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C141-F037-02EN GL - 1
Actuator
A head positioning assembly. The actuator
consists of a voice coil motor, head arms, and a
servo head which positions the read/write (R/W)
head.
Bus condition
An asynchronous condition for changing the
SCSI bus status. The bus condition is
ATTENTION or RESET.
Bus phase
SCSI bus status. A SCSI bus is in the BUS FREE
phase, ARBITRATION phase, SELECTION phase,
RESELECTION phase, or INFORMATION
TRANSFER phase. The INFORMATION
TRANSFER phase is further classified into the
DATA IN phase, DATA OUT phase, COMMAND
phase, STATUS phase, MESSAGE IN phase, or
MESSAGE OUT phase.
Command (CDB)
A request for an input/output operation of a target
Command descriptor block (CDB)
A series of data that consists of input/output
operation commands. The CDB is transferred
from an initiator to a target.
Common command set (CCS)
Standard SCSI logical specifications established
by a work section meeting of the American
National Standards Institute (ANSI). CCS
specifies the functions that direct access devices
(e.g., disk drives) must have.
Disconnection
Processing to temporarily cancel the connection of a
target with a SCSI bus and an initiator. A target is
disconnected when the SCSI bus is not needed
during command processing in the target.
Disk enclosure (DE)
A device that contains rigid disks, an assembly
motor mounted spindle, an actuator, heads, and
air filters. The DE is sealed to protect the
internal mechanism from external dust.
Initiator (INIT)
A SCSI device that initiates input/output
operation on an SCSI bus
Logical unit
A unit in which an input/output operation on a
SCSI bus can be performed
Logical unit number (LUN)
A unit number which identities a logical unit
Mean time between failures (MTBF)
MTBF is calculated as follows: total operation
time/total number of errors in running disk drive
where, the total operation time is the total power-
on time.
Mean time to repair (MTTR)
Average time taken by a service engineer to
diagnose and repair a faulty device
Message
Control information to be transferred between an
initiator and a target operating on a SCSI bus.
This information is used to control a series of bus
phases and an execution sequence of input/output
operations.
Positioning time
The sum of seek time and average rotational delay
Ready LED
A green light emitting diode mounted on the
front of the disk drive. The ready LED can
indicate the disk drive ready state or the disk
drive selection state.
GLOSSARY