Cables

SFF-8088 or SFF-8644: matching the cable to the port

Match the connector at both ends, SFF-8088 for Mini-SAS or SFF-8644 for Mini-SAS HD, to the ports on the array, shelf or HBA the cable will join.

Dell's manuals show which connector Compellent hardware uses. The SC100, SC120, SC280 and SCv2000 manuals describe their SAS connectors as SFF-8086/SFF-8088 compliant, the SC400 manual lists four mini-SAS HD connectors on that enclosure, and Dell's SC280 guide supports Mini-SAS HD to Mini-SAS cables of 0.5 m, 2 m, 3 m and 5 m between a controller and an SC280. Internal SAS cables for servers (SFF-8087 and SFF-8643) are on server cables, complete arrays on Dell PowerVault, and What Is JBOD? covers the expansion shelves these cables connect.

Lanes and link rates behind each connector

Both external connectors carry four SAS lanes (x4); what separates them is the generation of hardware they sit on. Broadcom's 6Gb/s SAS HBAs use Mini-SAS connectors and its 12Gb/s HBAs Mini-SAS HD, and its user guides give these link rates.

Mixed generations still link, at the lower speed: NetApp's shelf documentation notes that its 12Gb IOM12 shelf modules negotiate down to 6Gb/s when cabled to 6Gb SAS HBAs. Run length has limits of its own: Dell's support matrices cap a 12 Gbps SAS cable at 6 m on PowerVault MD34xx/38xx arrays and at 4 m on SAS-attached ME5 systems. Server cards with either connector are on SAS HBAs.

Mini SAS cable questions

What is the difference between SFF-8088 and SFF-8644?

Both are external four-lane SAS connectors. SFF-8088 is Mini-SAS, which Broadcom fits to its 6Gb/s SAS HBAs, and SFF-8644 is Mini-SAS HD, which it fits to its 12Gb/s HBAs. Each port takes only its own plug, so a cable needs the matching connector at each end: SFF-8088 at both ends between two Mini-SAS ports, SFF-8644 at both ends between two HD ports, or a hybrid cable with one of each.

Can I connect a 12Gb SAS HBA to a 6Gb JBOD?

Yes. Broadcom rates its 12Gb/s SAS HBAs for SAS link rates of 3, 6 and 12Gb/s, so the card links to an older 6Gb/s shelf at 6Gb/s, using a cable with SFF-8644 at the HBA and SFF-8088 at the shelf. Dell records the same behaviour in its PowerVault MD32xx/36xx support matrix: a Dell 12 Gbps SAS HBA auto-negotiates to 6 Gbps when connected to an MD32xx array.