Powering a PCI-E SAS expander without a PCI-E slot? Theoretically possible to make an adapter?

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TheBloke

Active Member
Feb 23, 2017
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Hi all

I'm thinking of adding at least one SAS expander to my setup, as I am currently using 4 x LSI cards - and therefore 4 x PCI-E 2.0 slots - to run 28 x 2TB SATA3 drives. I know that I can put more drives on fewer cards without losing performance, but as I have a low-profile case I can't use 4-port LSI cards as they're all full-height. Unless I cut a hole in my chassis roof which stupid as it sounds I may actually consider...

I'd much rather get an expander or two. But then my problem is that most of the cheap SAS expanders I can find on eBay require a PCI-E slot for power. Which rather defeats the object; my aim is to free up PCI-E slots, not use them to power SAS expanders! I know it's possible I could get one expander that would free up two of my slots, so that would still be a net gain. But I would really prefer to have access to all the freed slots, not have them 'wasted' providing only power.

I'd also like more flexibility in where I can physically locate any expander.

There are expanders that take 4-pin molex power, and that would be perfect. But so far I can't find any cheap ones available to the UK. The few that I have found (one IBM, one Chenbro) are much more expensive than the ubiquitous HP expanders flooding eBay: I can get an HP 3GB/s expander for £25, whereas an IBM or Chenbro is £100+.

So I was wondering if there was any way to make an adapter that would power a PCI-E card? Like maybe I could rip a PCI-E slot off an old motherboard, and solder up some wires to a 4-pin Molex plug somehow? :)

I am sure it's going to work out to be far more complicated than that.. for one thing the soldering is probably going to be hard, but maybe there's an even bigger problem. It occurred to me that maybe it can't work because it will expect more than just 12V power? Maybe it actually has to talk a protocol to the motherboard, even when it only needs power? I was hoping that I'd find that some of the PCI-E pins are directly wired to 12V / 5V / 3.3V (I haven't yet checked what voltages are sent), but maybe it's not nearly that simple.

The more I think about it the more I think there's a million reasons why this could never work, but I'd be grateful if anyone has any thoughts? At the least a firm "you're crazy, that's impossible" would enable me to move on to weighing up the other options :)

Thanks
 

Evan

Well-Known Member
Jan 6, 2016
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Pretty much what @RyC said, it only needs the power. The OEM's just use the PCIe slot as it serves the dual purpose of power and a place to mount the hardware.
(Atleast that was the case on the old versions, not tried on the current ones but I have some out of a server if you need close up photos etc to see what pins are active)
 
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TheBloke

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Feb 23, 2017
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Oh wow awesome! Thanks so much guys. I'd hoped there might be some kind of pre-made adapter but I couldn't find anything in searching until I put in 'mining'

Available in the UK as well, going to get one right now. Thanks so much!
 

TheBloke

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Actually I might have just found another solution as well - looks a similar concept, but from IBM!

When I went to search for SAS Expander again this morning, this was one of the first listings on eBay:

IBM 43V7067 Right Angle PCIe x8 SAS Expander Riser Card w/ USB x3550 x3650 M2 M3


I can't find any more info on this at the moment, but it rather looks like a USB socket to power a x8 slot? Unless the USB-A socket is an output. But the fact they have 'SAS Expander' in the title rather suggests to me this is meant for exactly what I want it for, powering a SAS expander separately.

EDIT: Actually, more searching has found a couple of parts listings that say 'With USB Reader' which suggests it is an input. So scratch that one! No worries anyway, it's more expensive than the mining adapters
 
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ttabbal

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Mar 10, 2016
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You mentioned you are looking at 3Gb/s expanders. Note that those usually are limited to 2TB drives. You may already know and be fine with it, just making sure.
 
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TheBloke

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You mentioned you are looking at 3Gb/s expanders. Note that those usually are limited to 2TB drives. You may already know and be fine with it, just making sure.
Oh, thanks for the tip. I didn't know that actually. As it happens, it's no problem - all my drives are exactly 2TB. I have 27 x 2TB 7200rpm SATA3 drives. Of course a 6GB expander would be the ideal, but I am expecting that SATA2 will be no bottleneck for the spinners.

Good to know for the future re expanding capacity though, thanks. Though by the time I could think about replacing with larger drives, hopefully 6GB will be cheap and available!
 

TheBloke

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Just wanted to close off the thread with what is, for me, the rarest of situations: an unmitigated, un-qualified, complete and total first time success :)



My eBay-sourced HP SAS expander powers up from the mining adapter fine, connects to the HBA fine, sees all my disks fine and, most importantly, negotiates SATA2 3GB/s, indicating it's already been upgraded to one of the later firmwares and therefore I hopefully won't have to go through a messy hacking procedure to get the FW updated without having the usually-required HP HBA.

Having been deep in a spiral of seemingly never-ending upgrades and re-upgrades for more than 6 weeks, I can attest that - at least for the cheap and often slightly suspect gear that is usually all I can find and afford - such success is definitely not to be taken for granted :) And I didn't even have to Dremel anything!

Thanks again for putting me in the right direction, all :)

(Of course, the reason I need this at all is so I can free up a PCI-E slot in which I plan to install a Full Height PCI-E SSD.. into my 2U low-profile case. Thus requiring what will probably be my biggest hack-job yet.. ;) Where's that Dremel gone?)
 

Daniel46542

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Sep 13, 2020
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I haven't got this to work yet. At first I thought my expander was DOA. I tried using another computer for the expander and it works! However, I don't have a pci-e slot to spare. I bought an soc with only 1 connector for the sas controller.
I already tried pci-e risers before and after find the expander works
The expander works while connected to the riser only when the riser is plugged into the motherboard pci-e slot
I've tried one riser with 4-pin molex
I've tried another riser with 4-pin and/or sata power connecter
maybe if there is someway to connect the pci-e port on the rise to the psu?
one riser is soldered to the x1 pci-e connector while the other has a "usb" looking port like the one in the picture above
One workaround is to by a cheap motherboard and use another power supply which seems a waste.
I may just buy another soc, or buy the cheapest, lowest power version of my main computer to aid troubleshooting as the soc isn't as conservative as i was lead to believe
 

ari2asem

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Dec 26, 2018
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intel and chenbro sas expanders don't need pci-e power. only hp expander needs pci-e power.

intel and chenbro expanders need 4pin molex power connector. but intel expander also works with pci-e power. so, intel expander works either with 4pin molex power or with pci-e power.

my favourite choice is chenbro expander.
it has also 2 external sff-8088 ports for daisy chainning and small fan on chipset cooling block. and expanders in general get always hot, even in idle.

or you need air flow over your expander
 

Daniel46542

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Sep 13, 2020
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Thank you for the fast reply. I should have said I'm using the HP 468406-B21 24 Bay SAS Expander
It does get hot, slowly building up, but not without being connected to the motherboard or riser connected to motherboard
I've ordered another riser card that accepts 6-pin pci-e power like on a graphics card, hopefully this will be it
I'll update