| 1-9 |
| 1394 |
The
Institute of Electrical and Electronics Engineers (IEEE) designation
for an interface developed for easy connection to consumer devices,
such as video and computer peripherals. |
| |
| A |
| Active
Negation |
Provides
better noise immunity on the complex SCSI bus. |
| Active
Termination |
An
active terminator actually has one or more voltage regulators
to produce the termination voltage, rather than using resistor
voltage dividers. |
| ASPI |
Advanced
SCSI programming Interface. A standard SCSI software interface
that acts as a liaison between host adapters and SCSI device
drivers. ASPI enables host adapters and device drivers to share
a single SCSI hardware interface. |
| Asynchronous
Data Transfer |
A
method of SCSI data transfer. This is the type of transfer rate
originally introduced with SCSI 1. With this type of transfer
method, transfer rates of 2 MBytes/sec are common. See also
SYNCHRONOUS TRANSFER. |
| |
| B |
| BIOS |
An
acronym for Basic Input/Output System. This is usually an EPROM
with computer program instructions in it. A motherboard BIOS
(usually by companies such as Phoenix, Award, and AMI) controls
the basic functions of the computer (such as controlling the
keyboard, monitor, etc.). With a SCSI host adapter, the BIOS
is used to control SCSI hard disk drives and perform the boot
function. If a host adapter does not have a BIOS, then hard
disk drives controlled by that host adapter cannot be used to
boot from (booting must be done from another source, such as
floppy, IDE, or another SCSI host adapter with a BIOS). The
BIOS must be enabled in order to function (e.g. a host adapter
with a BIOS that is disabled acts the same as a host adapter
without a BIOS). |
| Bus
Mastering |
A
high performance method of data transfer in which the host adapter's
on-board processor handles the transfer of data directly to
and from a computer's memory without intervention from the computer's
microprocessor. This is the fastest method of data transfer
available for multitasking operating systems. |
| |
| C |
| Command
Queueing |
In
SCSI-1, initiators were limited to one command per LUN e.g.
a disk drive. Now up to 256 commands can be outstanding to one
LUN. The target is allowed to re-sequence the order of command
execution to optimize seek motions. Queued commands require
Tag messages which follow the Identify. |
| |
| D |
| Differential |
A
term referring to the electrical characteristics of the signals
used on the SCSI bus interface. Differential signals occupy
two conductors with a positive (+) and negative (-) polarity
component of the signal. This minimizes the effect of common
mode signal noise and allow the SCSI bus to operate reliably
over greater distances at a higher speed. |
| DMA |
A
mechanism that allows hardware control of the transfer of streams
of data to or from the main memory of a computing system. The
mechanism may require setup by the host software. After initialization,
it automatically sequences the required data transfer and provides
the necessary address information. |
| |
| E |
| EEPROM |
An
acronym for Electrically Erasable Programmable Read Only Memory.
These devices can be erased instantly. |
| Exclusive
OR (XOR) |
A
process based on a mathematical algorithm that is used by RAID
levels 2, 3, 4 and 5 to compare computer data (binary 0s and
1s) created by a read request during a drive failure or by a
write request. The result of the XOR process is parity information
that will be stored along with data in case of a disk failure.
|
| |
| F |
| Fast
SCSI |
Provides
for performance and compatibility enhancements to SCSI-1 by
increasing the maximum synchronous data transfer rate on the
SCSI bus from 5 MBytes/sec to 10 MBytes/sec. |
| Fast
Wide SCSI |
16
bit SCSI asynchronous commands with Synchronous data transfer
rates up to 20 megabytes per second. Bipolar technology with
Open collector or active negation single ended bus transceivers,
passive or active termination. and Differential (Now called
HVD – High Voltage differential) bus transceivers based on EIA
485 allowed in SCSI-2. |
| Fibre
Channel |
A
high-end storage interface for fast data transfer in storage
networks or data centers. |
| Firewire |
The
Apple trademark for the IEEE 1394 interface. |
| |
| G |
| |
|
| |
| H |
| Hot
Spare |
RAID
storage feature that allows a spare drive to be configured on-line
for automatic reconstruction in the event of a disk failure.
|
| Hot
Swap |
A
storage system's ability to allow the removal and replacement
of a disk drive while users are on-line and accessing data.
|
| |
| I |
| i.Link |
The
Sony trademark for the IEEE 1394 interface. |
| Interrupt
13 |
This
is the software interrupt for disk I/O used by DOS. DOS does
'Interrupt 13 calls' to read or write from a diskettes. A SCSI
host adapter translates these Interrupt 13 commands into SCSI
commands for SCSI disk drives. |
| Interrupt
19 |
This
is the software interrupt that handles the boot function. The
boot code is typically handled by the motherboard BIOS, but
can optionally be handled by the host adapter BIOS with some
Adaptec host adapters. |
| IRQ |
Interrupt
Request Channel. The IRQ of a host adapter can be changed to
several different settings by changing jumpers and/or switch
settings on the adapter board. |
| Isochronous
Data Transfer |
Data
transfer that is matched to a clock so that data is sent at
a fixed rate. (Necessary for video and audio connections to
devices such as TVs) |
| |
| J |
| JBOD |
Just
a Bunch Of Drives. Refers to a rank of disks without data redundancy
or striping. |
| |
| K |
| |
|
| L |
| |
|
| M |
| Mirroring |
Also
known as RAID 1 or duplexing (when using two host bus adapters).
Full redundancy is obtained by duplicating all data from a primary
disk on a secondary disk. The overhead of requiring 100% data
duplication can costly when using more than two drives. |
| MTBDL |
Mean
time before data loss. The average time before the failure of
a RAID system component causes data to be lost or corrupted.
|
| MTBF |
Mean
time between failure. Used to measure computer component average
reliability/life expectancy. MTBF is not as well-suited for
measuring the reliability of RAID storage systems as MTBDL,
MTTR or MTDA because it does not account for RAID's ability
to recover from a drive failure. In addition, enhanced enclosure
environments used with RAID systems to increase uptime can further
limit the applicability of MTBF ratings for RAID solutions.
|
| MTDA |
Mean
time of data availability. The average time before non-redundant
components fail, causing data inaccessibility without loss or
corruption. |
