Manual

read ahead
caching
A cache ma nag em ent method used to decrease the subsystem response time to
a read request by allowing the controller to satisfy the request from the cache
memor y 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 de gree to which logical or phys ical elements
are protected by h aving 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
levelofdataprotection,themorestoragespaceisrequired.
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 condi
tioning 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
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.
room temperature See ambient temperature
SCSI 1. Small Computer System Inter face. 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
elements.
2. The communication protocol used between 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 suppor t for
SCSI-2; add itionally, they support some elements of SCSI-3.
SCSI-3 The ANSI standard that defines the op eration and function of Fibre Channel
systems.
SCSI-3 Enclosure
Services
See SES.
selective presenta-
tion
The process whereby a controller presents a virtual disk only to the h ost
computer 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.
SES SCSI-3 Enclosures Services.
Those services tha t establish the mechanical
environment, electrical environment, and external indicators and controls for the
proper o peration and m a intenance of devices within an enclosure.
Enterprise Virtual Array 3000/5000 user guide
151