SAS vs parallel SCSI
SAS uses Serial transfer protocol to interface multiple devices hence lesser signaling overhead than parallel SCSI, resulting in higher speed.
No bus contention as SAS bus is point-to-point while SCSI bus is multidrop. Each device is connected by a dedicated bus to the initiator. Connection through expanders may appear to cause some contention, but this is transparent to the initiator.
SAS has no termination issues and does not require terminator packs like parallel SCSI.
SAS eliminates skew.
SAS supports higher number of devices (> 16384) while Parallel SCSI limits it to 16 or 32.
SAS supports higher transfer speed (1.5, 3.0 or 6.0 Gbps). The speed is realized on each initiator-target connection, hence higher throughput whereas in parallel SCSI the speed is shared across the entire multidrop bus.
SAS supports SATA devices.
SAS uses SCSI commands to interface with SAS End devices.
SAS vs SATA
SATA devices are uniquely identified by their port number connected to the Host bus adapter while SAS devices are uniquely identifed by their World Wide Name (WWN).
SATA 1 devices do not support command queuing while SAS devices support Tagged Command Queuing. Effort is on in SATA 2 to support command queuing using Native Command Queuing (NCQ).
SATA follows ATA command set and supports hard drives and CD-ROM drives only while SAS supports a wide range of devices including hard drives, scanners, printers, CD-ROM drives etc.
SAS hardware allows multipath I/O to devices while SATA does not. Effort is on in SATA 2 to use port multiplier to achieve mulitpathing.
SATA is primarily used for non-critical applications like home PC use while SAS, due to its robustness, can be used for critical server applications.
SAS error recovery and reporting are much cleaner than SATA.
SAS complements SATA and is not a competitor to SATA.
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