eGPU as a second Desktop GPU

JB007

A couple of months back I got a new PC with a 4090 inside to replace my previous PC with a 3090. As such, the 3090 is now just lying around redundant. I was going to use it as a separate render machine but as it's taking me forever to sort of the spare room and get things set up - I've had a brilliant idea: Get myself a eGPU unit, pop the 3090 inside and plug it into my desktop to work alongside the 4090. Renderspeedtastic!

However. A question has cropped up :

Everywhere says eGPUs need a Thunderbolt port. I don't have one. I have USB-4 ports and plenty of them. Given Daz doesn't need fast back-and-forth bandwidth - is this a problem?

Thanks in advance

duckbomb

Yes, in my opinion it is a problem.  I know there might be others here who are more technical than me that can say DS really only needs to send the information once for render (or maybe not, I'm watering it down), because when I asked the same question this is what I was told.

I went eGPU and threw a titan card in there, and I was sorry I did.  THe thing was NOT stable at all, and would constantly fail at render time.  I don't know if it was the data transfer that was the bottleneck or something else, but I have to think it being external was a component to that.

 

I put the same components into a bigger case and pulled the GPU into the chassis and it was a night and day difference for me.

 

Just take this anecdotally, of course, my experience could be isolated, but I wish I had been warned up front.  There's just not that many credible reviews or experiences out there using eGPU with DS, from what I found (which is probably for good reason IMO).

generalgameplaying

In general they say, that 3D rendering is supposed to do a lot bidirectionally. 

Certainly USB4 is based on thunderbolt (3+-) and could in theory deliver some bandwidth (e.g. in PCIe mode, there also is USB4 2.0, not sure what you have there). Compare to your card, and ensure to calculate correctly between bits and bytes :), for a rough estimate (if the connection delivers more bandwith than your card supports on PCIex16). Of course it matters what a specific case offers.

Certainly you will have more latency, due to cable length and protocol relay, if many commands have to be transferred, and even just due to that, there could be compatibility issues (drivers might matter here too). Also "unidirectional", if the case at all, might not apply anymore, if you use two cards for rendering at the same time for one software program/process, because parts of the scene will influence each other. So logically, e.g. if some lighting conditions are calculated for a part that is rendered on one card, but influences a spot done on the other card (if that is done that way at all), then i think we have that question about "unidirectional" raised once more. 

Edit: This may be less of an issue, or near-none, if you want to use it to render for another software instance of Studio/Blender/whatever, in which case i am not sure about directionality (maybe Iray does it all on-card, if it fits into the memory). Then stability and overall performance would be the most important questions.

 

Do not take anything for granted of what i write here, because i don't have much of an idea of the internals of DAZ Studio, NVIDIA Iray (and it's capabilities for distributed resources like GPUs and CPUs and accelerators), neither do i have any experience with eGPUs. Certainly you should ensure it either is no issue for your wallet, or to get pointers about what officially is supported and how it is supposed to work, meaning reliable sources in terms of people who have tried it + official specs. (Card, Case, Connection, Cable+length, Drivers, DAZ Studio/Iray ...)

Or you're the hero to create all that data for generations to come...

outrider42

You will have to go through a lot of hassle to get it to work. The external enclosures are also not cheap. One option is to get a bigger case that handle this. A new case is still way cheaper than an enclosure.

A cheaper option is a riser cable. This connects directly to your empty pcie slot, so you do not have to deal with any USB issues. You can get a stand for the GPU. Your 4090 shouldn't be so thick that you cannot slip a small cable by it. Though some 4090s are so ridiculous I honestly can't be sure.

I have not used one personally. At least one Daz user has used riser cables to run multiple high powered GPUs successfully without a performance loss. But this is risky if you are not careful. You need to avoid mishandling.

Before you even do any of this, another thing to consider is how much power you need for two flagship GPUs. You need a really good power supply to handle a 4090 and 3090 together, and your cooling needs to be top notch, too. You would be adding roughly 350 Watts of heat to your system if you put the 3090 inside the case.

Kitsumo

The riser cable method works pretty well, but I wouldn't try to put it all in one case. Having a separate case (hopefully more elegant than mine) might give you better cooling. You'd have to get a separate power supply, but that also means you could just power down the external setup to save power when you don't need both cards.

Would I recommend it? I don't know really. It was a fun project for a few days, but if I was going to run cards like that permanently, I'd want a metal case with fans. Also, I've never even seen a 3090 in person and have no idea what kind of heat they put out.

outrider42

The 3090 is not as super power hungry as it is for gaming (Iray uses less power than demanding video games.) My Founder's 3090 peaks at 320 Watts rendering Iray, but can bounce around 310 or 300. That's high for sure, but not absurdly high compared to the 1080ti. Maybe some highly over clocked models can go higher, but Iray usually doesn't draw the full TDP.

The 4090 actually uses far less, with 4090 users reporting 284 Watts rendering Iray. That's very close to a 1080ti. Its so low compared to its TDP that I personally feel the 4000 series is not being quite fully utilized by Iray. The Iray developers have hinted this is true, as they promised to optimize Iray for the 4000 series a couple months ago. If they succeed, then the 4090 might perform faster at Iray, and it will probably use a little more power than 284 Watts.

The Founders models also have excellent coolers that fully enclose the board. They have a unique fan design, one fan is like a traditional blower, while the 2nd fan blows through the card. So heat is ejected in 2 directions, and not all heat is ejected into the case. I doubt you can get a 3090 and 4090 in one case unless the motherboard has an extra wide space between pcie slots, and of course a large case. But if it is possible, I don't think it would be a problem. Using liquid cooling could be an option here.

I think in such a situation a small mining chassis would work, allowing the cards to be spaced out. With mining basically dead, these frames are easy to find and relatively cheap. Or you can just build one, there isn't much to them.

I do think it is worth attempting. Going from a 3090 to a 4090 is kind of a modest upgrade. If you can use them both, well you would literally combine their speed, and that would be a lot faster than a 4090 alone. Iray scales very well with multiple GPUs, it is not quite perfect scaling, but at over 95% scaling it is pretty close. Often times the best upgrade is not replacing a GPU, rather it is ADDING a GPU, if that is an option. I think a lot of people don't really consider this. 

Otherwise, the best thing to do is either sell that 3090 and make some money out of it, or use it in a 2nd computer like you originally planned.

JB007

Thanks for your input, guys .. appreciate it .. Kind of puts a downer on my idea but hey-ho!

The case is a full tower so big enough to put another card in and cooling wouldn't be a problem - even with the 4090 at full tilt it barely gets above 40c due to the number of fans I've got in there  .. likewise, I overcompensated with my power supply in the build as at the time of speccing it up I wasn't sure what the draw would be within Daz .. so that wouldn't be a problem either .. but it's the lack of space on the motherboard that's the issue going with 2 cards as they would be tight against each other.

So when not batch rendering .. it kooks like the kid is going to get a top notch gaming machine .. lucky little blighter!

outrider42

If your case is that big, you could try a riser bracket. Typically these are for the people who want to show off their GPU in vertical orientation, but you might be able to find other options or possibly build your own. It is a shame that these cards are so big. This wasn't as big of a problem before the 3090. I was able to run two 1080tis, that's generations top card, together. I don't think I can get a 2nd 3090 in there, but I do have the 3060.

But yeah, the kid should be totally stoked for a 3090 gaming machine! I still game on mine from time to time and it is pretty rad to play pretty much every game totally maxxed out, and at high refresh rates. The extra VRAM is good for modding, too, if he's into that.