Serial Attached SCSI (SAS) cables are used to connect an array of hard drives to other SAS devices (controllers, hard drives, SAN storage area network, etc). SAS cables can have data transfer rates of 3Gbps, 6Gbps, or 12Gbps with 22.5Gbps in development. These cables have 4 lanes, using a point-to-point serial protocol that moves data to and from storage devices. SAS solutions are widely used in data centers, businesses and sometimes even in small offices.

When to choose SAS:

  • When performance is priority
  • If future scalability is important
  • The need for greater flexibility in critical server applications is required

The fall of Parallel SCSI and rise of SAS

Although SAS and parallel SCSI both use the SCSI command set, how they move data from one place to another is very different. The SAS “bus” operates 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.

Generally speaking, SAS is faster and more flexible than parallel SCSI, and provides more options for building your storage space. With the retirement of parallel SCSI we now consider SAS and SATA to be the standard for connecting network drives. SAS is geared towards critical network applications and SATA is better suited towards consumer desktop needs. SAS lets you mix SAS and SATA disk drives together, and lets you connect many more devices.

Similarities

  • Both SATA and SAS connectors can be on the same cable assembly.
  • Both types of HDD drives plug into the SAS backplane.
  • Both types of drives are interchangeable within a SAS drive bay module.
  • Both are long-proven technologies with worldwide acceptance.

Differences

  • SATA backplane cannot accept SAS drives.
  • SAS backplane can accept SATA drives.
  • SATA drives are less expensive than SAS.
  • SAS drives have:

– Dual porting capability

– Faster spindle speeds

  • SAS drives undergo more rigid testing specifications than SATA.
  • SAS drives have longer MTBF and duty cycle than SATA.
  • SAS offer more features than SATA:

– Variable sector sizes, LED indicators, dual ports, & more stable data integrity