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Will Corsair GS800 PSU be sufficient to power 2x Sapphire 7970 Vapor-X 3GB GHz Edition crossfire

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April 14, 2013 12:34:25 AM

Hi,

I am building my new photo editing/gaming PC. I have 2x Sapphire HD7970 GHz Ed Vapor-x 3GB graphics cards in xfire and for PSU I've bought Corsair GS800. So my question is will this 800W PSU be sufficient to power my system effortlessly without any issues? The AMD official site states that a minimum of 850W PSU is recommended. Please suggest if I should use this PSU or try to exchange it for a better one with higher wattage?

I am also concerned because my CPU/mobo combo are also power hungry. I have a 3930K processor and Asus P9X79 Deluxe motherboard. Let me give you my whole system configuration, so that it is easier for you guys to recommend the best PSU for this build.

CPU: Intel i7 3930k
Cooler: Corsair H100i
Motherbboard: Asus P9X79 Deluxe
RAM: 4x 8GB (total 32 GB) GSkill Ripjaws Z 1600
SSD: 120 GB Kingston HyperX 3K as boot drive
HDD: WD Caviar Green 2TB x2 (Total 4TB)
ODD: LG Blu-ray writer
Graphics Card: 2X Sapphire Radeon HD7970 GHz Edition 3GB Vapor-X in xfire
Sound Card: ASUS Xonar Essence-ST
Monitor: Dell Ultrasharp U2713HM 27" IPS monitor 2560x1440
PSU: Corsair GS800 (This is my biggest concern????????)
Cabinet: Cooler Master COSMOS II
KB: Corsair K90
Mouse: Corsair M90
Speaker: Logitech Z906 5.1

So, please help me out here with the PSU I've chosen here guys. I am worried with that part. :(  Please let me know if you need any other information to make the best decision. And please reply soon as I don't want to delay if I've to exchange my PSU.

N.B. I've found this on Guru3d which raises my concerns even more. It says -

"Here is Guru3D's power supply recommendation:

Radeon HD 7970 - On your average system the card requires you to have a 550 Watt power supply unit.
Radeon HD 7970 Crossfire - On your average system the cards require you to have a 750 Watt power supply unit as minimum.
If you are going to overclock GPU or processor, then we do recommend you purchase something with some more stamina."


So should I not keep a reasonable buffer amount of power available at my disposal ?

Thanks,
Susmit
April 14, 2013 12:39:17 AM

Yes, it will be fine. Give me a sec and I'll do some maths for you.
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April 14, 2013 12:50:41 AM

slicedtoad said:
Yes, it will be fine. Give me a sec and I'll do some maths for you.


Okay.. waiting for that. Thanks in advance slicedtoad.
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April 14, 2013 12:59:30 AM



@bigcyso1, so basically you are recommending a 80 PLUS GOLD certified PSU between 850-1000W .. I think this GS800 is 80 PLUS Bronze ..

oops.. i see that u've removed all your suggestions and kept this one only! may i know why? is this pc power 950 silver the best among them? :-o
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April 14, 2013 1:02:06 AM

Also there will be 6 120 fans, 1 140 fan and 1 or 2 200/230 fans.. so they will also consume some power..
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April 14, 2013 1:02:50 AM

fatboyslim said:


@bigcyso1, so basically you are recommending a 80 PLUS GOLD certified PSU between 850-1000W .. I think this GS800 is 80 PLUS Bronze ..
Yeah because i don't think the GS800 will cut it better to be safe then sorry imo.

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April 14, 2013 1:06:23 AM

-7970 = 270W
-i7 3930k @ 5GHz + mobo = ~250W (this is a slightly hard to measure but should be a slightly high figure if anything)
-Everything else: 20-30W (but not on the 12v lines, so they don't matter)

270*2+250 = 790W on the 12v lines.

PSU: 780W on the 12v rail

So that's a bit close to the limit actually, but it should will work fine. Just don't OC you cpu to 5GHz, lol. ~4.5Ghz will give you far more headroom (that i7 uses about 150W less power at stock clocks so interpolate between 100W and 250W to get a rough estimate of an overclock between 3.2GHz and 5GHZ).

