Connecting U.3 SSD

[Stilez]

I have read that U.3 drives are backwards compatible with U.2 connections.

I have one of those simple "shim" PCIe cards that converts the electrical connections from a PCIe slot to a U.2 slot, and I can plug in my U.2 disks just fine.
Plugged in both of my new U.3 disks and - not recognised.

That isn't what I expected.

Is there something I'm missing? Or is U.3 hardware simply not working on current FreeBSD?

 

[firesyde424]

Maybe your card isn't working? We do exactly this in a couple of servers as boot drives.

 

[HoneyBadger]

U.3 enables backwards compatibility with U.2 by sensing combinations of Host Port Type pins. Your adapter card or system might not be sending the right combination, or have the pins connected incorrectly/out of spec. See section 4.2 of the SFF-TA-1001 PDF below:

https://members.snia.org/document/dl/26900

Default/legacy U.2 should be both HPT0+HPT1 open, which will default to "Host Port Quad PCIe Single x4" but that's reliant on the adapter card respecting the spec of having the formerly-unused HPT0 left open. If it's connected to ground, the device will pull a sense on it and configure for "Host Port SFF-TA-1001 Single x4" and the two use different pinouts:

TL;DR try a new adapter card?

 

[Stilez]

I think I might have an idea of the sort of issue. But not the solution if so.

My existing U.2 drives are connected using a mix of 2 kinds of connection:

• "U.2 (SFF-8639) to SFF-8643" cable, plus
  "SFF-8643 socket to M.2 edge connector" adapter, plus
  "M.2 to PCIe" x4 card plugged direct into a PCIe 3 x8 electrical x8 physical slot
• OR:
  "U.2 (SFF-8639) to M.2 edge connector" adapter, plus
  "M.2 to PCIe" x4 card plugged direct into a PCIe 3 x8 electrical x8 physical slot

The U.2 cables and adapters I'm using are probably the same ones as in these pictures:

either:

​

plus

​

or:

​

All that Ive read about U.3 says that a U.2 drive cant work on a U.3 connection, but a U.3 drive can work on a U.2 connection. The cables and cards above both work to connect U.2 SSDs.

So I expected they should work on U.3 SSDs, as the blurb says. After all, the cards and cables provide a U.2 connection, and a U.3 drive can work backwards compatibly with a U.2 connection, says everything.

Is that assumption wrong?

Do I need different cables for "U.3 to SFF-8643" or "U.3 to M.2"? Or different adapter cards for U.3 to work with "SFF-8643 to PCIe slot" or "M.2 to PCIE slot"? Or some other SFF socket type?

 

[HoneyBadger]

Sorry for the delay @Stilez - while a U.3 device will work with a 100% spec-compliant U.2 backplane, it's entirely possible that one of those adapters or cables has grounded the HPT0 pin (S15) out of either safety or misunderstanding.

(If I'm reading the SNIA PDFs correctly, it also doesn't help at all that the original U.2/SFF-8639 has pins S14 and S16 defined as GND but the unused S15 pin wasn't set as reserved or defined OPEN - so in all likelihood all three pins are grounded, which is defined as the pin-incompatible SFF-TA-1001)

 

[Ericloewe]

An engineer at HPE stated at one point that some U.3 disks do not actually implement the required compatibility with U.2. That could be part of the problem.