Hitachi AMS 2000 User Manual page 222

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).
D
data path
See remote path.
data pool
One or more disk volumes designated to temporarily store un-
transferred differential data (in the local storage system or snapshots
of backup data in the remote storage system). The saved snapshots are
useful for accurate data restoration (of the P-VOL) and faster remote
takeover processing (using the S-VOL).
data volume
A volume that stores database information. Other files, such as index
files and data dictionaries, store administrative information (metadata).
differential-data
The original data blocks replaced by writes to the primary volume. In
Copy-on-Write, differential data is stored in the data pool to preserve
the copy made of the P-VOL to the time of the snapshot.
differential data control
The process of continuously monitoring the differences between the
data on two volumes and determining when to synchronize them.
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Glossary–4
Hitachi AMS 2000 Family TrueCopy Extended Distance User Guide
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