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CrossfireX related questions + Please advise: 2x270's or 1x280 for overmodded Skyrim

Discussion in 'Graphics Cards' started by Kevmb1, Oct 18, 2013.

  1. Kevmb1 New Member

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    Hi,

    Many thanks in advance! Please read my situation before pointing out the obvious :)

    My CrossfireX related questions are:
    What are the consequences of a game using more VRAM than what's available on a discrete card setup?
    Does the answer to the above change with a CrossfireX setup?
    How much VRAM does, for instance, Crysis 3 use at Ultra settings at 1080p?

    My predicament:
    2 x 2Gb R9 270X
    OR
    1 x 3Gb R9 280X?
    Please do not advise to go with Nvidia/ SLI. This is based purely on maximizing a tight budget.



    The situation: My local PC shop has some pre-order specials on the following:

    270X: PowerColor AXR9 270X 2GBD5-DH/OC Radeon R9 270X 2G... (R 4900 for 2)
    280X: XFX Double D R9-280X-TDFD Radeon R9 280X 3GB 384-b... (R 4000)

    The obvious choice would be to go Crossfire on the 270X, but my primary reason for getting this PC is to play Skyrim with over 200 mods :laugh: .. And I've heard that over-modded Skyrim can use more than 2Gb of VRAM. And from what I've read CrossfireX doesn't sum of the VRAM of the two cards. I am going to be gaming at 1080p.
    From what I see I'll definitely be getting a better price-performance ratio overall going with the 270's, but it's not what I want if they cannot handle 'my' Skyrim. Not to mention the 280X has far superior cooling.

    Please advise! Sorry for the long post.

    I am planning on building a new gaming PC.

    i5 3470 CPU
    MSI z77-GD65 MoBO
    1Tb HDD
    120Gb Samsung EVO SSD
    XFX 80+ 750W PSU
    16Gb (8x2) 1600 DDR3 RAM
    Deepcool Neptwin CPU Cooler
    27" LED Samsung Monitor
    GPU: Will be decided on here

    The components I've mentioned above are set in stone as they are being offered on 30%-50% discounts at my local PC shop. (So I won't change them) Also, I'm from South Africa so please do not recommend me other specials or anything as I'll have to pay a butt-load of shipping and import fees just to get stuff in here :cry:

    AND NO I DO NOT RIDE MY LION TO UNIVERSITY :D
     
  2. RCoon

    RCoon Gaming Moderator Staff Member

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    If you intend to use a great deal of uncompressed texture packs, then go for the 7970/280X, because you're gonna need that VRAM.
    When your system runs out of VRAM, it dumps the rest into RAM, which lowers performance somewhat, then when RAM fills up (this never happens to me), it dumps whats left to virtual memory on your C:\ drive, which just kills your performance entirely. In short, don't cheap out on a GPU with VRAM. Most games use around 2GB, but Skyrim modded can use 4GB+ if you're going crazy potatoes with your mods.
    Oh by the way, Skyrim breaks past 60FPS, objects will start vibrating when they load and water textures will flicker, so if you dont have VSync turned on, then you might get killed by a vibrating basket of apples. It happened to me when I was using 7950 crossfire last year.
    You are correct in your research, that crossfire does not sum the VRAM between the two cards.

    When in doubt, do not Crossfire/SLI. Always go for the most powerful single GPU if you can help it.
     
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  3. Kaynar

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    my skyrim uses abit under 3GB vRAM with around 100 mods. The 280X is equal to a 7970 (which I used to have). Even the heaviest modded skyrim will run smooth with that single card, as long as you don;t crash the game from overloading the vRAM :D

    And have patience if you start crashing at random points - just unistall everything and start again! At some point it works lol!
     
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  4. Kevmb1 New Member

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    Issue solved... almost instantaneously!

    Jeez those replies were fast and extremely helpful. Thanks!
     
  5. CheezusCrust

    CheezusCrust New Member

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    2GB VRAM will be more than enough for 1920x1080, it only really hits the roof when gaming on 2560x1440. Even a heavily modded Skyrim@1080p shouldn't go past 2GB VRAM.

    I'd suggest you to get the 280x, as a single stronger GPU is almost always a better choice than 2x weaker GPU's. This is because you can get a second 280x later down the road for your rig. 3GB VRAM should also help you out later down the road if you switch to a higher resolution monitor. Remember, even though you might hit the 2GB VRAM limit, the performance loss shouldn't be noticeable.
     
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  6. Kaynar

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    Well I guess it must have been a specific issue for me then, cause the game was crashing when it reached 3072MB vRAM exactly. But yeah normally hitting the vRAM limiting is not very bad on a high end machine.
     
  7. CheezusCrust

    CheezusCrust New Member

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    If games crashed upon reaching a VRAM limit, we'd face a buttload more crashes than the ones we're getting at the moment.

    Hitting the VRAM roof merely means you'll have a small performance loss, often not noticeable.
     
