10Gb SFP pairs over short SATA (6Gb)

[glenenglish]

Anyone tried this ?
10Gb SFP pairs over short SATA3 ?
SFPs are such a board hog. And often, with dirt and dust, you want the SFPs which are open to the elements, to be environmentally isolated from your mainboard....
Samtec have some nice cables
https://www.samtec.com/products/fsfp#packaging
An SFP with a cable hanging out the back to connect on a SATA like connector to your mainboard
But, thought since SATA3 6 Gbps works down a meter of SATA3 cable, maybe 10Gb will work down at 6"......
Should work....
acccording to the spec, a 1m cable can have up to 6dB loss at 4.5 GHz.... so at 15cm, that will work.
Table 36 – Internal cable / connector measurement parameter and requirements
and max 20ps skew.
There are even better than standard connectors (apart from the usual Molex) from AMphenol
https://cdn.amphenol-cs.com/media/wysiwyg/files/documentation/datasheet/ssio/ssio_sata.pdf

[scottapotamas]

I've previously abused a SATA breakout on a devkit to claw back some transceivers and they worked fine at ~8Gb with some unknown 20cm cables that came bundled with an old motherboard.

Recently used a SFF-8611 (aka Occulink 4i) connector/cable for some internal high-speed connections and had no issues - they're typically rated (slightly questionably) for PCIe4.
Not as cost optimised as SATA but still cheaper than the cables for Samtec Razorbeam or QStrip families etc.

Throwing another possible option onto the pile (no personal experience) -  the connector/cable ecosystem for SAS backplanes and HBA cards i.e. miniSAS internal

[glenenglish]

thanks Scott, I will investigate miniSAS.

[asmi]

if you want to use cheap cable, use USB-C cable. It's got 4 differential pairs which you can use however you like, each pair is typically rated to at least 10 Gbps (for USB 3.2x2). If that's not enough, you can use Thunderbolt 4 cable, which is rated for 20 Gbps per link if my memory serves me. Both options are much cheaper than specialized solutions with custom cables. ...just make sure nothing blows up on both sides if your user connects a real USB-C device or a USB-C power supply to your connector, because it will 100% happen sooner or later...

[nctnico]

I second asmi's suggestion. I have used USB-C connectors + cables to bring out PCIe to a daughterboard.

[glenenglish]

mmm. I've only got to go 15cm.  I measured some SATA cables yesterday, on the 20 gig ZVM VNA... they'll be just fine .. if they are not bent around any sharp corners.... They are just awful if tightly bent.. not unexpected....

The USB-C idea with four pairs is a good one -  2 lane PCIe  between FPGA boards springs to mind.....
And quite a compact connector.
Yeah you guys are right, the USB-C might be a better option.
should be able to buy 15cm jumpers...
The spec says 6dB loss typical for a meter of cable at 10 Gbps.   I've encounted problems with transceiver configuration when there wasnt enough loss...
with the USBC 24 pin connector, with two pair used, there would be enough pins to send power, I2C control, and two channel status lines... excellent...  with two pair, might even be able to drive two SFPs....
great idea Asmi.

[asmi]

I've encounted problems with transceiver configuration when there wasnt enough loss...

You can always reduce pre-emphasis if you channel is "too good". Or tune receiver. Or both. This is a GOOD problem to have.

with the USBC 24 pin connector, with two pair used, there would be enough pins to send power, I2C control, and two channel status lines... excellent...  with two pair, might even be able to drive two SFPs....
great idea Asmi.

Make sure you add circuitry to detect cable orientation and a cross-switch in case orientation is not matching on both sides. All of that exists as a ready-made COTS ICs. Or add some other provision to deal with that potential problem.
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There is also a fifth differential pair, but it's only rated for USB 2.0 speeds (480 Mbps).

[langwadt]

how about HDMI(mini) or displayport(mini) ?

[asmi]

how about HDMI(mini) or displayport(mini) ?

These are also good options, but I personally prefer USB-C cables as they are more flexible, and USB-C connector is smaller than HDMI/DP. For min-versions cables are not as readily available as USB-C ones.