SAS Cables Explained: Connector Types, Generations and Which Cable Goes Where

SAS cable types: four connectors, two generations

SAS cables are easiest to sort by their connectors, and four cover most servers and host bus adapters. Two belong to the earlier generation. SFF-8087 is what the SNIA specification calls the Serial Attached SCSI Mini SAS 4i, a wide compact internal connector. SFF-8088 is the Mini SAS 4X, its wide compact external counterpart, and its specification describes a 26-circuit shielded Mini Multilane connector. Two belong to the 12Gb/s generation: SFF-8643, popularly called the Mini-SAS HD connector system and able, its specification says, to meet the internal I/O requirements of T10 SAS-3, and SFF-8644, its external partner, which its specification says can meet the high density external I/O requirements of T10 SAS-3.

The specification titles carry the same split. The two internal connectors are titled unshielded: SFF-8087 is a Mini Multilane 4X Unshielded Connector Shell and Plug, and SFF-8643 a Mini Multilane 4/8X 12 Gb/s Unshielded Connector. The two external ones are titled shielded: SFF-8088 is a Mini Multilane 4X Shielded Connector Shell and Plug, and SFF-8644 a Mini Multilane 4/8X 12 Gb/s Shielded Cage/Connector. Only the newer pair carries 12 Gb/s in its title.

Broadcom put the change in one sentence in its SAS 9300 FAQ: the new connector for internal connection is SFF-8643, replacing SFF-8087, and for external connection SFF-8644, replacing SFF-8088. Look at the port itself rather than guessing from the card's age, because the connector beside it is what the cable has to match.

Why the SAS connectors changed at 12Gb/s

The new connectors were not a styling change. Broadcom's FAQ says the SAS standard called out the new connectors in order to reliably support the higher signalling frequencies in 12Gb/s SAS interfaces. That is why a 12Gb/s card carries Mini-SAS HD ports rather than the older Mini SAS ones, and why a cable made for an older card's connector is the wrong cable for a newer card's port.

Broadcom also expected people to mix the two generations. Its FAQ says a number of cables allow the SAS 9300 to connect to existing 6Gb/s SAS enclosures and backplanes, so current systems can benefit from the faster HBA. Upgrading the card, in other words, does not have to mean replacing the backplane.

SAS cable connector: how to tell which one you need

A SAS cable has two ends, and each needs naming before you buy. The controller end is the port on your HBA or RAID card. Broadcom's user guide for the SAS 9305-16i tells installers to use cables with an internal mini-SAS HD connector at the HBA end and the appropriate connector at the other end for the backplane or the SAS/SATA devices. Its 9400 installation guide gives the same instruction for standard 12Gb/s SAS cables.

• Controller port: SFF-8643 or SFF-8087 for an internal port; SFF-8644 or SFF-8088 for an external one.
• Far end: the connector on your backplane, or individual drive connectors through a breakout.
• Inside or outside: the internal connectors stay within the chassis; the external ones reach another box, such as an enclosure or a SAS switch.
• Power: in Broadcom's kit breakout, each SFF-8482 drive connector comes with its own power pigtail.

Breakout cables: one SAS port to four drives

Not every SAS cable runs port to port. The cable Broadcom packed with its SAS 9300 kits is a breakout: one SFF-8643 HBA connector at one end, and four individual SFF-8482 SAS disk drive connectors at the other, each including its own power pigtail and connector. It suits drives that connect directly rather than through a backplane.

SFF-8482 is a connector in its own right. Its SNIA specification defines an unshielded dual lane input/output connector for serial interface devices, backplanes and cables, and it notes multiple using generations based on performance. So the same connector name turns up on drives, on backplanes and on the ends of cables.

Because each drive end has its own power connector, count the free power connectors on your supply before you plan four drives on one port.

Broadcom did not sell a cable kit for every card. Its FAQ says there is no kit for the 9300-8e, 9300-16e and 9300-16i, because of the large variation in required cable lengths for external applications. If your card is one of those, the cable is a separate purchase.

