HP StorageWorks 4400 User Manual page 120

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 A cache management method used to decrease the subsystem response time to
caching 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.
2.
redundant power A capability of the Enterprise storage system racks and enclosures to allow
configuration continuous system operation by preventing single points of power failure.
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room temperature See
SCSI 1.
2.
SCSI-3 The ANSI standard that defines the operation and function of Fibre Channel
systems.
selective
The process whereby a controller presents a virtual disk only to the host computer
presentation which is authorized access.
serial transmission
A method of transmission in which each bit of information is sent sequentially
on a single channel rather than simultaneously as in parallel transmission.
SFP
Small Form-factor Pluggable transceiver.
small computer See SCSI.
system interface
120 Glossary
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 independ-
ently but can take over for the other in case of failure.
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.
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 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 configur-
ation provides protection against the loss or corruption of data.
ambient temperature.
Small Computer System Interface. An American National Standards Institute
(ANSI) interface which defines the physical and electrical parameters of a
parallel I/O bus used to connect computers and a maximum of 16 bus ele-
ments.
The communication protocol used a controller pair and the hosts. Specifically,
the protocol is Fibre Channel drive enclosure or SCSI on Fibre Channel.
SCSI is the higher command-level protocol and Fibre Channel is the low-
level transmission protocol. The controllers have full support for SCSI-2; ad-
ditionally, they support some elements of SCSI-3.