Unified Serial RAID Controllers for PCIe

SAS Vs. SATA

Can you tell them apart? The upper connectors are SATA (individual connectors), while the lower one belongs to a Seagate Savvio SAS drive, carrying the continuous connector for data and power.

Both SAS and SATA are based on full-duplex, switched serial point-to-point connections, which means that there is no need to manually assign device IDs or to terminate the connections, and data can be sent and received simultaneously. SAS and SATA also facilitate device hot-plugging. Speeding up parallel protocols such as Ultra320 SCSI either required a wider bus, which requires more wires, or faster clock speeds, which causes problems with signal delays. Serial point-to-point interconnects, however, can simply be bundled. SAS makes use of this technological principle, combining multiple SAS connects to hook up to external appliances.

Mechanically, there is only one difference between SAS and SATA: while both use the same pinout for data and power connections, the two connectors are physically separated for SATA. For SAS, the two connector segments were merged, which makes it possible to attach a SAS drive to a SATA controller using the continuous connector, but you cannot hook up a SAS hard drive to a SATA controller using the SATA connector (SFF 8482).

Performance wise, there is not much of a difference between the two interfaces. Serial ATA 2.5 provides a maximum bandwidth of 3 Gbit/s per port, using an 8/10 bit encoding, which results in a 2.4 Gbit/s or 300 MB/s bandwidth that can be used for actual data. The same applies for SAS, and the roadmap provides a road to 6 and 12 Gbit/s, resulting in 600 MB/s and 1,200 MB/s bandwidth per port.

SAS on the left, SATA on the right hand side.

The Mini SAS 4i connector is used (SFF-8087) to create so-called SAS wide ports, which typically consist of four SAS connections.