HP 3000 Enterprise Virtual Array - Manual (Page 226)

Glossary
226 Enterprise Virtual Array 3000 User Guide
read caching
A cache method used to decrease subsystem response times to a read request by allowing the
controller to satisfy the request from the cache memory rather than from the disk drives.
Reading data from cache memory is faster than reading data from a disk. The read cache is
specified as either On or Off for each virtual disk. The default state is on.
read ahead 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 reconstruction process
writes the data to a spare set disk and incorporates the spare set disk into the mirrorset, striped
mirrorset or RAID set from which the failed member came.
redundancy
1. Element Redundancy—The degree to which logical or physical elements are protected by
having another element that can take over in case of failure. For example, each loop of a
device-side loop pair normally works independently but can take over for the other in case
of failure.
2. Data Redundancy—The level to which user data is protected. Redundancy is directly
proportional to cost in terms of storage usage; the greater the level of data protection, the
more storage space is required.
redundant power configuration
A capability of the Enterprise Storage System racks and enclosures to allow continuous system
operation by preventing single points of power failure.
■ For a rack, two AC power sources and two power conditioning units distribute primary and
redundant AC power to enclosure power supplies.
■ For a controller or disk drive enclosure, two power supplies ensure that the DC power is
available even when there is a failure of one supply, one AC source, or one power
conditioning unit. Implementing the redundant power configuration provides protection
against the loss or corruption of data.
reporting group
An Enterprise Storage System controller pair and the associated disk drive enclosures. The
Enterprise Storage System controller assigns a unique decimal reporting group number to each
EMU on its loops. Each EMU collects disk drive environmental information from its own
sub-enclosure and broadcasts the data over the enclosure address bus to all members of the
reporting group. Information from enclosures in other reporting groups is ignored.