Dell PERC 4/DC - Manual (Page 90)

Disk Subsystem
A collection of disks and the hardware that connects them to one or more host systems. The hardware can include an intelligent controller, or the disks can
attach directly to a host system.
Double Buffering
A technique that achieves maximum data transfer bandwidth by constantly keeping two I/O requests for adjacent data outstanding. A software component
begins a double-buffered I/O stream by issuing two requests in rapid sequence. Thereafter, each time an I/O request completes, another is immediately
issued. If the disk subsystem is capable of processing requests fast enough, double buffering allows data to be transferred at the full-volume transfer rate.
Failed Drive
A drive that has ceased to function or consistently functions improperly.
Firmware
Software stored in read-only memory (ROM) or Programmable ROM (PROM). Firmware is often responsible for the startup routines and low-level I/O processes
of a system when it is first turned on.
FlexRAID Power Fail Option
The FlexRAID Power Fail option allows drive reconstruction, rebuild, and check consistency to continue when the system restarts because of a power failure,
reset, or hard boot. This is the advantage of the FlexRAID option. The disadvantage is, once the reconstruction is active, the performance is slower because an
additional activity is running.
Formatting
The process of writing zeros to all data fields in a physical drive (hard drive) to map out unreadable or bad sectors. Because most hard drives are factory
formatted, formatting is usually only done if a hard disk generates many media errors.
GB
(gigabyte) 1,073,741,824 bytes. It is the same as 1,024 MB (megabytes).
Host System
Any system to which disks are directly attached. Mainframes, servers, workstations, and personal systems can all be considered host systems.
Hot Spare
A stand-by drive ready for use if another drive fails. It does not contain any user data. Up to eight hard drives can be assigned as hot spares for an adapter.
Hot Swap
The substitution of a replacement unit in a disk subsystem for a defective one, where the substitution can be performed while the subsystem is running
(performing its normal functions). Hot swaps are manual. The backplane and enclosure must support hot swap in order for the functionality to work.
IDE
(Integrated Device Electronics) Also known at ATA (Advanced Technology Attachment), this is a type of interface for the hard drive, in which the controller
electronics are integrated onto the drive itself. With IDE, a separate adapter card is no longer needed; this reduces interface costs and makes it easier to
implement firmware.
I/O Driver
A host system software component (usually part of the operating system) that controls the operation of peripheral controllers or adapters attached to the
host system. I/O drivers communicate between applications and I/O devices, and in some cases participates in data transfer.
Initialization
The process of writing zeros to the data fields of a logical drive and generating the corresponding parity to bring the logical drive to a Ready state. Initializing
erases previous data and generates parity so that the logical drive will pass a consistency check. Arrays can work without initializing, but they can fail a
consistency check because the parity fields have not been generated.
Logical Disk
A set of contiguous chunks on a physical disk. Logical disks are used in array implementations as constituents of logical volumes or partitions. Logical disks are
normally transparent to the host environment, except when the array containing them is being configured.
Logical Drive
A virtual drive within an array that can consist of more than one physical drive. Logical drives divide the storage space of an array of hard drives or a spanned
group of arrays of drives. The storage space in a logical drive is spread across all the physical drives in the array or spanned arrays.
Mapping
The conversion between multiple data addressing schemes, especially conversions between member disk block addresses and block addresses of the virtual
disks presented to the operating environment.
MB
(Megabyte) An abbreviation for 1,048,576 (102) bytes. It is the same as 1,000 KB (kilobytes).