Serial Attached SCSI (SAS) is a new generation of SCSI hard disks designed to allow for much higher speed data transfers. SAS does this by serial communication instead of the parallel method found in traditional SCSI devices.

SAS supports up to 16,256 addressable devices per port and point to point data transfer speeds up to 3 Gbit/s, but is expected to reach 10 Gbit/s by the year 2010. The SAS connector is much smaller than traditional parallel SCSI connectors allowing for small 2.5 inch drives.

The physical SAS connector is form factor compatible with SATA, allowing for much cheaper SATA drives to connect to a SAS backplane. SAS drives are not compatible on a SATA bus and have their physical connector keyed to prevent any plugging into a SATA backplane.

Serial Attached SCSI supports three transport protocols:

• Serial SCSI Protocol (SSP) - Supporting SAS disk drives
• Serial ATA Tunneling Protocol (STP) - Supporting SATA disks
• Serial Management Protocol (SMP) - Supporting SAS Expanders

References

SAS General Overview