  8. _larry

    _larry

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    My 7950 3gb has no problems running modded skyrim or crysis 3 on ultra. HOWEVER... Crysis 3 does struggle a bit with anything above 2xAA (trsaa? idk there are a ton of different options for aa..) 4xAA+ dips down into the 24-27fps range at parts. While 2xAA stays above a comfortable 40fps. Generally, the more AA you use the more VRAM you use. I'm not sure if this is a case of Crysis using over the 3gb of vram on my card, or if the added AA plus all the crazy physics/post processing effects are really that demanding. I'm guessing its the second. I don't think any game out there uses over 3gb of vram right now unless you crank Crysis 3 to like 24x edge AA or something ridiculous. I hear Battlefield 4 is going to use a LOT of resources with its 64-bit setting as well.

    I think 3gb of vram is perfectly acceptable at this point in time for 1080p gaming. Once games start going to 64-bit/4k resolutions, THEN we will need a TON more vram on board.
     
  9. AphexDreamer

    AphexDreamer

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    Are we sure that 2x GPU in Crossfire doesn't double the RAM?

    I've been looking into this and this guy claims Crysis 3 used 4GB of RAM 2x2048.

    Does it matter on the game?
     
  10. newconroer

    newconroer

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    No current consumer GPU architecture allows for combining VRAM across separate cards.



    For Skyrim, keep in mind that many modders also use additional graphics adjustments such as SMAA injectors and/or ENB. So while you may have enough VRAM to load and purge textures smoothly, your overall performance is still under further strain due to higher resolution textures, increased LOD, better shadows etcetc. Couple that with ENB injector for example, and you're now trying to decide which mods to sacrifice to retain good performance.

    I'd rather have a faster GPU, than one with additional VRAM.
     
  11. manofthem

    manofthem WCG-TPU Team All-Star!

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    Indeed sure. In the ss there, msi AB reads over 3gb of vram usage because that's how the program (msi AB, and gpuz I believe) see it, but it doesn't effectively double usable vram. What that ss means is that each card was using ~1.7ish gb max out of 2gb available of vram because each card is using is own vram.

    (similar to a raid1 setup where 2x 1tb hdds only yield 1tb of usable storage, as each hdd is mirrored with the other one. While there's technically 2tb of actual hard disk, there's only 1tb of data storage )

    Despite how msi AB displays it, 2 cards with 2gb each will only yield 2gb of usable vram; 2 cards of 3gb will yield 3gb.
     
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  12. AphexDreamer

    AphexDreamer

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    So like RAID 0 is the RAM effectively faster? If not Is Crossfire even worth it? NO RAM boost of any kind just computation boost, its like losing 75% of the second card.
     
  13. manofthem

    manofthem WCG-TPU Team All-Star!

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    The ram is not faster. But you are using both cards at the same time rendering frames instead of 1, so your fps can effectively double, given the game/driver support. In that sense, it's like raid0 where there's the performance boost, but vram wise, it's not like RAID0 . the increase in performance comes from 2 gpus rendering rather than just one, not the amount of vram

    As a long time crossfire user, it's almost always worth it imo. I always start with a single card and then add another. In the vast majority of games, there's a performance boost, though not guaranteed and not always near perfect scaling.
     
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  14. AphexDreamer

    AphexDreamer

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    My bitterness towards it comes from the fact that more and more games are becoming RAM demanding, including 2GB or 3GB graphical options for things like higher res textures which makes it seem like no amount of Graphics Power is going to aid in your RAM cap. So you'd think they'd come up with a way for Crossfire to be more useful in that area and have it stack RAM with multiple cards. I was excited with the prospect of adding a second 270x but am now contemplating selling the one I have to buy a 280x with 3GB of RAM instead.
     
  15. manofthem

    manofthem WCG-TPU Team All-Star!

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    I really wouldn't be that bitter about it. The deal is that usually cards run out of power before vram. When I had my 7970s, I don't think I ever hit a game that went over the 3gb mark, and currently with my 4gb of vram, I still haven't noticed anything that goes over the 3gb. I've played BF4 maxed at 2560.1440 and I never use up all 3gb let alone 4. I only dabbled in Skyrim with some mods and though i hear that people use a lot of vram in that, I never hit my limit.


    If I recall correctly, when using crossfire, each cards alternates the frame being rendered; the cards do not render the same frame. Thus, each card uses its vram independently and really is unable to stack the total usable. Vram usage depends a lot on resolution and pretty much 2gb is good for 1080p gaming, though I'm sure there're the exceptions.


    A single more powerful card is always preferable though, so that's not a bad idea if you wish to sell what you have and go for a better card. Keep in mind however, that by doing that, the trade off is less performance but you'll have a little more vram for those isolated instances when you may run into it.
     
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  16. The Von Matrices

    The Von Matrices

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    The current paradigm with Crossfire and SLI is alternate frame rendering, where each GPU alternates rendering each frame. Since the frames being generated by each GPU are so similar, you need the same data in the memory of each GPU. You conceivably could have only one copy of data across all GPUs, but that would require communication over the PCIe bus, which is 20x slower than local memory (~16GB/s versus ~320GB/s) and higher latency.

