HP StorageWorks IBM AIX Kit V3.0B for Enterprise Virtual Array Installation and Configuration Guide (AA-RUHAB-TE, October 2003)

Glossary
54 IBM AIX Kit V3.0B for Enterprise Virtual Array Installation and Configuration 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 host can change the preferred path of a virtual disk at any time. The primary purpose
of preferring a path is load balancing.
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.
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 which 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.
small computer system interface
See SCSI.