PCIe splitting for GPU mining

[jØrd]

iirc Windows maxes out at 8 but dont take that as gospel. Your best option might be to buy one of those cheap expanders you linked and test it. If I had to guess i'd say their probably using cloned PLX chips (this is a thing, FTDI upset alot of people a year or two ago when their drivers started bricking devices w/ cloned / fake chips in them) but its entirely possible that their using a totally different method (as @Aibohphobia has mentioned earlier in this thread). As for daisy-chaining expanders, conceptually I guess you could think of it like a USB hub. You can get huge USB hubs w/ many ports but your still limited to a maximum speed of the USB port on the host that the hub is plugged into. Much the same applies to using PCIe expanders except PCIe signaling is much more twitchy than USB. I wouldn't put more than one expander per host PCIe slot myself. If you willing to max out at 7 PCIe cards you could probably do all this w/out having to use any PCIe expanders of any kind at all provided you get an ATX motherboard.

 

[madLyfe]

If you willing to max out at 7 PCIe cards you could probably do all this w/out having to use any PCIe expanders of any kind at all provided you get an ATX motherboard.

ya that's the problem, those are getting more expensive and harder to get.

 

[jØrd]

So what parts of this mining rig do you already own and what parts are you yet to purchase?

 

[madLyfe]

So what parts of this mining rig do you already own and what parts are you yet to purchase?

basically everything from this post: https://smallformfactor.net/forum/threads/pcie-bifurcation-motherboards.834/page-2#post-51058

the adapters, also enough risers for all my cards, 5 cards and the board(QC5000M).

 

[jØrd]

basically everything from this post: https://smallformfactor.net/forum/threads/pcie-bifurcation-motherboards.834/page-2#post-51058

the adapters, also enough risers for all my cards, 5 cards and the board(QC5000M).

So thats the stuff you already own then? (or is it the stuff your yet to purchease, you didnt really specify)


EDIT: ignore me, i was being dense

 

[jØrd]

Ok, im confused a little here.

your going to use these in your motherboard yes? And then your going to plug these into the slots provided by the first device? or is it the other way around? Is there no one on ebay (im guessing thats where your shopping given the watermarking in the images) who sells a device of this type w/ double spaced slots on it? This would eliminate the need to daisy chain, reduce the complexity, reduce the number of devices in the signal path, make troubleshooting easier, etc.

EDIT: That first device has what appears to be a SATA power input on it to provide power to the slots. Whilst I cant remember the numbers off the top of my head I do remember discussion elsewhere in this forum about using SATA - PEG adaptors to power a GPU and some question about weather the SATA connector (and the pins in it) were rated to provide enough current to safely feed a GPU at full tilt.

 

[madLyfe]

Ok, im confused a little here.

your going to use these in your motherboard yes? And then your going to plug these into the slots provided by the first device? or is it the other way around? Is there no one on ebay (im guessing thats where your shopping given the watermarking in the images) who sells a device of this type w/ double spaced slots on it? This would eliminate the need to daisy chain, reduce the complexity, reduce the number of devices in the signal path, make troubleshooting easier, etc.

yes correct. the second link, the risers, are used in regular 6-7 PCIe slotted boards so if this doesn't work I need them either way. if my cards won't fit next to reach other on the first link, which I didn't think they would, I would use the second link risers. I haven't seen any of the double spaced adapters of any size x1, x2, x3 etc on eBay.

 

[jØrd]

Your best option is probably to do some testing. Generally speaking daisychaining risers is far from ideal from a signal integrity perspective. Another possible option would be to use a device like this and just plug one card into the top slot and another into the bottom slot and ignore the middle slot. This would enable you to put two cards on each expander w/out having to daisychain another expander to make enough room. Another option would be to use more traditional PCIe flexi risers such as this in your dual slot expanders to make some space for the cards but again this would need some testing to confirm it would work. There is a whole thread here discussing which flexi risers are reliable and such. FWIW if it were me spending my own money i'd probably buy one of the triple slot expanders i linked and test that w/ two cards in it. Its the least Rube Goldberg way of going about this.

 

[madLyfe]

Your best option is probably to do some testing. Generally speaking daisychaining risers is far from ideal from a signal integrity perspective. Another possible option would be to use a device like this and just plug one card into the top slot and another into the bottom slot and ignore the middle slot. This would enable you to put two cards on each expander w/out having to daisychain another expander to make enough room. Another option would be to use more traditional PCIe flexi risers such as this in your dual slot expanders to make some space for the cards but again this would need some testing to confirm it would work. There is a whole thread here discussing which flexi risers are reliable and such. FWIW if it were me spending my own money i'd probably buy one of the triple slot expanders i linked and test that w/ two cards in it. Its the least Rube Goldberg way of going about this.

how would the GPUs fit onto those small port x3 expanders? you would have to the usb powered risers that i had show a picture of. and on the case of using a flexi riser from the expanders, those seem expensive compared to the usb powered risers talked above at only $7-$10. yes there will be testing. just busy and the risers and extenders arrive today. i have a wedding to go to so i wont be able to get to it till tomorrow or monday.

