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Triple SLI Scaling GuidePost Date: 2007-12-14
Digital Storm Customer Service
Joined: 13 May 2008
Online Status: Offline
Topic: Triple SLI Scaling Guide
Posted: 14 Dec 2007 at 12:02pm
Tri SLI FAQ And Scaling Guide
Introduction: This guide is aimed at preparing those who are interested in using Nvidia's new TRI SLI technology. There are some software caveats and technological caveat that users must be aware of before attempting to build an SLI system. I will be updating this guide regularly as more hardware support becomes available.
Currently Supported Hardware
Chipset Support: 680I Chipset.
GPU Support: Geforce 8800 Ultra, Geforce 8800GTX.
Tri SLI Bridge Chip: The Tri SLI bridge is unique from other bridge chips as it transfers data from the bottom GPU to the top. The 3rd GPU to the second. And the Second GPU to the First. It has to do so in a unique configuration. You will not be able to use normal bridges in a conventional means to enable Tri SLI. And currently Tri SLI requires that the bridge chip be installed for SLI to enable.
Power and Cooling and Chasis
Power Supplies: Power is going to be one of the single most inportant decisions you will make when designing Tri SLI system. Nvidia recommends a system with no less than 1.1 Kilowatts of sustained power. This power guide operates under the circumstance you'll be running 3 8800 Ultra cards, 1 Quad Core Intel CPU, 2 Sata Drivers, and a DVD RW or Blue/HD DVD drive.
It's very important to keep in mind that you may be able to give or take slightly from these recommended specifications based on your components inside your case. However their recommendations is very spot on to where you should be aiming for power concerns. My test system listed below in the benchmark section has ran on a PC Power and Cooling 1 kilowatt PSU. And a PC Power and Cooling 1.2 Kilowatt system. However even on my system the loads came dangerously close to the 1 kilowatt range.
Nvidia has a list of recommended PSU's for Tri SLI listed on the website below under the section "Three Geforce 8800 Ultra".
Chasis And Cooling; This is a very important topic to discuss. Not every current chasis is going to be optimal for Tri SLI. There are several concerns users must be aware of when building. Nvidia does have a list of currently supported Chasis but this initial Chasis support will be limited as more Chasis become approved.
Cooling: The most important aspect of this chasis decision is actually the cooling. Three Geforce 8800 GTX/Ultra cards are packed very close together and generate a significant amount of heat. If your airflow is bad your system will overheat and Nvidia heat sentinel will become active and downclock your hardware to protect it. I have several suggestions which might help those wanting to build a Tri SLI case.
1: Ensure your system has both an intake and exhuast fan starting and ending on seperate ends of the system with air blowing in from the bottom and hot air exhuasting from the back
2: Have a case with side panel fans. The more air flow you get from them the better as they will ensure cooler operation from your 3 GPUs. Below is an example of what I would call a fairly "ideal" cooling solution for a closed case enviroment.
3: If you absolutely cannot create a case or use similar cooling to the one above. There is the last option. Open your case to free up airflow. While this may be less ideal to those who like neat systems. It will definately allow for more free air to enter the case. If you want to take a further extreme you can add a desk fan of some type blowing air in. This is currently what I am doing as my chasis is not even close to the required specs and I need to replace it first.
Note: The most important thing to note here is that cooling is important and should NOT be ignored. Doing so will likely result in system slow down due to higher tempatures. While your hardware will not be damaged. Nvidia's own software will throttle it to help protect it. To give you an idea of some of the tempatures my system has been operating at. Here's a display. I dont need to remind you that these tempatures can vary dependent on room tempature, Fans, ect.
User Interface and Configuring Profiles
Nway: Nway is Nvidia's step in making AFR compatible across all platforms. Ranging from 2 way SLI to Quad SLI. The beauty behind Nway is it will allow SLI to scale seemingly as you add additional GPUS. Since Nway makes use of AFR you should not see various issues that occurred in Quad SLI. Another thing to note is that Quad SLI users will benefit from this. Windows Vista does not suffer the frame rendering limitation that XP does. So Quad/3 Way users should see much better scaling on their systems than prior multi GPU platforms which exceeded 2 GPUS.
Enabling Tri SLI: Enabling Tri SLI is as simple as it is enabling SLI. You'll need the supported components but you shouldnt see any difference between enabling Tri SLI than a dual SLI system. Currently the system does not support the switching Single, Dual, Triple, Quad SLI. Your stuck using one or the other. And in order to enable dual SLI. You are currently forced to remove the 3rd GPU from your system.
Profiles and Management: Currently the profile management system is similar to what you'd see on typical SLI setup. You'll have the rendering modes of SFR, AFR, and AFR2. In addition you'll have 3 way AFR and 3 way AFR2. And for those running quad systems you'll also have the options of 4 way AFR, 4 way AFR2, and AFR to SFR.
