The iray FAQ

Posted by Shane Griffith, 29 September 2010 7:00 pm

The Autodesk® Subscription Advantage Pack for Autodesk® 3ds Max® 2011 & Autodesk® 3ds Max® Design 2011 software integrates the latest state-of-the-art technology from NVIDIA and Mental Images who are working with Autodesk to revolutionize rendering and simulation workflows. This exclusive Autodesk Subscription only release features one of the world’s first physically accurate “point-and-shoot” renderers, the iray® rendering technology from mental images. Creating realistic images has never been easier with 3ds Max, using iray eliminates the need to spend countless hours tweaking sample settings and other tedious render settings. Unfortunately for a few of you this means fewer coffee breaks, but at least there’s no more need to do the magic numbers dance each click of the render button. The workflow is now simplified to the point where you feel like you are rendering with a digital camera. You can now spend your valuable time focusing on shot composition and more creative aspects of creating the imagery rather than tweaking some settings, clicking render, go get coffee, chat with your cubicle neighbor, drink more coffee, “oh crap got it wrong”, tweak some more settings, click render, go get coffee, chat with your co-worker, drink coffee again, “oh crap..”, repeat until time to go home….

However, with this new dawn of GPU accelerated processing comes a whole new set of technical knowhow and hardware understanding. As some might have already experienced results can certainly vary machine config to machine config. This makes it difficult for us to provide more general best practices, but what I have gathered here is a list of common questions that have been raised so far today. If you have additional questions please feel free to drop a comment at the bottom as we plan to take all this information and create a more formal FAQ to be placed on the
3ds Max product center page.


iray FAQ

  • Does 3ds Max use both CPU & GPU hardware while rendering with iray?

Yes – iray uses all the CPUs and CUDA-capable GPUs it finds within your system simultaneously.

  • What graphics hardware is required to use iray’s GPU acceleration?

The iray renderer within the Subscription Advantage Pack for 3ds Max 2011 takes advantage of the NVIDIA CUDA architecture and gains considerable acceleration from any CUDA-capable NVIDIA GPU. This allows iray to gain acceleration from over 250million GPUs shipped over the past 4 years.

  • What are the performance differences for iray between NVIDIA’s GeForce, Quadro, and Tesla products in 3ds Max?

NVIDIA GPUs vary in their compute performance according to the number of CUDA cores they have, the GPU’s clock speed, and the GPU’s architecture. The GPU brand will not impact iray performance beyond these characteristics. Put into formulae, GPU ray tracing performance looks like this:

(CUDA Cores#) x (Clock Speed) x (GPU Architecture) = Relative Performance.

This means that for a given GPU architecture and clock speed, iray performance will scale linearly with the number of CUDA cores present on the GPU, and for a given architecture and core count iray will scale linearly with clock speed. The GPU family (Quadro, Tesla or GeForce) does not have additional influence on how iray uses it.

Note, an exhaustive list of GPU characteristics can be found here

  • What are the advantages of Quadro and Telsa boards over GeForce cards?

At a high level, GeForce products are designed for the ultimate gaming performance, Tesla is designed for the best compute performance and capabilities, and Quadro is a superset of both the best in graphics and compute. While each GPU family has different features, for GPU ray tracing the primary difference is in reliability and maximum scene size. NVIDIA oversees the manufacturing of its professional products (Quadro and Tesla), ensuring each product is available for three years and warranted for three years. Consumer products (GeForce) are manufactured by numerous companies and have much less availability and warranty. NVIDIA’s professional products may have slower clock rates than their comparable consumer products to fit within the power constraints and reliability needs of workstations and server rooms. Quadro and Tesla products also offer much more memory than GeForce products, allowing far larger 3ds Max scenes to be accelerated by the GPU. NVIDIA only warranties Tesla and Quadro products for running in a server room environment, where non-stop computing is typical – as with a dedicated render farm.

While it’s much more affordable to outfit your workstation with a GeForce card, in the long term you may have to replace that hardware more frequently and there might be risk of a major meltdown if you don't take extra precautions. With iray renderings you will be putting the hardware under unusually long strains that the card is not equipped to handle.

  •  Do I need an SLI certified motherboard to use multiple GPUs for iray rendering?

