How Do I Connect SAS and SATA HDDs to a SAS System?

PMC-Sierra was interviewed by a System Integrator about Serial Attached SCSI’s Cable and Connector Features and Uses

Author: Rachelle Trent, Product Marketing Manager
All Figures are courtesy of Molex

The challenges that System Integrators (SIs) encounter when learning how to handle new technologies, new components and especially how to make everything work together, requires research and experience. It helps them acquire the knowledge they need if they have a series of demonstrations of cables and connectors and their uses. The purpose of this article is to provide a mini-demo through the use of illustrations that are clear and easy to understand.

PMC-Sierra put the System Integrator (SI) in the interviewer’s seat and PMC-Sierra answered the questions. The SI, is a storage enclosure Original Design Manufacturer (ODM). They asked the ODM to provide a list of questions they would like to have answered about Serial Attached SCSI (SAS) system cabling and connectors. The responses follow.

Q1. We have heard that SAS is electrically compatible with Serial ATA (SATA) hard disk drives (HDDs). What about mechanical connections? Are the HDD plugs and receptacles compatible?

A1. The SAS system receptacle is compatible with both the SAS HDD plug and the SATA HDD plug, as illustrated below in Figure 1.


Figure 1: SAS System HDD Receptacles Will Accept SATA HDDs

However, a SATA printed circuit board (PCB) receptacle, will not accept a SAS HDD plug, as illustrated in Figure 2.


Figure 2: SATA PCB Receptacle Will Not Accept SAS HDDs

Q2. Our design plans will include several different mechanical configurations such as, 1) a blade configuration with multiple drives per sled, and 2) a rack configuration with multiple drives per backplane. What types of connectors are available to support these configurations?

A2. The Small Form Factor (SFF) Committee within the SAS standards working group, has specified several connectors for connecting SAS drives to a PCB. The options are right angle mount, vertical mount, panel mount and cable as shown in Figure 3 below.


Figure 3: Illustration of Four Different Connector Options to an HDD: Vertical Mount, Right Angle Mount, Panel Mount and Cable

Q3. What types of cables are available for connecting hosts to external enclosures?

A3. Two different external cables, 4-signal wide and 2-signal wide cables, have been specified in the SFF Committee as shown in Figure 4 below. The 4X signal cable and the PCB receptacle are specified in SFF-8470. The 2x signal cable and HSSDC2 dual row receptacle are specified in SFF-8424.


Figure 4: Illustration of 4X and 2X External Cables for SAS

Q4. Internal to our enclosure, it is possible that we will need to have cables connecting backplanes to controller cards. What types of cables are available for internal applications?

A4. There are several internal cables available for SAS. The first is the 1x SAS/SATA cable and connector, specified by SFF-8482, as shown in Figure 5.


Figure 5: Single Channel SAS/SATA Connector and Cable

The second cable available for internal connections within a box is a four-channel cable, specified in SFF-8484, as shown below in Figure 6.


Figure 6: Internal 4-Lane Cable, SFF-8484

In the case where a system may have a mix of the 1X SAS/SATA connectors and 4X internal connectors, special octopus cables that provide a connection from one 4X connector to four 1X connectors are available. This special octopus cable is illustrated below in Figure 7.


Figure 7: Octopus Cables Provide Connections Between 4X and 1X Receptacles

Q5. There are certainly a lot of different connector and cable options for SAS. Are there any other cables or connectors that haven’t been identified in the questions previously asked?

A5. There are several additional cables available to system integrators, such as:

1. 4x External (SFF-8470) to 4x Internal (SFF-8484), as shown in Figure 8.
2. 4x External (SFF-8470) to 1x SAS/SATA (SFF-8482), as show in Figure 9.
3. 4x Internal (SFF-8484) to 1x SAS/SATA (SFF-8482), as show in Figure 10.


Figure 8: Cable Providing Connection from 4x External (SFF-8470) to 4x Internal (SFF-8484).


Figure 9: Cable Providing Connection from 4x External (SFF-8470) to 1x SAS/SATA (SFF-8482)


Figure 10: Cable Providing Connection from 4x Internal (SFF-8484) to 1x SAS/SATA (SFF-8482)

Note: This cable also includes a plug for the side band signals

As a result of this mini-demo for the benefit of the SI, readers will aware of the mechanics and uses of SAS and SATA connectors and cables and how to connect a SAS/SATA system together.

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