Avago Technologies Cache Protection for RAID Controller Cards - Manual (Page 8)

LSI Corporation
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12Gb/s MegaRAID SAS RAID Controllers User Guide
April 2014
Chapter 1: Overview
Benefits of the SAS Interface
The following figure shows an example of a SAS RAID controller configured with an LSISASx12 expander that is
connected to SAS drives, SATA III drives, or both.
Figure 2 Example of an LSI SAS RAID Controller Configured with an LSISASx12 Expander
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, SCSI, and Fibre Channel, and it 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 protocols and the SATA III protocols use a thin, 7-wire connector instead of the 68-wire SCSI cable
or 26-wire ATA cable. The SAS/SATA III connector and cable are easier to manipulate, allow connections to smaller
devices, and do not inhibit airflow. The point-to-point SATA III 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® (PCIe) is a local bus system designed to increase data transfers without slowing down the central
processing unit (CPU). You can install MegaRAID PCIe RAID controllers in PCIe computer systems with a standard
bracket type. With these controllers in your system, you can connect SAS devices and SATA devices over the bus.
NOTE Some PCIe slots support only PCIe graphics cards. RAID controllers
installed in these PCIe slots do not function.
PCIe goes beyond the PCI specification in that it is intended as a unifying I/O architecture for various systems:
desktops, workstations, mobile devices, servers, communications, and embedded devices.
LSISASx12
Flash ROM/
NVSRAM/
SRAM
I 2 C/UART
LSISASx12
PCI Express Interface
8
SRAM
SRAM SDRAM
Peripheral
Bus
72-bit DDR3
with ECC
Interface
LSISAS3108
PCI Express to SAS ROC
SAS RAID Controller
Expander Expander