bifurcation 3 in 1: RTX 3090 (or Titan 2) Power & Bifurcation with x8 SSD

[Chef-009]

Q1: The 3090 pulls about 400W if I'm correct, and not 350 like Nvidia says. A PCI.e slot gives 75W so that leaves 325 Watt for 2 8-pin cables which are rated for 300W total. Does the card simply pull an extra 25 Watts from the cables? Not that an extra 12,5 Watt each matters that much but still, maybe it's 25W extra for only 1 of the 2 8-pins.
  
Q2: I want to bifurcate 1 PCI.e x16 Gen 4 slot to 1x16 running at x8 speeds and 1x8 (prefer) or 1x16 running at x8 speeds. The x16 slot for the 3090 and the x8 slot for a x8 PCI.e SSD (or x16 but I think the controllers are specifically built for x16, so by that logic it probably would be slower than x8 on x8 speeds). How does the power delivery work? Because there's 50W coming at 12V and 25W at 3V & 5V. Are both simply split in half? Or does the SSD pull that 3V&5V 25 Watt and leave 50 for the GPU? But the GPU also uses that to communicate, I think. And would the GPU just pull the missing 12V power from the 2x8 pins?

And does the splitter also use power?

And if there's only 1 x16 to 2 x16 splitters, I put in the 3090 and I only use half of 1 splitted x16 for the x8 SSD, can I still get about 15GB/s assuming the splitted x16 slot is able to handle Gen 4 at x8 speeds?
  
Q3: Can I use that x8 SSD in bifurcation, in Raid 1 with another PCI.e SSD on a m.2 pci.e motherboard slot, even if they're not the same speed or size. (Assuming it would work while using the lowest speed and size of the 2). And how would that affect real world performance? Would Smart Acces Memory still be possible without any comprimises?

 

Wonder what will happen with a so named "400W TDP" Titan RTX 2...
  
Thanks in advance!

[Electronics Wizardy]

11 minutes ago, Chef-009 said:

Q1: The 3090 pulls about 400W if I'm correct, and not 350 like Nvidia says. A PCI.e slot gives 75W so that leaves 325 Watt for 2 8-pin cables which are rated for 300W total. Does the card simply pull an extra 25 Watts from the cables? Not that an extra 12,5 Watt each matters that much but still, maybe it's 25W extra for only 1 of the 2 8-pins.

yup, those connectors can hangle much more than the 150w there rated for

 

12 minutes ago, Chef-009 said:

Q2: I want to bifurcate 1 PCI.e x16 Gen 4 slot to 1x16 running at x8 speeds and 1x8 (prefer) or 1x16 running at x8 speeds. The x16 slot for the 3090 and the x8 slot for a x8 PCI.e SSD (or x16 but I think the controllers are specifically built for x16, so by that logic it probably would be slower than x8 on x8 speeds). How does the power delivery work? Because there's 50W coming at 12V and 25W at 3V & 5V. Are both simply split in half? Or does the SSD pull that 3V&5V 25 Watt and leave 50 for the GPU? But the GPU also uses that to communicate, I think. And would the GPU just pull the missing 12V power from the 2x8 pins?

And does the splitter also use power?

The splitters often have power plugs so you need to plen them in aswell. 

 

What ssd do you want to get, most x8 ssds liek the pm1725 max out at around 25w

 

13 minutes ago, Chef-009 said:

And if there's only 1 x16 to 2 x16 splitters, I put in the 3090 and I only use half of 1 splitted x16 for the x8 SSD, can I still get about 15GB/s assuming the splitted x16 slot is able to handle Gen 4 at x8 speeds?

Yup you can get the full x8 speeds assuming your system is capable of that 

 

What motherboard and splitter are you using?

[Lord Nicoll]

15 minutes ago, Chef-009 said:

snip

I.... Don't really know what you're asking in Q2 tbh, that's... not how any of that works if I think I'm understanding what you're asking. 
For Q1 you can fully enforce power limits if you wish by not running the power limit higher, the cards are pretty strict about power draw, and generally they won't pull the full 75 watts from the slot even, they typically balance the power mostly between the power connectors. Though the offical power allowed is 150 watts per 8 pin, in actuallity they can safely supply a lot more than that with 16 AWG wires and high quality connectors. AIB cards (custom ones) have custom BIOSes on them that have higher power limits too, some are up to 400 watts, but you should be able to lower that by the 12.5% or so to take it to 350 watts if you want.

