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double vram cards in xfire/sli

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  • SLI
  • Graphics
Last response: in Graphics & Displays
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September 3, 2014 1:40:57 PM

ok, so i am asking here because i cant find any benchmarks/ comparisons online and i believe its a valid question. first off, i am well aware of scaling in xfire/sli and vram usage in such a setup, and i am also aware of the 'gimmick selling' as some people claim victim of, of vendors doubling vram just to charge you a few extra bucks when the gpu will never use that buffer space. my question is, does it help performance in xfire/sli? example: (and im not partial to amd but they make the best example right now) r9 270x 4gb = 256bit 4gb times 2 equals 512bit 4gb = r9 290x equals 512bit 4gb. so correct me if im wrong, but if you plan on xfire later on then the extra ram would be worth it because the scaling would be able to take advantage of the extra buffer, as opposed to just the 2gb version. please dont try to tell me to just go buy a 290x, i am aware of the issues with multi gpu setups and the advantage of having just one, this is an academic question, and i believe a valid one for someone on a budget, like me, who might not be able to just drop $500 out the gate for one (290x)and could possibly get the 2nd (270x)card later.

as a side note i specifically used the 270x as the example because, albeit a nice gpu, it has been shown in some reviews ive read to really never use that extra 2gb, maybe a bit but not enough to justify the extra 2gb(on a 4gb card).

More about : double vram cards xfire sli

September 3, 2014 1:57:29 PM

from my experience 2 lower cards never equal a single bigger card. advertised frame rates are just part of the overall equation. larger bandwidth ( 512 ) and larger buffers would be the wiser move in these recent times......... my opinions.
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September 3, 2014 2:23:20 PM

swifty_morgan said:
from my experience 2 lower cards never equal a single bigger card. advertised frame rates are just part of the overall equation. larger bandwidth ( 512 ) and larger buffers would be the wiser move in these recent times......... my opinions.


please re-read my post, i already stated what you just said, and i am aware also that under perfect conditions, optimized drivers etc, that scaling is about 1.8-1.9 with 2 cards, not the same as just one bigger one.
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September 3, 2014 2:30:48 PM

it's like trying to read a run-on sentence..........

at higher resolutions and settings it will matter a lot.......... the extra vram and the speed over one gpu vs the other. ( gpu processor speed )
an no.......... sli or xfire........... you still have the same ram as on one card............... but the extra bandwidth will help.

( i guess it's TWO 270's and ONE 290? I would still buy 1 290x. )
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September 3, 2014 2:42:11 PM

256bit is the memory bus width. You don't have extra bandwidth as each gpu uses its own vram. The same reason why cf of 4gb cards still equals 4gb vram. More vram only matters for higher res.
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September 3, 2014 2:47:11 PM

ok, sorry about the run on sentence, but once again, i stated please dont tell me to just buy the bigger card, that is not the question or the solution im looking for. so to clarify, the bus denotes the connection between the gpu and vram, correct? so yes, the 1280 stream processors on the 270x will not push the 4gb, the 2816 of the 290x will push that much vram, and yes 2560 (1280*2) is less, but not by much and since, ideally, in xfire each card is only working half as hard, thus not needing to think as much to keep up with each other, is the extra vram a viable option in xfire? it might not help it perform like that (once again) $500 290x at higher resolutions, but will it make a difference in that type of setup to where it might perform like one at a resolution, say 1440p? i dont think i would say it could hande a 4k, but i am just grasping at straws now trying to make my question clear.
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September 3, 2014 3:05:56 PM

k1114 said:
256bit is the memory bus width. You don't have extra bandwidth as each gpu uses its own vram. The same reason why cf of 4gb cards still equals 4gb vram. More vram only matters for higher res.


right, but each card has to work only half as hard, and vram also matters for effects(more frame buffer) not just texture info and meshes, like fxaa; for instance i believe in multi gpu setups there is a way to extrapolate a higher anti aliasing by the way it renders the frame between the two cards, i know i have read that before but is it still used? it could have been an nvidia trick and not aplicable to this radeon example(or a reason to swich this example to an nvidia setup......).
another example to help me understand this, if it were possible to 'hyperthread' the 290x down to 1408 streams and 2gb, yes its still better then the 270x but its only working half as hard, and shouldnt this depend more on fillrate and textel rate?
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September 3, 2014 5:19:32 PM

Oh I think I see what you were trying to get at. A 290 would have been a better example with it being closer to double the specs of a 270x. So 2x 270x 4gb would be similar performance to a 290 4gb.
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September 3, 2014 5:30:03 PM

but they're really not the same. some people look at the numbers and assume they are similar.
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September 3, 2014 11:03:43 PM

But it's similar so I said similar. I always go with throwing the spec sheet out the window and look at real world benchmarks. http://www.tweaktown.com/articles/5984/sapphire-radeon-... This shows cf 270x 2gb even beating 290x 4gb most of the time but they're not running high res and they're oced vs stock 290x. They also happened to actually run into issues you may get with cf.

