SAS Interface Full Interconnect Guide (i)

Why are there so many SAS cables

Rome is not built in a day, and a norm from the birth to the development of gradually mature is far from the day's work. In the IT industry in particular, any technology is evolving itself, as is the SAS (serial attached SCSI, serial SCSI) specification. As a successor to parallel SCSI, the SAS specification has been out of sight for some time now. During the years that SAS passed, its specifications have been improved, although the underlying agreement to retain, basically not too many changes, but the specifications of the external interface connector has undergone many changes, this is the SAS to adapt to the market environment to make adjustments, with these "accumulated Bujikuibu and thousands of miles" of continuous improvement, The SAS specification is becoming more mature, and the interface connectors with different specifications can be regarded as witnesses of SAS development history.

Here we need to distinguish between the "port" and the "Interface Connector" (connector) concept. The port of the hardware device is also called the interface, its electrical signal is defined by the interface specification, and the quantity depends on the design of the control chip (Controller IC, also including ROC). But the interface or port, all must rely on an entity's manifestation--mainly pin and connectors, can play the role of the connection, and then constitute the data path. As a result, there are interface connectors that are always used in pairs: on one side of the hard drive, HBA, RAID card, or backplane, "bite" with the other on the end of the cable (Cable). As to which side is "socket" (receptacle connector, Socket connector), which side is "plug" (plug connector, plug connector), depending on the specific connector specifications.

At the beginning of SATA, the cable and connector situation is relatively simple-after all, SATA does not support port aggregation, one port corresponding to an interface connector, cable is only a single link. SAS are different: the 4-way wide link (wide link) is supported at the outset, allowing up to 4 narrow ports (narrow link) to aggregate into a wide port (wide ports), and the corresponding connector specification is developed. In this way, there are at least two SAS interface connectors, in addition to the internal and external, a variety of possible combinations to make the SAS cable type up to more than 10, so the emergence of "in the hands of the SAS cable, but can not connect the two sides of the SAS device" situation is often the case.

All kinds of SAS cables and connectors, it's too easy to dazzle people ... How many have you seen?

Therefore, it is necessary to give a detailed description of the origin and use of various SAS cable, this is the main purpose of this article.

SAS Drive Connection (top): SATA compatible

SAS first defines the interface connector for the hard drive, whose specification is SFF-8482. Because SAS is compatible with SATA, it is both backwards compatible with SATA hard drives, and the SATA cable is not connected to the SAS hard drive, the SFF-8482 spec makers are very much in the mood.

The SFF-8482 specification defines the SAS cable end socket, the pin S1-S7 is the primary port, the S8-S14 on the other side is from the port, and the power supply portion of the P1-P15 is separated from the SATA

SFF-8482 defines the dual-port (dual port) plug of the SAS hard drive, the SATA data cable is not connected, and the SFF-8482-compliant sockets (located on the SAS cable and Backplane) are free to accept SAS hard drives or SATA hard drives.

A dual-port connector (upper-middle) of a SAS hard drive is compared to a SATA hard drive connector (bottom)

As we all know, SATA hard drives have a separate SATA port and power supply, and there is a gap of approximately 2 (SATA or power) pin widths between two connectors. SAS's approach is to abort the "Partition", the two sides connected together, the second port is located in this 4~5 SATA signal pin width of the "bridge" on the back. Although the space utilization is very good, but after all also must decorate 7 signal pins, therefore from the port (secondary Port,sas②) and the main port (Primary Port,sas①) "The head" in the above physical contrast picture looks like the Vudaro and the Wu song equally obvious difference--of course, As far as width is concerned, the ability of the pin to define and transmit signals is indistinguishable.