Hitachi AMS2100 User Manual page 193

Differential Management Logical Unit (DMLU)
The volumes used to manage differential data in a storage system. In a
TrueCopy Extended Distance system, there may be up to two DM
logical units configured per storage system. For Copy-on-Write and
ShadowImage, the DMLU is an exclusive volume used for storing data
when the array system is powered down.
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.
disaster recovery
A set of procedures to recover critical application data and processing
after a disaster or other failure. Disaster recovery processes include
failover and failback procedures.
disk array
An enterprise storage system containing multiple disk drives. Also
referred to as "disk array device" or "disk storage system."
DMLU
See Differential Management-Logical Unit.
dual copy
The process of simultaneously updating a P-VOL and S-VOL while using
a single write operation.
duplex
The transmission of data in either one or two directions. Duplex modes
are full-duplex and half-duplex. Full-duplex is the simultaneous
transmission of data in two direction. For example, a telephone is a full-
duplex device, because both parties can talk at once. In contrast, a
walkie-talkie is a half-duplex device because only one party can
transmit at a time.
E
entire copy
Copies all data in the primary volume to the secondary volume to make
sure that both volumes are identical.
extent
A contiguous area of storage in a computer file system that is reserved
for writing or storing a file.
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Hitachi AMS 2000 Family Copy-on-Write SnapShot User Guide
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