Dell PERC 4/SI - Manual (Page 69)

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Glossary
Dell™ PowerEdge™ Expandable RAID Controller 4/Di/Si and 4e/Di/Si User's Guide
A • B • C • D • F • G • H • I • L • M • N • O • P • R • S • T • W
Adapter Swapping
When an adapter fails, a a replacement can be inserted and connected to the existing set of drives. Dell supports adapter swapping only when all the
attached disks are migrated to a new adapter that has a clear configuration.
Array
An array of disk drives combines the storage space on the disk drives into a single segment of storage space. The RAID controller can group disk drives on one
or more SCSI channels into an array. A hot spare drive does not actively participate in an array.
Array Spanning
Array spanning by a logical drive combines storage space in two arrays of disk drives into a single, contiguous storage space in a logical drive. The logical
drives can span consecutively numbered arrays that each consist of the same number of disk drives. Array spanning promotes RAID level 1 to RAID level 10
and RAID level 5 to RAID level 50.
Asynchronous Operations
Operations that bear no relationship to each other in time and can overlap. The concept of asynchronous I/O operations is central to independent access
arrays in throughput-intensive applications.
BIOS
(Basic Input/Output System) The part of the operating system in an IBM PC-compatible system that provides the lowest level interface to peripheral devices.
The BIOS is stored in ROM in every IBM or compatible PC. BIOS also refers to the Basic Input/Input Output System of other "intelligent" devices, such as RAID
controllers.
Cached I/O
Specifies that reads are buffered in cache memory, but does not override the other cache policies, such as read ahead or write.
Caching
The process of utilizing a high speed memory buffer, referred to as a "cache", in order to speed up the overall read or write performance. This cache can be
accessed at a higher speed than a disk subsystem. To improve read performance, the cache usually contains the most recently accessed data, as well as data
from adjacent disk sectors. To improve write performance, the cache may temporarily store data in accordance with its write back policies. See the definition of
Write-Back for more information.
Channel
An electrical path for the transfer of data and control information between a disk and a disk adapter. A channel can also be referred to as a "bus", such as a
SCSI bus.
Clearing
In the BIOS Configuration Utility, the option used to delete data from physical drives.
Cold Swap
The replacement or exchange of a device in a system after powering down the system. In reference to disk subsystems, a cold swap requires that you turn
the power off before replacing a defective hard drive.
Consistency Check
An examination of the disk system to determine if all conditions are valid for the specified configuration (such as parity).
Data Transfer Capacity
The amount of data per unit time moved through a channel. For disk I/O, bandwidth is expressed in megabytes per second (MB/s).
Degraded Drive
A disk drive that has become non-functional or has decreased in performance.
Direct I/O
Specifies that reads are not buffered in cache memory, but does not override the other cache policies, such as read ahead or write.
Disk
A non-volatile, randomly addressable, rewriteable mass storage device, including both rotating magnetic and optical storage devices and solid-state storage
devices, or non-volatile electronic storage elements.