| slovo | definícia |
scsi-3
(foldoc) | SCSI-3
An ongoing standardisation effort to
extend the capabilities of SCSI-2. SCSI-3's goals are more
devices on a bus (up to 32); faster data transfer; greater
distances between devices (longer cables); more device classes
and command sets; structured documentation; and a structured
protocol model.
In SCSI-2, data transmission is parallel (8, 16 or 32 bit
wide). This gets increasingly difficult with higher data
rates and longer cables because of varying signal delays on
different wires. Furthermore, wiring cost and drive power
increases with wider data words and higher speed. This has
triggered the move to serial interfacing in SCSI-3. By
embedding clock information into a serial data stream signal
delay problems are eliminated. Driving a single signal also
consumes less driving power and reduces connector cost and
size.
To allow for backward compatibility and for added flexibility
SCSI-3 allows the use of several different transport
mechanisms, some serial and some parallel. The software
protocol and command set is the same for each transport.
This leads to a layered protocol definition similar to
definitions found in networking.
SCSI-3 is therefore in fact the sum of a number of separate
standards which are defined by separate groups. These
standards and groups are currently:
X3T9.2/91-13R2 SCSI-3 Generic Packetized Protocol
X3T9.2/92-141 SCSI-3 Queuing Model
X3T9.2/92-079 SCSI-3 Architecture Model
IEEE P1394 High Performance Serial Bus
X3T9.2/92-106 SCSI-3 Block Commands
X3T9.2/91-189 SCSI-3 Serial Bus Protocol
X3T9.2/92-105 SCSI-3 SCSI-3 Core Commands
SCSI-3 Common Command Set
X3T9.2/92-108 SCSI-3 Graphic Commands
X3T9.2/92-109 SCSI-3 Medium Changer Commands
X3T9.2/91-11 SCSI-3 Interlocked Protocol
X3T9.2/91-10 SCSI-3 Parallel Interface
X3T9.2/92-107 SCSI-3 Stream Commands
SCSI-3 Scanner Commands
Additional Documents for the Fibre Channel are also meant to
be included in the SCSI-3 framework, i.e.:
Fibre Channel SCSI Mapping
Fibre Channel Fabric Requirements
Fibre Channel Low Cost Topologies
X3T9.3/92-007 Fibre Channel Physical and Signalling Interface
Fibre Channel Single Byte Commands
Fibre Channel Cross Point Switch Topology
X3T9.2/92-103 SCSI-3 Fibre Channel Protocol (GPP & SBP)
As all of this is an ongoing effort of considerable
complexity, document structure and workgroups may change. No
final standard is issued yet.
In the meantime a group of manufacturers have proposed an
extension of SCSI-2 called Ultra-SCSI which doubles the
transfer speed of Fast-SCSI to give 20MByte/s on an 8 bit
connection and 40MByte/s on a 16-bit connection.
[Hermann Strass: "SCSI-Bus erfolgreich anwenden",
Franzis-Verlag Muenchen 1993].
(1995-04-19)
|
| | podobné slovo | definícia |
scsi-3
(foldoc) | SCSI-3
An ongoing standardisation effort to
extend the capabilities of SCSI-2. SCSI-3's goals are more
devices on a bus (up to 32); faster data transfer; greater
distances between devices (longer cables); more device classes
and command sets; structured documentation; and a structured
protocol model.
In SCSI-2, data transmission is parallel (8, 16 or 32 bit
wide). This gets increasingly difficult with higher data
rates and longer cables because of varying signal delays on
different wires. Furthermore, wiring cost and drive power
increases with wider data words and higher speed. This has
triggered the move to serial interfacing in SCSI-3. By
embedding clock information into a serial data stream signal
delay problems are eliminated. Driving a single signal also
consumes less driving power and reduces connector cost and
size.
To allow for backward compatibility and for added flexibility
SCSI-3 allows the use of several different transport
mechanisms, some serial and some parallel. The software
protocol and command set is the same for each transport.
This leads to a layered protocol definition similar to
definitions found in networking.
SCSI-3 is therefore in fact the sum of a number of separate
standards which are defined by separate groups. These
standards and groups are currently:
X3T9.2/91-13R2 SCSI-3 Generic Packetized Protocol
X3T9.2/92-141 SCSI-3 Queuing Model
X3T9.2/92-079 SCSI-3 Architecture Model
IEEE P1394 High Performance Serial Bus
X3T9.2/92-106 SCSI-3 Block Commands
X3T9.2/91-189 SCSI-3 Serial Bus Protocol
X3T9.2/92-105 SCSI-3 SCSI-3 Core Commands
SCSI-3 Common Command Set
X3T9.2/92-108 SCSI-3 Graphic Commands
X3T9.2/92-109 SCSI-3 Medium Changer Commands
X3T9.2/91-11 SCSI-3 Interlocked Protocol
X3T9.2/91-10 SCSI-3 Parallel Interface
X3T9.2/92-107 SCSI-3 Stream Commands
SCSI-3 Scanner Commands
Additional Documents for the Fibre Channel are also meant to
be included in the SCSI-3 framework, i.e.:
Fibre Channel SCSI Mapping
Fibre Channel Fabric Requirements
Fibre Channel Low Cost Topologies
X3T9.3/92-007 Fibre Channel Physical and Signalling Interface
Fibre Channel Single Byte Commands
Fibre Channel Cross Point Switch Topology
X3T9.2/92-103 SCSI-3 Fibre Channel Protocol (GPP & SBP)
As all of this is an ongoing effort of considerable
complexity, document structure and workgroups may change. No
final standard is issued yet.
In the meantime a group of manufacturers have proposed an
extension of SCSI-2 called Ultra-SCSI which doubles the
transfer speed of Fast-SCSI to give 20MByte/s on an 8 bit
connection and 40MByte/s on a 16-bit connection.
[Hermann Strass: "SCSI-Bus erfolgreich anwenden",
Franzis-Verlag Muenchen 1993].
(1995-04-19)
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