Adaptec MAN-00005-UG, Installation And User Manual

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several virtual disks whose entire capacity approximates
that of the underlying disk or array.
PCI
Peripheral Component Interconnect, a standardized
architecture that provides a high-speed data path between
peripherals and the CPU. PCI is a high-performance,
backplane interface, expansion slot architecture found on
PCs, Macintosh, and UNIX
®
workstations. PCI cards are
portable across hardware platforms with the help of various
software drivers.
Physical Device
Any device connected to some kind of hardware. For
example, SCSI disk, fibre disk, network disk, RAM disk,
etc.
Physical Disk Drive
A single hard disk drive. Each physical disk drive is
assigned a unique identification address.
Q
Queue
A line of things, commands, or data waiting to be handled,
usually in sequential order starting at the beginning or top
of the line or sequence.
R
RAID
Redundant Array of Independent Disks, a collection of two
or more disks working together in an array. RAID
controllers implement this technology to connect up to 15
SCSI devices per channel. The different forms of RAID
implementation are known as “RAID levels.” See also
Berkeley RAID Levels, Disk Array, and RAID Levels. The
system manager or integrator selects the appropriate RAID
level for a system. This decision will be based on which of
the following are to be emphasized: - Disk Capacity - Data
Availability (redundancy or fault tolerance) -Disk
Performance
RAID Controller
Low cost RAID controllers that use SCSI channels on the
motherboard.
RAID Levels
Disk array controllers support four RAID Advisory Board
approved (RAID 0, RAID 1, RAID 3, and RAID 5), two
special (RAID 0+1, and JBOD), and three spanned (RAID
10, 30, and 50) RAID levels. All DAC960, AcceleRAID,
and eXtremeRAID series controllers support these RAID
levels. See also Berkeley RAID Levels. Level 0: Provides
block “striping” across multiple drives, yielding higher
performance than is possible with individual drives. This
level does not provide any redundancy. Level 1: Drives are
paired and mirrored. All data is 100 percent duplicated on a
drive of equivalent size. Level 3: Data is “striped” across
several physical drives. Maintains parity information
which can be used for data recovery. Level 5: Data is
“striped” across several physical drives. For data
redundancy, drives are encoded with rotated XOR
redundancy. Level 0+1: Combines RAID 0 striping and
RAID 1 mirroring. This level provides redundancy through
mirroring. JBOD: Sometimes referred to as “Just a Bunch
of Drives.” Each drive is operated independently like a
normal disk controller, or drives may be spanned and seen
as a single drive. This level does not provide data
redundancy. Level 10: Combines RAID 0 striping and
RAID 1 mirroring spanned across multiple drive groups
(super drive group). This level provides redundancy
through mirroring and better performance than Level 1
alone. Level 30: Data is “striped” across multiple drive
groups (super drive group). Maintains parity information,
which can be used for data recovery. Level 50: Data is
“striped” across multiple drive groups (super drive group).
For data redundancy, drives are encoded with rotated XOR
redundancy.
Note: The host operating system drivers and
software utilities remain unchanged regardless of the level
of RAID installed. The controller makes the physical
configuration and RAID level implementation.
RAID Migration
A feature in RAID subsystems that allows for changing a
RAID level to another level without powering down the
system.
Recovery
The process of reconstructing data from a failed disk using
data from other drives.
Redundancy