Project 2122 - Information
technology - Fibre Channel - Single-Byte
Command Code Sets-4 Mapping
Protocol (FC-SB-4)
This project proposal recommends the development of a FC-SB-4 standard that
defines a new mode
of operation that significantly improves the performance of certain types
of data transfer operations
compared to the existing FC-SB-3 protocol. The new mode of operation is referred
to as transport
mode and allows multiple device commands to be sent to a control unit in
a single Information Unit
(IU). Transport-mode operations utilize link-level protocols described by
the FC-4 Fibre Channel Protocol
(FCP) specification. The protocol and functions currently specified by FC-SB-3
and FC-SB-3-A1
will continue to be supported in FC-SB-4. It is intended that the FC-SB-4
Standard will be a complete
replacement for FC-SB-3 and FC-SB-1-A1.
Transport mode operations make use of a new IU, the transport-command-IU,
that is sent from a channel
to a control unit using the FCP link-level protocol. The transport-command
IU contains a list of devices
command words (DCW), each specifying a device command to be executed by the
control unit.
A single transport-response IU is returned to indicate completion or termination
of the DCWs specified
in the transport-command IU. Transport-data IUs are used to transport data
for read and write operations
as specified by FCP link-level protocols.
In transport mode, communication between the channel and control unit takes
place using a single
bidirectional exchange and utilizes fewer handshakes to close exchanges,
to transmit device commands
and to provide device status compared with the FC-SB-3 protocol. Performance
improvement
is most significant with I/O operations that are performing small block data
transfers (e.g., multiple
DCWs with data transfers of 25 kBytes or less) because of the reduction in
overhead relative to transfer
size. Certain types of complex I/O operations will still be required to use
the existing FC-SB-3 protocol.
The goal of the FC-SB-4 standard is to:
a) Define a new FC-SB-4 transport-mode protocol;
b) Incorporate the FC-SB-3/AM1 amendment;
c) Update all text references to current versions of existing standards;
and
d) Include changes required, technical or otherwise, for issues related to
the current FC-SB-3 protocol
as deemed necessary by the working group.