Full-duplex with link aggregation (wide ports at 24 Gbit/s)
3.0 Gbit/s at introduction, 6.0 Gbit/s,
22.2 Gbit/s planned
8 meter external cable
128 device port expanders (16K + total devices)
Software-transparent with SCSI
Serial Attached SCSI (SAS) is a technology designed to move data to and from computer storage devices such as hard drives and tape drives. It is a point-to-point serialprotocol that replaces the parallel SCSI. SCSI first appeared in the mid 1980s in corporate data centers. SAS uses the standard SCSI command set. At present it is slightly slower than the final parallel SCSI implementation, but in 2009 it will double its present speed to 6 Gbit/s. This will permit much higher speed data transfers. The protocol is "downwards"-compatible with second generation SATA drives. These drives may be connected to SAS backplanes (controllers), but SAS drives can not be connected to SATA backplanes.
The SAS protocol is developed and maintained by the T10 technical committee of the International Committee for Information Technology Standards (INCITS) and promoted by the SCSI Trade Association (SCSITA).
The SAS bus is
point-to-point while the SCSI bus is
multidrop. Each SAS device is connected by a dedicated link to the initiator, unless an expander is used. If one initiator is connected to one target, there is no opportunity for contention; with parallel SCSI, even this situation could cause contention.
SAS has no
termination issues and does not require terminator packs like parallel SCSI.
SAS supports up to 16,384 devices through the use of expanders while Parallel SCSI is limited to 8, 16, or 32 devices (including the SCSI controller) on a single channel.
SAS supports a higher transfer speed (1.5 OR 3.0
Gbit/s) than most parallel SCSI standards. The speed is realized on each initiator-target connection, hence higher throughput whereas in parallel SCSI the speed is shared across the entire
SAS controllers are required by the standard to support SATA devices.
Both SAS and parallel SCSI use the SCSI command-set.