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Glossary
121Command View EVA Storage System Scripting Utility Reference Guide
preferred path
A preference for which controller of the controller pair manages the virtual disk. This preference is
set by the user through the Command View EVA when creating the virtual disk. A user can change
the preferred path of a virtual disk at any time. The main purpose of selecting a preferred path is
load balancing.
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.
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.
redundancy
■ 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.
■ 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.
SCSI (small computer system interface)
■ An American National Standards Institute (ANSI) interface that defines the physical and
electrical parameters of a parallel I/O bus used to connect computers and a maximum of 16 bus
elements.
■ The communication protocol used between a controller pair and the hosts. Specifically, the
protocol is FC-AL or SCSI on a 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; additionally, they support some elements of SCSI-3.
SCSI-3
The ANSI standard that defines the operation and function of Fibre Channel systems.