Hitachi MK-97DF8018-00 User Manual
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Glossary–4
Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
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configuration definition file
The configuration definition file describes the system configuration for
making CCI operational in a TrueCopy Extended Distance Software
environment. The configuration definition file is a text file created and/
or edited using any standard text editor, and can be defined from the
PC where the CCI software is installed. The configuration definition file
describes configuration of new TrueCopy Extended Distance pairs on
the primary or remote storage system.
consistency group (CTG)
A group of two or more logical units in a file system or a logical volume.
When a file system or a logical volume which stores application data, is
configured from two or more logical units, these multiple logical units
are managed as a consistency group (CTG) and treated as a single
entity. A set of volume pairs can also be managed and operated as a
consistency group.
consistency of S-VOL
A state in which a reliable copy of S-VOL data from a previous update
cycle is available at all times on the remote storage system A consistent
copy of S-VOL data is internally pre-determined during each update
cycle and maintained in the remote data pool. When remote takeover
operations are performed, this reliable copy is restored to the S-VOL,
eliminating any data discrepancies. Data consistency at the remote site
enables quicker restart of operations upon disaster recovery.
CRC
Cyclical Redundancy Checking, a scheme for checking the correctness
of data that has been transmitted or stored and retrieved. A CRC
consists of a fixed number of bits computed as a function of the data to
be protected, and appended to the data. When the data is read or
received, the function is recomputed, and the result is compared to that
appended to the data.
CTG
See Consistency Group.
cycle time
A user specified time interval used to execute recurring data updates
for remote copying. Cycle time updates are set for each storage system
and are calculated based on the number of consistency groups CTG.
cycle update
Involves periodically transferring differential data updates from the P-
VOL to the S-VOL. TrueCopy Extended Distance Software remote
replication processes are implemented as recurring cycle update
operations executed in specific time periods (cycles).