 

[jØrd]

how would the GPUs fit onto those small port x3 expanders? you would have to the usb powered risers that i had show a picture of. and on the case of using a flexi riser from the expanders, those seem expensive compared to the usb powered risers talked above at only $7-$10. yes there will be testing. just busy and the risers and extenders arrive today. i have a wedding to go to so i wont be able to get to it till tomorrow or monday.

Their not USB powered. The USB cable is being used as a physical transport but the electrical signalling being sent over the cable is the PCIe protocol, there isn't any of what most people would call USB happening at all, their just reusing an existing cable and pinout. As for how the GPU's would fit, that's simple. You have two GPU's, each GPU takes up two slots (it physically connects to a single slot but w/ the heatsink & fans on it fills up two slots worth of space, hence people tend to refer to them as "dual slot GPU's"). so you put one GPU in the top slot and another in the bottom slot, this would mean the middle slot is occluded by the first GPU but that's not going to affect performance or anything else for that matter. So, instead of having dual slot expanders w/ additional expanders plugged into them to make enough room for the GPU's you just have triple slot expanders w/ the middle slot going unused. This totally removes the need to daisy chain your expanders. As for dealing w/ putting an x16 card into an x1 slot either find an x16 version of the triple slot expander, find an x1 version w/ open back slots (this is a thing, nfi if any of these Chinese sellers make expanders in this configuration though) or just use a junior hacksaw and a needle file to open up the back of the slot or just dremel the back of the slot open whilst being careful not to dremel out the pins inside the slot.

IMO a triple slot expander and 10 minutes of effort to open the back of the slots (assuming no one sells x16 / open slot versions) is by far your best option. Anything else is a glorified Rube Goldberg machine, more likely to fail, more likely to fail in ways that are either intermittent and / or difficult to trace and harder to trouble shoot where in that component chain the failure is.

 

[Biowarejak]

EDIT: That first device has what appears to be a SATA power input on it to provide power to the slots. Whilst I cant remember the numbers off the top of my head I do remember discussion elsewhere in this forum about using SATA - PEG adaptors to power a GPU and some question about weather the SATA connector (and the pins in it) were rated to provide enough current to safely feed a GPU at full tilt.

That was my post!

 

[madLyfe]

EDIT: That first device has what appears to be a SATA power input on it to provide power to the slots. Whilst I cant remember the numbers off the top of my head I do remember discussion elsewhere in this forum about using SATA - PEG adaptors to power a GPU and some question about weather the SATA connector (and the pins in it) were rated to provide enough current to safely feed a GPU at full tilt.

TBH i didnt even notice that. its true that running six pin or molex to power them is far safer than the 50w max spec with the sata cable. if i do run the risers out of the expanders, the risers i have are powered by 6pin. so not sure if that would alleviate the issue since the card is directly into the riser and getting that power and not from the expander.

maybe something like this? PCI-E Express 1x To 16x Riser Card Ribbon Extender Extension Cable Molex Power
or this(dont see it being powered, does it need to be?) PCI-Express PCI-E 16X Riser Card Flexible Ribbon Extender Extension Cable 19cm

problem is i dont see any of those expanders as double spaced and seems all of the 1:3 port expanders are only available for shipping from china. also, in the links above, im not sure what problem im solving. though if that second link is ok and doesnt need to be powered that might be a cheap fix for the 1:2 port expander spacing issue.

EDIT:
here is a video of a guy using a 1:3 expander and this style has sata and molex power in, he is using only the sata and using the powered USB risers off of that. this doesnt mean its safe, but thats using sata for 3 cards vs the 2 cards on the 1:2 expanders i have. this video is in russian hungarian so i have no idea what he was saying before that. googles video translate for russian hungarian on yt is quite there yet lel.
1:3 PCIe expander using only sata power video

 

[jeshikat]

Posts split off into new thread since it's specific to mining instead of gaming.

 

[madLyfe]

@j0rd and @Aibohphobia i totally overlooked the fact that the pci-e 1x to 2x PCI extender was just that, PCIe -> PCI. i cant use the PCIe risers off of those PCI extenders can i? or maybe modify the backs of theme to fit a full PCIe GPU? ughhh

 

[jeshikat]

I'm not sure if they can be adapted, but definitely do not cut the connector to make the card fit. The pinout is different between PCI and PCIe.

 

[davidm71]

IIRC:
If the motherboard supports bifurcation, you need a riser with a Clock Buffer chip. AFAIK nobody has tired 'chaining' risers to split from x8 to x4/x4 etc, but whether that is possible is likely dependant on the motherboard's BIOS. You can only get as many PCIe lanes as are originally available though (e.g. from a x16 slot you can only get 16 x1 lanes).
Risers with a PLX chip should work regardless of motherboard support, and as you are not gaming compatibility problems are less likely. You can also cram as many lanes as you want onto a single physical lane. PLX chips are expensive though, so these risers will cost more.

I split 8X into x4/x4 on a non supported motherboard by hacking the bios but its not without its issues such as the occasion link speed dropping to 2.5X instead of 8X!