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Glossary–6
Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
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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.
F
failover
The automatic substitution of a functionally equivalent system
component for a failed one. The term failover is most often applied to
intelligent controllers connected to the same storage devices and host
computers. If one of the controllers fails, failover occurs, and the
survivor takes over its I/O load.
fallback
Refers to the process of restarting business operations at a local site
using the P-VOL. It takes place after the storage systems have been
recovered.
Fault tolerance
A system with the ability to continue operating, possibly at a reduced
level, rather than failing completely, when some part of the system
fails.
FC
See fibre channel.