If you decided to buy a different one I wouldn't blame you, but if it were my system, I'd stick with it.
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April 14, 2013 1:08:05 AM

fatboyslim said:


@bigcyso1, so basically you are recommending a 80 PLUS GOLD certified PSU between 850-1000W .. I think this GS800 is 80 PLUS Bronze ..

oops.. i see that u've removed all your suggestions and kept this one only! may i know why? is this pc power 950 silver the best among them? :-o
It's the cheapest best deal among them.
;) 

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April 14, 2013 1:12:47 AM

slicedtoad said:
-7970 = 270W
-i7 3930k @ 5GHz + mobo = ~250W (this is a slightly hard to measure but should be a slightly high figure if anything)
-Everything else: 20-30W (but not on the 12v lines, so they don't matter)

270*2+250 = 790W on the 12v lines.

PSU: 780W on the 12v rail

So that's a bit close to the limit actually, but it should will work fine. Just don't OC you cpu to 5GHz, lol. ~4.5Ghz will give you far more headroom (that i7 uses about 150W less power at stock clocks so interpolate between 100W and 250W to get a rough estimate of an overclock between 3.2GHz and 5GHZ).

If you decided to buy a different one I wouldn't blame you, but if it were my system, I'd stick with it.


:ouch:  my goodness .. that's 10W more than what this psu delivers over the +12V rails ... :(  that is depressing enough .. would not that lessen the PSU longevity? all the time running above and beyond its normal throughput? And if gpu and cpu are overclocked then it can turn its back on me!!! :??: 
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April 14, 2013 1:18:35 AM

bigcyco1 said:
fatboyslim said:


@bigcyso1, so basically you are recommending a 80 PLUS GOLD certified PSU between 850-1000W .. I think this GS800 is 80 PLUS Bronze ..

oops.. i see that u've removed all your suggestions and kept this one only! may i know why? is this pc power 950 silver the best among them? :-o
It's the cheapest best deal among them.
;) 



okay .. i see ..
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April 14, 2013 1:29:17 AM

good. The guru3d one is the v2 and is better. It has 792W on the 12v rail and is bronze rated.

fatboyslim said:
:ouch:  my goodness .. that's 10W more than what this psu delivers over the +12V rails ... :(  that is depressing enough .. would not that lessen the PSU longevity? all the time running above and beyond its normal throughput? And if gpu and cpu are overclocked then it can turn its back on me!!! :??: 

Are you an awesome OCer that needs 5GHz? Otherwise, you are no where near that limit.
And ocing your gpus is not really nescessary. 2 7970s will run that monitor fine.

A PSU should never be run over it's limit but that should be easy to avoid. Running it close to it's limit will make it run hotter and will likely reduce it's life time (could still be a long time). And it still has a 3 year warranty that won't be voided by running it close to load.

Also, those are max load power figures. They usually won't be that high which means that most of the time your PSU will be running at only a few hundred watts.

edit:
but if you're worried, the one bigcyco mentioned would be a fine upgrade. Might even save you a few dollars in electricity. And it should be a bit quieter.
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April 14, 2013 1:38:29 AM

slicedtoad said:
good. The guru3d one is the v2 and is better. It has 792W on the 12v rail and is bronze rated.

fatboyslim said:
:ouch:  my goodness .. that's 10W more than what this psu delivers over the +12V rails ... :(  that is depressing enough .. would not that lessen the PSU longevity? all the time running above and beyond its normal throughput? And if gpu and cpu are overclocked then it can turn its back on me!!! :??: 

Are you an awesome OCer that needs 5GHz? Otherwise, you are no where near that limit.
And ocing your gpus is not really nescessary. 2 7970s will run that monitor fine.

A PSU should never be run over it's limit but that should be easy to avoid. Running it close to it's limit will make it run hotter and will likely reduce it's life time (could still be a long time). And it still has a 3 year warranty that won't be voided by running it close to load.