    If split screen rendering became common (e.g. one GPU renders the top half of the screen and the other renders the bottom half), then there could be some RAM savings since each GPU would be using different geometry and textures. It wouldn't scale 100% with each additional GPU, but the effective memory capacity would be greater than one card. Some games do use split screen rendering, but the idea of having separate framebuffers on each GPU is something that hasn't been done yet due to the complexity of the algorithm needed. Since most GPUs don't reach their memory limits, and adding more memory to a card is cheaper than writing and perfecting the software algorithm, I don't see it occurring any time soon.
     
  17. MxPhenom 216

    MxPhenom 216 Corsair Fanboy

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    I wouldnt do CF at all for Skyrim. Scaling is pretty bad.

    I would get a single R9 290 non x.
     
  18. AphexDreamer

    AphexDreamer

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    Well I can't be sure if I am going over 2GB or not since GPUz won't correctly tell me. But I thought the Dedicated Memory and Dynamic memory got switched, if that is the case then I am going ove 2GB quite frequently. If not then It means I suffer from computational needs rather than lack of RAM. I'll reach a better conclusion before deciding.

    I suppose Crossfire won't ever really need to stack RAM because they will probably just shove more and more RAM on each card. But probably in the far future though, the option to change Crossfire modes will come into play. They did eventually get to hybrid.
     
  19. Lightbulbie

    Lightbulbie

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    I don't use like, 100+ mods. (I use about 12-15 total) But 5-7 are the really high-res texture packs. My VRAM will grind up to 1.5/2Gb of usage. This includes maxed 1080p settings. (GTX 660 OC 2GB)

    If you're really going to pack on the mods, get a 3GB for a safe overhead.
     
  20. newconroer

    newconroer

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    I do not know if you missed my first post above, but I touch on the fact that textures processing and loading requires all aspects of the GPU to be efficient, not just a large VRAM capacity. The fact that VRAM is exclusive per card, does not mean the GPU's horse power becomes irrelevant.


    Rivatuner Statistics (bundled with MSI Afterburner) can be setup to show you how much memory you are using per GPU.


    As for whether or not to use Crossfire? As a technology both Crossfire and SLI scale very well on GPUs from the last several years and the majority of games support it where possible. The only downside to Crossfire (as opposed to SLI) is that you cannot use it in Windowed mode. That's a big deal to some people, and it's not to others - but it's about the only significant point to consider when deciding. My rule of thumb is that when a new flagship GPU launches, either buy the little brother version, or buy the flagship from last generation. Then if you find it's not enough, wait a bit and buy another one.
     
  21. AphexDreamer

    AphexDreamer

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    Oh I have MSI AB running it seems to tell me. I'll play a few games and check it out.
     
  22. URBAN303

    URBAN303

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    False ! VRam's are added in Windows : or explain it > [see screens captures] do not thank me it was a pleasure;)

    * Eurotruck Simulator 2 , on 3840x1024 with CF 7850OC 2GB (each) ^^ -- 2013 --
    -> https://dl.dropboxusercontent.com/u/30314017/ETS2-CF7850OC2GB.JPG


    In crossfire mode, each card is added or combined in the primary adapter; if you have 2 or 3 video card then the main adapter contains the sum of memory and other parameters of each card ... (rop, tmu, shaders, cu ....) and Hypermemory Technology can added "dynamic memory" shared via your RAM System installed ^^ (go to the link below and jump to table) :
    -> https://support.sapphiretech.com/presentation/article/article_faq.aspx
     
    Last edited: Jul 30, 2014
  23. Lightbulbie

    Lightbulbie

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    You're a month late..
     
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  24. URBAN303

    URBAN303

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    Sorry, I was entitled to holiday;)

    edit : it can always serve as a way ^^
    2*7850 = more perfs than 280X , CF7850 have an advantage of 32 ROP's ....
    so 2*7870 or 2*270x = advantage of 32rop + 32tmu = excellent combination ! ^^
    but CF is not always perfectly beneficial. that is why it is more interesting to have two powerful enough cards.
    The difference between cf7850 & r9 290x it is just and only a benefit for 48tmu for r9 290X and 816 Shaders and 12 compute units ; nothing short of extraordinary in either ... we need to know ;)
    This is why 290x mono-processor is more interesting than CF 280X; but so great either ^^
    but CF 7850OC/7870/270X/280X not much to envy 290x;)
    so little that costs 290x is not justified for me;)
     
    Last edited: Jul 30, 2014
  25. Andrew LB

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    I'm using about 65 mods and i'm not sure how either graphic card choice is going to be able to run graphics like this since it manages to b*tch slap my GTX 780 Ti pretty good. Low of about 45fps but typically just under 60.

    Whatever your decision, i think you'll be happiest with a single GPU solution. CF/SLI is typically more trouble than it's worth IMO.
     

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