System Administration & Network Administration
sas sata
Updated Sat, 16 Jul 2022 09:38:32 GMT

Troubleshooting SATA/SAS reverse breakout cable

For a new server build, I'm trying to connect a SAS HDD backplane (SFF-8643) to a SATA motherboard. From my research, this should be possible using reverse breakout cables.

I bought and installed two "SFF-8643 to 4x SATA" reverse breakout cables, but when I start the machine it does not recognize any of the disks (all SATA) on the backplane. As a spot test, I connected one of the disks directly to the mobo and it worked fine.

Is my understanding correct that this configuration should work? What other troubleshooting can I do?

The chassis/backplane is described as 2U 8-bay 2.5" / 3.5" HDD / SSD rackmount storage chassis with Mini-SAS HD SFF-8643 12 Gb/s interface:

The cables are described as Cable Matters Internal HD Mini SAS to SATA (SFF-8643 to 4x SATA) Reverse Breakout Cable 3.3 Feet/1mParent:


Yes this should work.

There is no visual difference in forward versus reverse breakout cables (though forward cables sometimes space the SATA connectors at multiple lengths). The cable description should specify SFF-8643 Target and 4x SATA Host. The description "SFF-8643 to 4x SATA" is insufficient as this could be SFF-8643 Host and 4x SATA Target forward breakout (notwithstanding that you say it is supposed to be a reverse breakout cable).

For troubleshooting I would see if you can borrow/buy a known good reverse breakout cable.

If that's not available, and you are handy with a multimeter or other probe you could check the wiring of the pins directly yourself. The transmit and receive pin pairs on the SATA connector will be swapped across pins 2,3 and 5,6. I was not immediately able to find a SFF-8643 pinout to be able to match up the pins for you. Also the connectors are tiny, which in my hands would result in mangling the connectors.

Comments (2)

  • +1 – Thanks for weighing in on this. I ordered new cables from a different manufacturer and surprise surprise, they work. — Oct 03, 2021 at 23:43  
  • +0 – Good to hear... maybe post a link to the good cable for future posterity. — Oct 04, 2021 at 01:42