Also, those are max load power figures. They usually won't be that high which means that most of the time your PSU will be running at only a few hundred watts.


no.. I would not be pushing my cpu to 5ghz mark .. may be @max around 4-4.3 .. so it seems 800w will cut it but then again there IS a chance that it might be a bottleneck at times probably .. so it is safer and better to opt for something with a higher wattage .. something between 900-1000 W .. am I right?? just 2 be on the safer side .. ????
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April 14, 2013 1:40:36 AM

slicedtoad said:
good. The guru3d one is the v2 and is better. It has 792W on the 12v rail and is bronze rated.

fatboyslim said:
:ouch:  my goodness .. that's 10W more than what this psu delivers over the +12V rails ... :(  that is depressing enough .. would not that lessen the PSU longevity? all the time running above and beyond its normal throughput? And if gpu and cpu are overclocked then it can turn its back on me!!! :??: 

Are you an awesome OCer that needs 5GHz? Otherwise, you are no where near that limit.
And ocing your gpus is not really nescessary. 2 7970s will run that monitor fine.

A PSU should never be run over it's limit but that should be easy to avoid. Running it close to it's limit will make it run hotter and will likely reduce it's life time (could still be a long time). And it still has a 3 year warranty that won't be voided by running it close to load.

Also, those are max load power figures. They usually won't be that high which means that most of the time your PSU will be running at only a few hundred watts.

edit:
but if you're worried, the one bigcyco mentioned would be a fine upgrade. Might even save you a few dollars in electricity. And it should be a bit quieter.


yeah .. okay that is what i feel .. a bit worried .. after all all these are expensive components and its better not to risk any one of them .. :( 
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April 14, 2013 1:55:01 AM

For your own peace of mind, it could easily be worth it, it's up to you.

But at 4.3 GHz, you won't be at the limit. You'd even have some gpu oc headroom. That said, if I were building a computer exactly like yours I would have picked a slightly higher wattage PSU. If I was upgrading my hypothetical computer with a second 7970, I wouldn't change the PSU.

Since your PSU is still within the easy return period, swapping it would be fine but not completely necessary.
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April 14, 2013 2:11:25 AM

slicedtoad said:
For your own peace of mind, it could easily be worth it, it's up to you.

But at 4.3 GHz, you won't be at the limit. You'd even have some gpu oc headroom. That said, if I were building a computer exactly like yours I would have picked a slightly higher wattage PSU. If I was upgrading my hypothetical computer with a second 7970, I wouldn't change the PSU.

Since your PSU is still within the easy return period, swapping it would be fine but not completely necessary.


hmm .. got your point man .. so its better i swap it with a higher wattage one .. but can you guys recommend me the best option among Corsair/Seasonic/Coolermaster in that wattage range?? dont give too many options please :)  makes it harder to choose .. other manufacturers likenzxt/pc poweretc are not available here in india that easily ..
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April 14, 2013 2:25:38 AM

I'm not sure what store you use but between flipcart and theitdepot the best I can find are these
Antec HCG-900 for 9700 rs
and
Corsair TX850 for 8240 rs

You could go higher if you wanted but the prices are quite inflated compared to NA. The Antec will give you all the power you need plus some nice headroom. The Corsair won't have quite as much headroom but it will still work fine and should allow for everything to be oced a decent amount.
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April 14, 2013 5:03:23 AM

Anything bronze rated and above by Seasonic, Corsair, Antec, PC P&C, XFX, Thermaltake, EVGA, NZXT, OCZ, Zalman, Cooler Master or Enermax at 900W or higher is fine. Pick whichever is cheapest at wherever you shop or whichever you like the best.
The two he linked are both very high quality modular PSUs. If you can afford that, go for it.
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April 14, 2013 5:12:37 AM

slicedtoad said:
Anything bronze rated and above by Seasonic, Corsair, Antec, PC P&C, XFX, Thermaltake, EVGA, NZXT, OCZ, Zalman, Cooler Master or Enermax at 900W or higher is fine. Pick whichever is cheapest at wherever you shop or whichever you like the best.
The two he linked are both very high quality modular PSUs. If you can afford that, go for it.


okie .. got the point ... thanks guys for all your help and time .. i really appreciate and thankful to you all ... :) 

now I have one more question .. regarding the graphics cards .. do you think 3GB video memory that the 7970 has will be less to power my dell 27" 2560x1440 monitor?? as far as i know in sli/xfre vid mem do not scale up.. i mean even if i have 2x 7970 with 3GB mem each still in xfire they would not act as 6GB rather it will be 3gb only .. so do u think 3gb is sufficient?? or should i exchange them for the 6gb version of the same card sapphire has?
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April 14, 2013 8:38:26 AM

3GB is plenty. You will see games like BF3 taking up to 2.5GB of vram at that res. Most games won't go past 1.5GB though.

