync CTG, and Universal Replicator. The rest of
the CT group numbers 128-255 are used only for Universal Replicator, and are mapped to
the journal groups.
Table 2.5 Assignment of CT Groups
CTG Assignment
0 -127 TrueCopy Async
TrueCopy Sync CTG
CTG 0-127
Universal Replicator JNG 0-127
128 - 255 Universal Replicator JNG 128-255
At-time Split for TrueCopy Sync CTG: The operation for making data consistency is only
supported by the following option:
– pairsplit –g <group> ... [-r]
– pairsplit –g <group> ... -rw
TrueCopy Asynchronous/Universal Replicator volumes have the following characteristics:
PAIR state: A Hitachi TrueCopy Async pair changes to the PAIR status as soon as all
pending recordsets have been placed in the queue at the primary volume, without
waiting for the updates to complete at the secondary volume.
Pair splitting: When a TrueCopy Async pair is split or deleted, all pending recordsets at
the primary volume are sent to the secondary volume, then the pair status changes to
PSUS or SMPL. For pairsplit only, updates for the primary volume which occur during and
after the pairsplit operation are marked on the bitmap of the primary volume.