SAS (Serial Attached SCSI) storage systems I/O interface and its data transmission rate and interconnect types are expanding again. SCSITA, the SCSI Trade Association, has been marketing, driving and supporting the next generation SAS 4.0 running at 24 Gbps full throughput per lane, though the actual data rate is 22.5 Gbps. The industry standards group INCITS-T10 is working with www.sffcommittee.org on developing a new higher speed SAS 4.0 specification that has many connector and cabling options. SAS 24-Gbps products will be in ramp up volume during 2017.

The SAS-4.0 24 Gbps per lane specification has three drive-to-backplane direct connection interconnect options so far. First, it has the single link drive-to-backplane connection. The detailed Drive Plug connector and its mating Drive Backplane receptacle connector specification is the SFF-8482. The contacts used in this connector are very simple and streamlined in shape, which makes a big difference in achieving optimized signal integrity performance versus the previous nine generations of SAS drive connectors like the SCA connector series. This design has high manufacturability at high volume. As a single link this drive connection has four differential electrical contact pairs—S1-S14. The other P1-P15 contacts are for power and system management functions. See SFF-8223, SFF-8323 and SFF-8523 for the different form-factor devices using these connectors. See first image set for basic plug and receptacle profiles.

The second connector type is the Multi-Link Drive Plug connector and its mating Backplane Receptacle connector covered in the SFF-8630 specification. This design supports a higher performance Hard Disk Drive (HDD) with eight differential pairs of electrical circuits. HDD higher capacity drives use too much power for datacenter use so this class of HDD devices sometimes has the disks spinning in an enclosed Helium gas chamber with less friction than earth’s atmosphere and thus saves power consumption. Some HDDs included having a SSD with it in the same 3.5-in. form-factor module. This is a cool solution, but it seems that all SSD devices and their different connectors have more of a future roadmap and much higher volume usage. See the second image set for basic plug and receptacle connector images for Multi-Link Drives.

The third connector type is the Micro-SAS Drive Plug connector and its mating Micro-SAS Backplane receptacle connector, both covered in the SFF-8486 specification. These connectors support much smaller, lower capacity and lower cost 2.5-in. SATA or SAS drives being connected to a backplane or baseboard. Check SFF-8147 for the 2.5 form-factor specification. You can put in about 120 of these small drives in a 4u storage box and a datacenter can use 50,000-100,000 boxes in many rows of racks. But these smaller capacity and size drives face much more steep cost competition from new SSD device types. So current volume usage is high but drop off usage could be severe by 2018-2019. See the third image set for basic Micro-SAS plug and receptacle connector images.

These new 3 Drive type connector options will have a lot to do with the quicker reduction of using the older Universal Drive and Backplane connector system covered in the SFF-8639 specification which could be used to support SATA, SAS and PCI-Express protocols through one large connector. One connector with too many options and extra size and cost does not work well within the current datacenter economy.

As Hard Disk Drives are replaced with Solid State Drives, the storage I/O interface of choice may differ than the traditional SAS interface. The NVMe SSD storage products are designed and implemented using other connector types. Just like the SATA storage I/O standard stopped using SATA connectors and went with SAS connectors supporting the SATA protocol, the SAS protocol may find itself going over PCIe connector and cabling types, or maybe with other network fabric connectivity. So many native I/O interfaces and their wide variety of connector types are going through convergence process as most datacenter end-users want to use just one type for simplicity and lowest cost of implementation.

A future nano-size but very high capacity SSD might only need to use a smaller connector like the USB-3.1 TYPE C.

For future designs, see SFF-8024 and SFF-8484 for overall SAS related connector mapping charts. You can also search for the T10 SAS 4.0r6 specification, as it is available although small changes are still being made.