I had to leave before I answered the other stuff in the last post but here goes. I don't see how any aa method will help with this issue. But there is no extra type of aa with multiple gpus.

You can't "hyperthread." I don't see how this is relevant either.

Fillrate = core clock x texture unit or rop. It's useless info imo.

I think you are overthinking the issue and complicated it with bus width, extra info and trying to give odd examples. You simply wanted to know if 2x 270x 4gb would be better than 2x 270x 2gb and if it would stack up against a 290 4gb. Ok so you can't afford a 290 right off the bat, then get a 270x with the vram you need for cf later. Playing at 1080p, 2gb is fine, the person might have just wanted to run 144fps so the extra vram is useless. In this case, the 290 just has extra vram for nothing. Only if you are higher res will getting the extra vram be useful. The single 270x 4gb will obviously not have enough power to run that by itself but you obviously are buying 4gb to cf later for that purpose; to be similar to a 290 4gb.
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September 4, 2014 1:25:58 PM


k1114 said:
I had to leave before I answered the other stuff in the last post but here goes. I don't see how any aa method will help with this issue. But there is no extra type of aa with multiple gpus.

You can't "hyperthread." I don't see how this is relevant either.

Fillrate = core clock x texture unit or rop. It's useless info imo.

I think you are overthinking the issue and complicated it with bus width, extra info and trying to give odd examples. You simply wanted to know if 2x 270x 4gb would be better than 2x 270x 2gb and if it would stack up against a 290 4gb. Ok so you can't afford a 290 right off the bat, then get a 270x with the vram you need for cf later. Playing at 1080p, 2gb is fine, the person might have just wanted to run 144fps so the extra vram is useless. In this case, the 290 just has extra vram for nothing. Only if you are higher res will getting the extra vram be useful. The single 270x 4gb will obviously not have enough power to run that by itself but you obviously are buying 4gb to cf later for that purpose; to be similar to a 290 4gb.


thank you for your input, sorry for the convolutedness of some of my questions and examples... thus thanking you for your patience as well.

as for multi gpu aa; http://www.nvidia.com/object/slizone_sliAA_howto1.html, and http://www.nvidia.com/object/quadro_sli_fsaa.html, knew i had heard somthing like that. dosent looks like it applies but knew i had read it, and any aa method adds to that frame buffer, thus vram usage, but is useless if the card cant push it, which is why most reviews limit themselves to 4x aa, at that point you are trading framerate for image quality by a good margin (depending on setup), and as you said one 270x can't push 4gb, but can 2?

yes, i am aware of no 'hyperthreading' on gpu's, thus the quotes and it was just an example referencing intel's method of splitting the core in 2 for more threads, with 5800 something cores in a 290x that would be one heck of a hack job...... odd example(back of the hand slap, ouch...)

so far you are understanding the question the best; does the extra vram help in xfire?..... would it matter or are these companies just wasting the memory chips just to earn a few extra bucks? as an example, toms hardware review of 2x r9295x2's in quadfire, it repeatedly mentions hitting the vram ceiling on a few games, so in that case, hypothetically speaking....., what would it need? that's sort of where i thought of this. i think without any real world tests (hint hint tom's) which i agree are the best, this is just a bunch of speculation and thats that.

why there are no benchmarks is a good question but i like 'pushing the envelope' of whats possible and this site has answered many questions over the last couple of years ive come to it, much respect for its methodology and mindframe, and enough so that i finally joined when i thought of this just because SOMEONE on here might have an answer thats definitive, have that type of setup and be willing to run some gpuz tests. at this point im not going to pick a best answer, but i think id like to leave it open just as a sort of sticky until a benchmark is made, but between my bad diction and your noteworthy answers what else can be said until said benchmark. thank you for your time k1114 and when i win the lottery or that rich uncle of mine that i dont know about leaves me his inheritance i will waste the money JUST to answer this and let you know, real world style
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