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1-8 Overview
Copyright © 2009 by LSI Corporation. All rights reserved.
1.5 Benefits of the SAS Interface
SAS is a serial, point-to-point, enterprise-level device interface that
leverages the proven SCSI protocol set. SAS is a convergence of the
advantages of SATA II, SCSI, and Fibre Channel, and is the future
mainstay of the enterprise and high-end workstation storage markets.
SAS offers a higher bandwidth per pin than parallel SCSI, and it
improves signal and data integrity.
The SAS interface uses the proven SCSI command set to ensure reliable
data transfers, while providing the connectivity and flexibility of
point-to-point serial data transfers. The serial transmission of SCSI
commands eliminates clock-skew challenges. The SAS interface
provides improved performance, simplified cabling, smaller connectors,
lower pin count, and lower power requirements when compared to
parallel SCSI.
SAS controllers leverage a common electrical and physical connection
interface that is compatible with Serial ATA technology. The SAS and
SATA II protocols use a thin, 7-wire connector instead of the 68-wire
SCSI cable or 26-wire ATA cable. The SAS/SATA II connector and cable
are easier to manipulate, allow connections to smaller devices, and do
not inhibit airflow. The point-to-point SATA II architecture eliminates
inherent difficulties created by the legacy ATA master-slave architecture,
while maintaining compatibility with existing ATA firmware.
1.5.1 PCI Express Architecture
PCI Express is a local bus system designed to increase data transfers
without slowing down the central processing unit (CPU). You can install
MegaRAID PCI Express RAID controllers in PCI Express computer
systems with a standard bracket type. With these controllers in your
system, you can connect SAS devices and SATA II devices over the bus.
Note:
Some PCI-E slots support PCI-E graphics cards only; if a
RAID controller is installed on those PCI-E slots, it will not
function.
PCI Express goes beyond the PCI specification in that it is intended as
a unifying I/O architecture for various systems: desktops, workstations,
mobile, server, communications, and embedded devices.