I have purchased two items that I want to mate:

• A SuperMicro motherboard: X10SL7-F
• A Seagate Enterprise SAS drive: ST6000NM0034

The motherboard seems to be somewhat unique in that it has eight (8) SAS/SATA connectors connected to an LSI 2308 SAS controller. The connectors are SATA-type rather than the (apparently more common) SFF-8087 connectors.

So far, I have attempted to mate these using an adapter that has a 22-pin SFF-8482 on the female side and a pair of standard SATA data and power connectors on the male side. From what I can tell, the only pin difference between the 22-pin SFF-8482 and the 29-pin SFF-8482 is the existence of the additional 7 pins in the middle that form the second SAS lane to support SAS3. Since my motherboard can only do SAS2, I assume that these pins would not be useful anyway.

Connectors

• On the motherboard: SATA data connector (7-pin)

• On the Seagate drive: 29-pin SFF-8482

  

• On the power supply: SATA power connector (15-pin)

• On the adapter: 22-pin SFF-8482, SATA data and power

  

What doesn't work?

• None of the four Seagate drives seem to spin up at all. It's like they have no power whatsoever. Each has its own 22-pin adapter, SATA data cable, and SATA power.

What works?

• The motherboard POSTs and seems generally happy
• To test, a WD Red Pro drive, which is SATA-based, spins up and is detected on a port owned by the LSI controller AND it is powered by the standard SATA power connector from the power supply.
• The LSI controller's option BIOS appears and reports the presence of the WD drive.
• There are two SATA power cables coming from the power supply. Both have been shown to work with the WD drive.

My assumptions

• My SAS3 drive is backward compatible with SAS2
• 29-pin SFF-8482 is backward compatible with the 22-pin SFF-8482, albeit at reduced performance
• 29-pin SFF-8482's 7 center pins (on the drive) need not be connected to anything
• 22-pin SFF-8482 is pin-identical to SATA data + SATA power
• A drive with good power will spin up regardless of its data connectivity

Are any of these assumptions invalid? I'm new to SAS, so please forgive my ignorance.

Update

The entire premise of this question is faulty because the solution described in it works after all. The fault lay with my power supply, which incorrectly supplies 3.3 volts to pin 3 of its SATA power connectors. See my answer below for details.

Solution 1:

The 22-pin SFF-8482 adapter shown in the picture does work in this situation. As it turns out, my SAS hard drives have a feature known as "SAS Power Disable" according to Seagate's detailed specifications document for this drive.

According to the Wikipedia article on SATA:

The new Power Disable feature (similar to the SAS Power Disable feature) utilises Pin 3 of the SATA power connector. Some legacy power supplies that provide 3.3V power on Pin 3 would force drives with Power Disable feature to get stuck in a hard reset condition preventing them from spinning up. The problem can usually be eliminated by using a simple “Molex to SATA” power adaptor to supply power to these drives.

The fault in this case was that my Seasonic SSR-850TD power supply comes with 15-pin SATA power cables that apparently supply voltage to this pin, effectively preventing the SAS drives from spinning up. I was able to take the advice of this comment and use a Molex-to-SATA adapter to correct that problem. As a result, all of my SAS drives now spin up and are able to work with the LSI 2308 controller at 6Gbps speeds.

A document by Western Digital details this feature and potential issue.

Solution 2:

Your drive's SFF-8639 interface isn't compatible with any of the ports on your motherboard

Your Seagate ST6000NM0034 drive has a SFF-8639 12 Gbit/s SAS connector. I couldn't find an image of the actual drive's interface, but it looks like this:

If you look closely (at your drive, not this picture), you'll notice there are pins on the top and bottom of the drive's connector "blade". SATA drives only have these "golden fingers" on one side.

Wikipedia's Serial Attached SCSI article indicates the SFF-8639 is a 68-pin connector, but the SFF-8482 is only a 29 pin connector. The extra pins in the SFF-8639 interface provide additional "lanes" as shown in this image from the AnandTech.com article SFF-8639 Connector Renamed as U.2:

Note: 4GB/s is equivalent to 32Gb/s, which is the maximum throughput of the SFF-8639 interface.

According to Seagate's knowledge base article Cabling - an overview:

The SFF-8639 connector was renamed to a more consumer friendly U.2. This connector is used with some new NVMe SSDs. U.2 utilizes 4 PCIe 3.0 lanes to provide speeds much faster than the SATA interface. Since most motherboards do not have a U.2 connector on them, a M.2 to U.2, or PCIe to U.2 adapter can be used.

In other words, no adapters exist to convert the U.2 interface to a SATA-style connector, not even the SAS-2 SATA connectors on your motherboard.