No – SLI is not needed to use multiple GPUs for iray. Iray will use whatever GPUs it sees within the system, regardless of whether the motherboard is SLI certified or the boards are placed in SLI mode.

  • What NVIDIA Driver settings should I make to ensure iray runs as well as possible?

For best iray performance, please ensure the following are set within the NVIDIA Control Panel:
- SLI should be OFF (for multi-GPU systems)
- ECC should be OFF (for Quadro and Tesla GPUs based on “Fermi”)
- PhysX should be set to CPU

  • Do NVIDIA GPUs support Direct3D and OpenGL in 3ds Max?

Both GeForce and Quadro boards support Direct3D and OpenGL, although the drivers may behave somewhat differently as GeForce drivers are tuned for Games performance while Quadro drivers are tuned for Tools performance. Direct3D is the most feature rich graphics API for 3ds Max, and Quadro products include a 3ds Max Performance Driver for additional performance when using Direct3D. In contrast, Tesla boards have minimal graphics API support and are not recommended for driving graphics applications. Tesla products based on the Fermi architecture have DVI ports, but this is solely to make it easy to load the NVIDIA driver (earlier Tesla products had no video out).

  • What NVIDIA GPU rendering options are available for data centers?

NVIDIA’s Tesla products are designed for server rooms, with the “M” (Module) series being add-in boards for 1u systems which provide their own active cooling. Solutions vendors can be found here. NVIDIA also provides some “S” (Server) solutions that are 1u systems that connect to a CPU unit via a PIC Express cable. The S2050 (Fermi class) is the latest product here, but it’s also likely the last, as NVIDIA has found third parties are better equipped to provide such solutions from Tesla M class products.

  • Can I setup data center GPUs for use with workstations.

No. Tesla M products are passively cooled and do not include fans, so they will not operate in a PC or workstation. Conversely, there’s no issue using Tesla C products (which are actively cooled with their own fans) in a dedicated server.

  • What is RealityServer and is it required for data center rendering?

RealityServer is a platform product for Web developers to create server-based applications that employ 3D Web services that enable Web clients to interact with 3D data remotely. RealityServer provides numerous rendering modes for processing server-side data, with its iray mode being compatible with the iray renderer within 3ds Max. This commonality allows a RealityServer application to accept 3ds Max scenes (prepared for iray) and deliver a result that is identical to what a 3ds Max session renders. While RealityServer provides a unique and powerful option for processing 3ds Max content remotely, it is in no way required for 3ds Max users to render with iray across their LAN using Autodesk Backburner.

  • I’m using just one NVIDIA graphics board – can it be used for iray as well as my viewport graphics?

Yes. The same GPU powering 3ds Max can also be used to accelerate iray. When this is done, you may find your Windows GUI interaction is sluggish while iray is rendering.

  • What options are available for NVIDIA multi-GPUs and 3ds Max?

Iray will automatically take advantage of all CUDA-capable GPUs within the system – as it does with CPUs. Iray will run well on all classes of NVIDIA GPUs – GeForce, Quadro, and Tesla.

  • How does the performance scale with NVIDIA multi-GPU cards (are two cards twice as fast as one)?

Performance for iray should scale nearly linearly between the same GPUs – as it is across CPUs.

  • Does NVIDIA GPU cards accelerate Distributed Bucket Rendering (DBR) or support parallel rendering in 3ds Max?

No. iray is not currently compatible with DBR within 3ds Max.

  • Will iray work with 3ds Max BackBurner network rendering?

Yes - GPUs on networked machines will be used in the same way that CPUs are when called upon to render individual frames.

  • How do I enable GPU rendering in 3ds Max?

Iray automatically leverages any CUDA-capable GPU it finds within the system, along with any CPU. There is no user interface for enabling this (or tuning it off) – it just happens.

  • What are the performance differences with 3ds Max CPU rendering verses iray GPU rendering?

This will vary between the GPUs and CPUs being compared, but between newly purchased, top-end processors, a Tesla GPU is rougly +6X faster than a single quad core CPU.

  • How can I tell how much performance I’m getting from either the CPU or GPU if iray is always using both?

