HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and Configuration Guide

Glossary
Glossary–18 HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and
Configuration Guide
read ahead
caching
A caching technique for improving performance of synchronous
sequential reads by prefetching data from disk.
read caching
A cache management method used to decrease the subsystem response
time to a read request by allowing the controller to satisfy the request
from the cache memory rather than from the disk drives.
reconstruction
The process of regenerating the contents of a failed member data. The
reconstruct process writes the data to a spareset disk and incorporates
the spareset disk into the mirrorset, striped mirrorset, or RAIDset from
which the failed member came. See also regeneration.
reduced
Indicates that a mirrorset or RAIDset is missing one member because
the member has failed or has been physically removed.
redundancy
The provision of multiple interchangeable components to perform a
single function in order to cope with failures and errors. A RAIDset is
considered to be redundant when user data is recorded directly to one
member and all of the other members include associated parity
information.
regeneration
(1) The process of calculating missing data from redundant data. (2)
The process of recreating a portion of the data from a failing or failed
drive using the data and parity information from the other members
within the storageset. The regeneration of an entire RAIDset member is
called reconstruction. See also reconstruction.
remote copy
A feature intended for disaster tolerance and replication of data from
one storage subsystem or physical site to another subsystem or site.
Remote copy also provides methods of performing a backup at either
the local or remote site. With remote copy, user applications continue
to run while data movement goes on in the background. Data
warehousing, continuous computing, and enterprise applications all
require remote copy capabilities.
remote copy set
A bound set of two units, one located locally and one located remotely,
for long-distance mirroring. The units can be a single disk, or a
storageset, mirrorset, or RAIDset. A unit on the local controller is
designated as the “initiator” and a corresponding unit on the remote
controller is designated as the “target”.
request rate
The rate at which requests are arriving at a servicing entity.