Unfortunately the current system is leaves something to be desired. As if you change a default rendering profile from its default SLI rendering mode ((Which will typically be 3 way AFR on a TRI SLI system)) you will lose that profile. This makes switching between SLI and TRI SLI very difficult and tedious. Due the way Nway is currently setup. You cant switch between 2 way and 3 way AFR easily. The only way to do that is to take the 3rd GPU out and run SLI normally. However for software that does not currently support SLI. You can still enable and edit profiles just as you would before. For both 2 way and 3 way SLI.
Note: Nvidia has assured me that this bug will be corrected soon. The intention is for Nway is to allow for switching between 2 GPUS and 3 GPUs without having to adjust the profiles. This functionality should exist in future drivers. For now you are stuck with the existing system unfortunately.
Get Your Vista updated!
Updates: You really need to get your vista updated. There are a few very important hot fixes out there for SLI. And a new one specifically for Three Way SLI. Not installing these updates could cause you numerous problems. Get them installed before running any 3D application.
Three Way SLI Hotfix
DX10 Multi GPU Hot Fix
Virtual Addressing Hotfixes
Other important hotfixes here
A Small Look at Performance
Quick Note: Despite all the updates I have made to my system I still dont have the monitor I'd like to really show off three way SLI. So unfortunately there are some limitations to the titles which I can show. Something very important to consider. Tri SLI can become CPU limited fast.
Bioshock DirectX 9.0 Scaling
Thoughts: Bioshock in DirectX9 mode with AA enabled doesnt seem to have that problem. You get tremendous scaling in this application.
Thoughts: What blew my mind was Oblivion was actually CPU limited with 16x CSAA enabled with transparency Supersampling in a completely alpha covered enviroment. The scaling is minimal at best until you enable 16xQ. 16xQ shows significant scaling with transparency supersampling enabled.
Thoughts: Nvidia's current SLI rendering profile is optimised for an upcoming Crysis patch. I was wary whether or not to include them based upon what I already know. But since this is the current shipping product I decided to go ahead and release the data. Currently Crysis in DirectX 9.0 mode you gain the most benefit using 4xAA. You actually get pretty good scaling under those circumstances. Unfortunately without AA performance scaling is less than ideal. Specially under 3 way.
Crysis Note: There is an upcoming patch for Crysis which improves performance substancially. Especially with AA modes off. I have included the prepatch results for education purposes but once the patch becomes available I will be posting the DX10/DX 9.0 performance scaling with the patch as well. Last I heard the patch due date was imminent. I actually expected it to be out by now.
World of Warcraft
Thoughts: World of Warcraft is not a demanding game. However some places such as the map I benched are loaded with alpha textures. You turn on transparency supersampling and you end up with a pretty hefty GPU bottleneck. With 16xQ you still hit a CPU bottleneck with 3 way AFR. The scaling from 2 way is minimal. To see if this was a fault with 3 way or just a CPU bottleneck I decided to turn on an extremely demanding antialiasing mode known as 32xS. 32xS will bring just about anything to its knees due to the extreme fillrate requirements. And once you put the stress back on the GPU you will see pretty good scaling.
Thoughts and Conclusion
Thoughts: Three Way SLI isnt for everyone. There are alot of things you'll have to do to ensure your system is 3 way ready. Hopefully this guide will better prepare for what to expect. People are going to need to take every precaution to ensure their system is prepared. It's a bit less forgiving than SLI when it comes to power and heat. If your going to buy 3 way SLI. Make sure that you need it first. If your already CPU limited or running a small monitor it's not going to do you any good. If you have taken all this into consideration then please read below. 3 Way SLI might be for you.
Conclusion: Even Nvidia will be up front and candor and say that 3 Way SLI is not for everyone. As SLI in itself is a niche market, three way SLI is even more of a niche market. However currently 3 8800GTX/Ultra cards are the only way to achieve playable framerates at extremely high resolutions where a single or dual GPU just isnt cutting it. And with Crysis out there you need every bit of GPU help you can get. To be honest my biggest disappointment with 3 Way SLI is the limited GPU support. While I will be the first to acknowledge that not all multi GPU systems make sense. Why buy 3 8500GS cards when an 8800GTX will outperform them at all times? However there are exceptions to these facts such as the 8800GT. Which would have been a clear winner in the 3way SLI department. Unfortunately this just isnt currently possible. 3 Way SLI is aimed currently at the absolute high end. And that is the 8800GTX and 8800 Ultra. Nvidia assured me that 3 way support will continue to exist at a high end system builder level but obviously would not comment about unannounced products. That being said. I am really enjoying my system. As an SLI enthusiast this system has been alot of fun for me to work with and I have enjoyed it immensely. I think as the technology progresses and the profile system is completely revamped and more supporting products come out the platform will become even more appealing to the enthusiast.
Edited by skyR - 15 Jan 2008 at 1:27pm
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