SAS cable length: internal and external

Length matters more for SAS than most people expect. Broadcom's user guide for its 94xx MegaRAID and HBA adapters gives the maximum cable length as 1 metre (39.37 in.) for internal connections to those cards. That figure is Broadcom's for the 94xx range; we have not found the same limit stated for other cards in the documents we read.

Outside the server, Broadcom describes hybrid cables with SFF-8644 at the HBA and SFF-8088 at the far end for connecting to a SAS switch. It says the same cables will connect with legacy 6Gb/s JBODs that appear on the SAS 9300 compatibility list, so check that list before relying on one for an older enclosure. The cables come in three lengths: 1 metre (LSI00336), 2 metres (LSI00237) and 6 metres (LSI00238). Measure the run from the card to the enclosure before choosing.

Which SAS cable for which job

Put together, the documents above cover the common jobs. Each line names the cable by its two ends, which is how you should search for it.

• 12Gb/s HBA to loose drives with no backplane: SFF-8643 to four SFF-8482 connectors, with power on each drive end.
• 12Gb/s HBA to a backplane: mini-SAS HD (SFF-8643) at the HBA, and the backplane's own connector at the far end.
• 12Gb/s HBA to an older 6Gb/s backplane or enclosure: Broadcom says such cables exist; match the old connector at the far end.
• External port to a SAS switch, or to an older 6Gb/s JBOD on Broadcom's SAS 9300 compatibility list: SFF-8644 at the HBA to SFF-8088, in 1, 2 or 6 metre lengths.
• Tri-mode adapter to U.2 NVMe drives: the U.2 enabler cable, not a SAS cable (see below).

12Gb SAS cable: what the speed label means

Broadcom's 9400 guide calls them standard 12Gb/s SAS cables, with an internal Mini SAS HD connector at the controller end. The SNIA specifications for SFF-8643 and SFF-8644 both describe connectors able to meet the requirements of T10 SAS-3, and their titles call them 12 Gb/s connectors. In the documents we read, a 12Gb/s SAS cable is one built on the Mini-SAS HD connectors, and Broadcom ties the connector change to the higher signalling frequencies at 12Gb/s.

For the drives at the other end of that link, see 12Gb SAS and SAS hard drives.

SAS cable to SATA, and SAS cable vs SATA cable

Broadcom's SAS 9305-16i user guide says the 12Gb/s SAS HBA supports SATA devices and SAS devices through SFF-8643 mini-SAS HD internal connectors. Its 9400 guide uses the same standard 12Gb/s SAS cables for SAS and SATA connections: Mini SAS HD at the controller, and the appropriate connector at the other end for the backplane or the SAS/SATA devices.

That answers the SAS cable vs SATA cable question at the controller end: on these cards SATA drives connect through the same mini-SAS HD ports as SAS drives, so the cable leaving the HBA is a SAS cable whichever drives you run. The difference, if any, is at the far end, where the connector has to suit the backplane or the drive.

Two things the documents we read do not settle. We have not found a document that describes a purpose-made SAS-to-SATA fan-out cable, and we have not found one that states an SFF-8482 drive connector accepts a SATA drive. If you need either, read the cable maker's own description of the far end before buying. Our SAS vs SATA comparison covers the drives themselves.

NVMe drives need their own cables

Broadcom's 9400 cards are tri-mode storage adapters, by the guide's own title, and the guide carries a plain warning: using standard 12Gb/s SAS cables for NVMe connections might result in damage to the PCIe adapter or the drive. Broadcom's 94xx user guide says direct-attach connections to backplanes that support NVMe U.2 drives require the U.2 enabler cable, and that this cable requirement is unique to PCIe (NVMe) connections and is not required for standard SAS/SATA connections.

The same user guide describes a backplane approach whose keying prevents NVMe drives being connected with standard 12Gb/s SAS cables. If you are cabling U.2 NVMe drives, use the enabler cable the adapter maker specifies, not a SAS cable you already own.

Our English page on external SAS cables covers external connections in more depth.