Document

Integration Guide for New Dual-Core Intel

Xeon

Processor-Based Servers (or Workstations) Rev 1.0

3) SAS HDD

SAS (Serial Attached SCSI) is a point-to-point architecture in which all storage devices connect directly

to a SAS port rather than sharing a common bus as traditional SCSI devices do. Point-to-point links

increase data throughput and improve the ability to locate and fix disk failures. More importantly, the

SAS architecture solves the clock skew and signal degradation problems of parallel SCSI at higher

signaling rates. SAS inherits its command set from parallel SCSI, frame formats from Fibre Channel, and

physical characteristics from Serial ATA.

The SAS and SATA technologies have several common features, including low-voltage differential

signaling, 8b/10b encoding, and full duplex communication. The Serial Attached SCSI standards

committee designed the SAS infrastructure to be compatible with SATA drives, allowing the coexistence

of both storage technologies in the same system and opening the door to SATA scalability. Because the

SAS architecture features a proven SCSI command set, advanced command queuing, and advanced

verification/error correction, SAS is the ideal solution for mission-critical enterprise storage applications.

z Performance

The speed of the first-generation SAS link is 3.0 gigabits/second (Gb/s). The speed of the

second-generation SAS link will be 6.0 Gb/s . SAS links are full duplex; they send and receive

information simultaneously, thereby reducing a major source of latency. The SAS interface allows for

combining multiple links to create 2x, 3x, or 4x connections for scalable bandwidth.

z SAS/SATA interoperability

The SAS architecture enables system designs that deploy both SAS and SATA devices, a

breakthrough for enterprise customers. This capability provides a broad range of storage solutions

that give IT managers the flexibility to choose storage devices based on reliability, performance, and

cost.

z Greater scalability

Serial Attached SCSI enables highly scalable topologies—internal, external, or a combination of

both—to give manufacturers and customers the flexibility to design and deploy a range of solutions.

The Serial ATA Tunneling Protocol (STP) enables SAS HBAs to communicate with SATA devices

through expanders and, therefore, is key to SATA scalability in the SAS domain.

USEFUL INFORMATION

z More detail information about the disk interface technology can be found at

http://www.intel.com/technology/serialATA/pdf/NP2108.pdf