And you're right about memory not scaling.
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April 14, 2013 10:48:16 AM

slicedtoad said:
3GB is plenty. You will see games like BF3 taking up to 2.5GB of vram at that res. Most games won't go past 1.5GB though.

And you're right about memory not scaling.


Okay .. that sounds assuring ... but hey .. i just stumbled upon this feature on pcper ..Frame Rating Dissected: Full Details on Capture-based Graphics Performance Testing
basically what they are saying is that amd in xfire sucks big time because of runts (very small frame heights .. about 5 pixels which in effect hampers visuals and overall game-play) and dropped frames (this is clear from its name) .. this is somewhat cured if vsync is turned on but vsync also has its flaws and negatives .. whereas it seems from their tests that nvidia cards (690 and titan are applicable in my situation or even 2x 680s in sli) perform way better than comparable amd setup. so what say guys??? what do i do here??
This if true is horrible!! Do i need to reconsider my graphics cards also?? :ouch:  i mean do I need to get something like nvidia gtx690 or a titan may be .. as both of them cost as much as two 7970 vapor-x i am considering .. in india at least .. so please suggest guys .. this pcper report has raised a big red flag in my mind about my choice of hd7970s in xfire!!! :??:  pls help!!!
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April 15, 2013 12:10:17 AM

Alright, let's dig into the world of runt frames. If you don't feel like reading a wall of text, you can skip the spoiler.

Spoiler
They're new. Well, actually they've likely been around since SLI/CF was introduced but we only just started paying attention to them.

For the past two year or so (I could be off a bit), Nvidia has been trying to bring attention to them and a month or two ago, they released their FCAT datapath frame monitoring tool to reviewers. It's purpose is to count 'runt' frames so they can be discarded instead of counted as a fps. I'll try to explain what a runt is and why it is.

Simplified version of how a game engine works:
-A 3d coordinate space holds the locations of the game's polygons (everything visual in the game).
-This 3d space can be mapped to your screen based on the cameras position+lighting+textures+etc.
-Anytime something happens (camera moves, object moves, object changes, lighting changes, wtvr) the game engine needs to recalculate what is shown on your screen (plus a whole bunch of other things).

Now when I say "game engine", I should be saying "graphics pipeline". It's is made up of the actual engine (like Frostbyte 2, for example), DirectX (or some alternative), the GPU drivers, the GPU itself and finally the monitor. This pic from Tom's runt frame article shows the process:


In a simple system, DX would tell the GPU what to calculate and to display it. Frame variance would be completely dependent on the game's engine and DX. But when you add two cards, you have to alternate frames between them. This means you have to guess at how long a frame will take to load and try to balance the load somehow while keeping the two cards in sync. It's a really complicated process that's seen tremendous improvement over the last few years. But basically the GPUs spit out frames* whenever they can even if the frame is tiny.

*For optimization purposes (and other complications), a frame can be any subset of pixel rows.

Now, what Nvidia has done is implemented some sort of mechanism (at the driver level) that tries to control when frames are displayed to avoid tiny subsets of rows from being displayed (runts).


The problem with this being so new is that no one has truly explored it. What would happen if you made the definition of "runt" slightly larger? Smaller? What if you took average frame size into account? No one has even tweaked nvidia script for calculating these runt frames.

The article you linked uses % of screen size as it's runt definition. Tom's used a fixed size. Tom's has far better results (still slightly in nvidia's favor). And both of these scripts were provided by Nvidia.

If it turns out that these finding are as serious as Nvidia thinks, AMD will respond with a driver update. Who knows how long it will take but they've been pretty good with drivers recently.

You also have vsync. It seems to completely fix the runt problem. There is a cost in latency but it's not enough for me to notice.

So, once again, I'd say you're fine. Just turn on vsync and you should be good to go until further notice on the runt situation.

If you do decide that you need to make a swap, 2 670s would be the way to go. Make sure they're the 4GB versions. The difference btwn the 670 and 680 is tiny compared to the price gap, so 680s are not recommended.

Note though, that 7970s are more powerful than 670s (or 680s) and this problem (if it turns out to be as serious as Nvidia says) is a software rather than hardware problem.
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April 16, 2013 8:45:28 AM

slicedtoad said:
Alright, let's dig into the world of runt frames. If you don't feel like reading a wall of text, you can skip the spoiler.

