Question re: upgrading to dual NVidia 1080s

Blind Owl

Hi, all.

I've been running a single 8gb 1080 GTX for iRay and still find it painfully slow sometimes. So recently I ordered a 1080 TI (11gb VRAM, more CUDA cores), intending to run them in tandem.

It's my understanding that, as long as a scene will fit in either card's memory, the cards will share the load, but if a scene is too big for the GTX, the TI will have to do all the work (Y/N?).

It's also my understanding that there's no point in bridging the two cards since the iRay engine (or whatever is responsible) will handle the load-sharing (Y/N?).

I don't need the extra horsepower for anything else: the few games I still play are well within the GTX's capabilities, and I intend to make the TI my primary card.

But I know that, come Monday mornng, my computer guy will ask me if I want to bridge the two cards, and I don't know whether or not to say yes. I'm sure there are other setup considerations that I'm unaware of--my only previous experience with dual cards has been with AMD and Crossfire--so any information would be most welcome.

Thanks in advance.

ricswika

Blind Owl said:

Hi, all.

I've been running a single 8gb 1080 GTX for iRay and still find it painfully slow sometimes. So recently I ordered a 1080 TI (11gb VRAM, more CUDA cores), intending to run them in tandem.

It's my understanding that, as long as a scene will fit in either card's memory, the cards will share the load, but if a scene is too big for the GTX, the TI will have to do all the work (Y/N?).

It's also my understanding that there's no point in bridging the two cards since the iRay engine (or whatever is responsible) will handle the load-sharing (Y/N?).

I don't need the extra horsepower for anything else: the few games I still play are well within the GTX's capabilities, and I intend to make the TI my primary card.

But I know that, come Monday mornng, my computer guy will ask me if I want to bridge the two cards, and I don't know whether or not to say yes. I'm sure there are other setup considerations that I'm unaware of--my only previous experience with dual cards has been with AMD and Crossfire--so any information would be most welcome.

Thanks in advance.

I am running two 1080s. Iray doesn't use SLI. You can have him bridge the cards, but you will have to disable SLI in the NVIDIA control panel when you run Iray. You can turn it back on for games. If you don't play games, you don't need the SLI bridge.

Blind Owl

Thanks, ricswika! I seemed to remember reading something to that effect here on the forums, but couldn't find it again. 

IsaacNewton

Apparently either Iray or DS works such that the whole scene has to be fit into each card being used. So indeed, only the larger RAM card will be used if you exceed the size of your 8gb card. If this limitation is on the part of DS then presumably DAZ could redesign their render engine such that it can farm out subtasks to smaller memory cards whilst retaining the whole scene in only the largest card (if it exceeds the size of the smallest).

I have no idea how much work this would require, whether it would mean a complete rebuild of the render engine, or whether the programers were forward thinking enough to forsee the issue of multiple cards of different sizes and design the render engine's work flow such that it could be parcelled up into smaller blocks.

Perhaps someone at DAZ would like to comment on this subject.

pwiecek

Slightly OT:

You may want to do some research on Motherboard/CPU "Lanes". In short, if you don't have enough lanes, one of your cards will work at 8 bit transfer instead of 16. It is posible for your motherboard to have more lanes than the CPU. If this is the case, you have the option of upgrading the CPU at a later time.

Richard Haseltine

IsaacNewton said:

If this limitation is on the part of DS then presumably DAZ could redesign their render engine such that it can farm out subtasks to smaller memory cards whilst retaining the whole scene in only the largest card (if it exceeds the size of the smallest).

This is Iray, not anything Daz can control.

Blind Owl

IsaacNewton said:

Apparently either Iray or DS works such that the whole scene has to be fit into each card being used. So indeed, only the larger RAM card will be used if you exceed the size of your 8gb card. If this limitation is on the part of DS then presumably DAZ could redesign their render engine such that it can farm out subtasks to smaller memory cards whilst retaining the whole scene in only the largest card (if it exceeds the size of the smallest)

It seems an unconscionable waste of potential resources, doesn't it? That would suggest (to my suspicious mind, anyway) that the iRay engine is responsible. After all, NVidia is in the business of selling graphics cards...

[ edit: I see Richard Haseltine confirmed my suspicion while I was pouring a 2nd cup of coffee. Maybe there's even some technical reason for it, though I'm inclined to doubt it. ]

 

pwiecek said:

Slightly OT:

You may want to do some research on Motherboard/CPU "Lanes". In short, if you don't have enough lanes, one of your cards will work at 8 bit transfer instead of 16. It is posible for your motherboard to have more lanes than the CPU. If this is the case, you have the option of upgrading the CPU at a later time.

 

Not OT at all. My motherboard has two PCIe V3.0 slots, but I don't know if that guarantees they both have the same bandwidth. At least I'll know to ask my computer guy, and if they don't, what can be done about it (whether now or later on).

Fwiw, his technician said my existing case was awfully cramped, which I already knew--3 internal HDs, a dual hot-swappable HD bay, plus the DVD--and asked him if the customer would be OK with plugging one card into a V2 slot. Of course the answer was 'not bloody likely,' so I'll be getting a new server-type case as well.

The fun never ends.

IsaacNewton

Blind owl, you may have a point about Nvidia and Iray. It seems to be a common design philosophy these days across many product fields; don't put too many features in, they can be added later during a paid upgrade or in the next version, don't build things to last so the customer has to renew/replace on a regular basis, don't worry about bugs just call it a beta version and let world do your testing and debugging... etc etc. This might sound cynical but my experience has shown it is becoming more true in many walks of life.

A new case for your new beast of a system seems like a good idea (good opportunity to check your power supply is up to the task). I have an 850W and that was fine for two 980s, I hope it will be ok with two 1080s as they are supposed to be more efficient.

Blind Owl

The 1080 GTX is rated at 180W, the 1080 TI at 250, so I should be OK with my 850W power supply. If that isn't enough, or if it's marginal, my computer guy will let me know and I'll pass on his opinion here. (I'm extremely fortunate in having a computer guy who's both knowledgeable--most of his business is corporate network-type stuff, and he's busy all the time--and trustworthy; a rare combination indeed.) Apparently, adding a second, smaller PS is becoming more and more common, and often cheaper than buying one big hulking brute (and basically writing off the other). That's assuming the case is big enough to hold both, plus a small controller card, and still leave adequate room for cooling.

As for modern-day product design, development, and marketing, don't even get me started. I'm convinced that the invention of the electronic spreadsheet, with the subsequent rise and proliferation of MBAs and their ilk, marked the beginning of the end for civilization as we once knew it...with barcodes greasing the skids. Seriously. 

Blind Owl

In case anyone is interested and/or contemplating a similar upgrade: I'm reliably informed (at least I've always found him reliable) that an 850W PS is more than enough for my needs.

The system load is: Intel i7 on an Asus Z87A motherboard, 32gb RAM; 2 X 480gb SSDs; 2 X 1tb HDDs; 1 X 600gb HDD; 1 DVD R/W drive; 1 NVidia 1080 GTX; 1 NVidia 1080 TI.