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RS/6000 43P 7043 Models 150 and 260 Handbook
4.4 Serial Storage Architecture Overview
Serial Storage Architecture (SSA) is a high-speed serial interface that IBM
originally developed as a proprietary interface. The interface was
standardized in 1994 under the control of the ANSI X3T10.1 committee. SSA
is designed to overcome the bottlenecks of existing SCSI bus architectures.
originally developed as a proprietary interface. The interface was
standardized in 1994 under the control of the ANSI X3T10.1 committee. SSA
is designed to overcome the bottlenecks of existing SCSI bus architectures.
SSA is a single I/O interface that can effectively address the storage
requirements of a variety of computers, from PCs to supercomputers.
Combining the highest performance of a direct disk interface with low cost
connectivity and flexibility of network-wide attachment, SSA offers a reliable
and robust storage interface. Compared to newer interfaces such as Fibre
Channel-Arbitrated Loop (FC-AL) connection, which IBM announced in
October 1998 for the RS/6000 Enterprise Server model S7A, SSA is more
cost-effective while delivering equal or better performance. Compared to
today’s parallel interfaces such SCSI, SSA serial link connectivity provides
many benefits:
requirements of a variety of computers, from PCs to supercomputers.
Combining the highest performance of a direct disk interface with low cost
connectivity and flexibility of network-wide attachment, SSA offers a reliable
and robust storage interface. Compared to newer interfaces such as Fibre
Channel-Arbitrated Loop (FC-AL) connection, which IBM announced in
October 1998 for the RS/6000 Enterprise Server model S7A, SSA is more
cost-effective while delivering equal or better performance. Compared to
today’s parallel interfaces such SCSI, SSA serial link connectivity provides
many benefits:
• Enables hot-swapping and automatic configuration of new devices (with
out interrupting file service to users)
• Supports up to 128 total devices (including multiple initiator) in a single
SSA configuration, compared to a maximum of 16 devices for SCSI
• Provides configuration flexibility with up to 25 meters of separation
between devices
• Maximizes data transfer, currently enabling 80 MB/s of available
bandwidth
SSA uses shielded twisted pair (STP) cabling as a transport medium. There
are five conductors in the cable. Four are used for signal transmission, and
one is used as a shield. The twists in the cable eliminate crosstalk, and the
shielding eliminates electromagnetic interference (EMI). Thus, SSA can
function reliably with its nodes placed 25 m apart. IBM offers a fiber optic
extender that can extend this limit to 2400 m. The fiber optic extenders are
supplied in pairs to complete a string.
are five conductors in the cable. Four are used for signal transmission, and
one is used as a shield. The twists in the cable eliminate crosstalk, and the
shielding eliminates electromagnetic interference (EMI). Thus, SSA can
function reliably with its nodes placed 25 m apart. IBM offers a fiber optic
extender that can extend this limit to 2400 m. The fiber optic extenders are
supplied in pairs to complete a string.