Spoiler
They're new. Well, actually they've likely been around since SLI/CF was introduced but we only just started paying attention to them.

For the past two year or so (I could be off a bit), Nvidia has been trying to bring attention to them and a month or two ago, they released their FCAT datapath frame monitoring tool to reviewers. It's purpose is to count 'runt' frames so they can be discarded instead of counted as a fps. I'll try to explain what a runt is and why it is.

Simplified version of how a game engine works:
-A 3d coordinate space holds the locations of the game's polygons (everything visual in the game).
-This 3d space can be mapped to your screen based on the cameras position+lighting+textures+etc.
-Anytime something happens (camera moves, object moves, object changes, lighting changes, wtvr) the game engine needs to recalculate what is shown on your screen (plus a whole bunch of other things).

Now when I say "game engine", I should be saying "graphics pipeline". It's is made up of the actual engine (like Frostbyte 2, for example), DirectX (or some alternative), the GPU drivers, the GPU itself and finally the monitor. This pic from Tom's runt frame article shows the process:


In a simple system, DX would tell the GPU what to calculate and to display it. Frame variance would be completely dependent on the game's engine and DX. But when you add two cards, you have to alternate frames between them. This means you have to guess at how long a frame will take to load and try to balance the load somehow while keeping the two cards in sync. It's a really complicated process that's seen tremendous improvement over the last few years. But basically the GPUs spit out frames* whenever they can even if the frame is tiny.

*For optimization purposes (and other complications), a frame can be any subset of pixel rows.

Now, what Nvidia has done is implemented some sort of mechanism (at the driver level) that tries to control when frames are displayed to avoid tiny subsets of rows from being displayed (runts).


The problem with this being so new is that no one has truly explored it. What would happen if you made the definition of "runt" slightly larger? Smaller? What if you took average frame size into account? No one has even tweaked nvidia script for calculating these runt frames.

The article you linked uses % of screen size as it's runt definition. Tom's used a fixed size. Tom's has far better results (still slightly in nvidia's favor). And both of these scripts were provided by Nvidia.

If it turns out that these finding are as serious as Nvidia thinks, AMD will respond with a driver update. Who knows how long it will take but they've been pretty good with drivers recently.

You also have vsync. It seems to completely fix the runt problem. There is a cost in latency but it's not enough for me to notice.

So, once again, I'd say you're fine. Just turn on vsync and you should be good to go until further notice on the runt situation.

If you do decide that you need to make a swap, 2 670s would be the way to go. Make sure they're the 4GB versions. The difference btwn the 670 and 680 is tiny compared to the price gap, so 680s are not recommended.

Note though, that 7970s are more powerful than 670s (or 680s) and this problem (if it turns out to be as serious as Nvidia says) is a software rather than hardware problem.


I like reading them :)  .. I am going through the reports on tom's .. i am also leaning towards keeping my dual 7970s .. as I know that they are more powerful than nv cards .. hopefully I will keep them .. but before that I want to read up everything regarding this little nuisance :pfff: 
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April 30, 2013 2:05:36 AM

Hi guys,

I have finally decided on upgrading the PSU for peace fo mind :)  I returned my GS800 and got the Corsair HX1050 instead and stayed with 2x HD7970 GHz Ed cards... Thanks very much all of you for your time and suggestions.. I really appreicate them!!

Cheers!
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April 30, 2013 2:14:03 AM

FYI guys ... I swapped my Dell UltraSharp U2713HM with ASUS PB278Q :wahoo: 
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April 30, 2013 3:40:26 AM

No problem.Your welcome!
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April 30, 2013 10:27:28 AM

Damn, that's a nice system. It's like as high-end as you can get without getting into problematic 3way sli/cf or custom water loops. I worry that you might become too immersed in BF3 and come out with PTSD :D .
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April 30, 2013 11:29:25 AM

slicedtoad said:
Damn, that's a nice system. It's like as high-end as you can get without getting into problematic 3way sli/cf or custom water loops. I worry that you might become too immersed in BF3 and come out with PTSD :D .


Lol... PTSD .. am so immersed in CRYSIS 3 and FC 3 now that I don have enough time to get PTSD!!! :D 
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