[Chef-009]

On 12/16/2020 at 4:04 AM, Electronics Wizardy said:

What ssd do you want to get, most x8 ssds liek the pm1725 max out at around 25w

I have my eyes on the PM1735 for an x8 slot and the 980 Pro for the leftover M.2 slot, but they're not set in stone.

On 12/16/2020 at 4:04 AM, Electronics Wizardy said:

The splitters often have power plugs so you need to plen them in aswell. 

Yes I've noticed that by now, on the right ones at least (https://peine-braun.net/shop/index.php?route=product/category&path=59).

The ones sold by stores don't have one afaik (https://www.density.sk/product/pcie-bifurcated-riser-cable/)

 

On 12/16/2020 at 4:04 AM, Electronics Wizardy said:

Yup you can get the full x8 speeds assuming your system is capable of that 

Yes about that. I know the slot of the PCI.e standard always stay the same, but I've seen some bifurcation risers specifically meant for PCI.e 2.0 or 3.0. Can they just as well reach 4.0 speeds or are they actually limited to 2.0 or 3.0 speeds?

 

On 12/16/2020 at 4:04 AM, Electronics Wizardy said:

What motherboard and splitter are you using?

Not sure about the motherboard yet but it will be ITX and ofcourse has to support x8x8 in the bios / eufi. The splitter will probably be one from the "right ones" link above (C_Payne) but I don't really trust it yet because of the "No waranty" basically telling me getting a working one is 50/50 and if it's DOA there are no retours or payback.

 

On 12/16/2020 at 4:05 AM, Lord Nicoll said:

I.... Don't really know what you're asking in Q2 tbh, that's... not how any of that works if I think I'm understanding what you're asking. 

Well yes, that's why I am here. I asked how power delivery works. What is the logic and distribution behind the components pulling power? That's probably a whole story by itself so if you could tell me where to start looking that would be very much appreciated. I'm not really on power constraints but still thanks for the explanation.

 

Sorry btw for the very late response, had some homework to do after you 2 replied so quickly

[Electronics Wizardy]

54 minutes ago, Chef-009 said:

I have my eyes on the PM1735 for an x8 slot and the 980 Pro for the leftover M.2 slot, but they're not set in stone.

On 12/15/2020 at 7:04 PM, Electronics Wizardy said:

Should work fine, but what is your usecase, they are likely way overkill

 

54 minutes ago, Chef-009 said:

Yes about that. I know the slot of the PCI.e standard always stay the same, but I've seen some bifurcation risers specifically meant for PCI.e 2.0 or 3.0. Can they just as well reach 4.0 speeds or are they actually limited to 2.0 or 3.0 speeds?

 

There is nothing special about gen 4 that needs different pcie cables, but runs at a higher frequency so it might not run at gen 4 speeds.

 

55 minutes ago, Chef-009 said:

Not sure about the motherboard yet but it will be ITX and ofcourse has to support x8x8 in the bios / eufi. The splitter will probably be one from the "right ones" link above (C_Payne) but I don't really trust it yet because of the "No waranty" basically telling me getting a working one is 50/50 and if it's DOA there are no retours or payback.

What cpu do you want to use? 

 

Id personally get a matx board here, but thats me.

[Chef-009]

2 hours ago, Electronics Wizardy said:

Should work fine, but what is your usecase, they are likely way overkill

I know it's way overkill, and that's pretty much the point: Pulling the absolute maximum out of the Mini-ITX form factor. Yes it will actually be build. But to be fair there will be a good amount of power required for what I'm going to be working on: Multiple complex 3D models simultaneously, virtual machines & emulation, possibly a local sever for a small business, and making very specialized games (Yes I know about the A6000, but 3090 or Titan RTX 2 seem to be the better choice).

AMD 5950X or next year's 6950X (nice) because I'm getting the feeling the 5950X is being held back by the AM4 socket, and DDR5 RAM is coming out.

mATX isn't gonna fit in the case (custom) I'm afraid.