3ds Max 2011 doesn’t provide a user interface for controlling how iray uses CPUs and/or GPUs. There are MaxScript commands that can be used to control which processers are used. Just enter these lines in the MaxScript Listener to control what processors iray uses:

mental_ray_string_options.addoption "iray devices" "0 1"

Controls what GPUs iray will use. The last string states which GPU is in use with “” meaning none, “0” being the display device, “1” being just the secondary GPU, “0 1” being both GPUs, and so on.

mental_ray_string_options.addoption "iray threads" 4

Controls how many CPU threads iray will use. The last string determines the number, with 0 not using the CPU at all and 4 being typical for a quad-core. To set iray to use all available CPU threads enter:

mental_ray_string_options.addoption "iray threads" sysinfo.cpucount

*Be careful note to set “iray devices” to “” and “iray threads” at the same time because there will be nothing for iray to use when you render.

For example:
Use only the CPU:
mental_ray_string_options.addoption "iray threads" sysinfo.cpucount
mental_ray_string_options.addoption "iray devices" ""

Use only the GPU (when you have 2):
mental_ray_string_options.addoption "iray threads" 0
mental_ray_string_options.addoption "iray devices" "0 1"

Use both CPU and GPU (when you have 2):
mental_ray_string_options.addoption "iray threads" sysinfo.cpucount
mental_ray_string_options.addoption "iray devices" "0 1"

or you can just try this tool

  • How much GPU memory is needed for 3ds Max iray rendering?

The entire scene must fit into GPU graphics memory in order for iray to take advantage of GPU acceleration. If the scene does not fit unto into a GPU’s memory, that GPU is ignored and all processing takes place on the CPU and in RAM and run much more slowly. If the scene exceeds RAM, then iray will use virtual memory and run more slowly yet. For estimating memory usage, budget about 1 GB per 8 million triangles, to which you must also add 3 bytes/pixel for any referenced bitmaps.

  • Do NVIDIA GPU cards also use system memory for iray rendering?

3ds Max uses system memory for processing the scene, and iray uses it for utilizing the CPU. When iray is rendering, the CPU and GPU will be consuming a similar amount of memory in graphics and system memory (respectively).

  • If I have three NVIDIA cards in my workstation that each have 1GB of video memory can I render scenes that use up to 3GB of memory?

The entire scene must fit entirely into GPU memory on each GPU in order to use that GPU for processing. In this example, the maximum scene size is 1GB, and scenes over 1GB would be rendering exclusively on the CPU.

  • What if I render a 2GB scene and have one GPU that has 1GB and another that has 3GB?

In this case, iray will ignore the 1GB GPU and only utilize the 3GB GPU (along with the CPUs)

  • Do NVIDIA GPU cards support ECC memory?

Yes, the latest Quadro and Tesla “Fermi” generation boards support ECC, but using it will not increase accuracy or performance for iray. It is recommended that ECC is always turned OFF when rendering with iray.

  • How can I view my NVIDIA GPU load and GPU memory usage?

There are third party utilities for this such as: and GPU-Z

  • What companies offer NVIDIA Tesla or Quadro configured workstations?

Most vendors have preconfigured options, including HP, Dell, Lenovo, PNY, BOXX, etc.
For Quadro solutions see:
For Tesla solutions see:

  • Can I build my own multi-Tesla computer?

Yes. Telsa “C” (card) products are similar to standard graphics boards and are easy to add to standard PC’s. Tesla “M” (module) products are designed for 1u heights in rack mounted systems that provide their own cooling. A motherboard layout for accommodating the number of full length boards you wish to include, and an adequate power supply for powering them, will be two of your primary design choices.

  • Can I mix Quadro, Telsa and GeForce boards? If so, what driver do I use?

Yes. For drivers, you should load the one driving your Windows display.

  • Can I mix GPUs of different generations and memory size?

Yes, iray supports the use of different generation GPUs.

  • What do you recommend for optimal iray performance?

For workstations, a Quadro graphics board and as many Tesla “C” boards as can fit in the box will give you the most reliable, high performance blend of interactive graphics and GPU ray tracing performance while also accommodating the largest possible scenes.

For dedicated render servers, the Tesla “C” or “M” products deliver the most reliable, high performance for GPU ray tracing. Quadro products can be used here too, but will not provide added benefit over Tesla unless they are also serving Direct3D or OpenGL graphics in applications other than iray rendering. GeForce products are not warranted for data center use.

For portable rendering, there will soon be laptops with mobile GPUs based on the Fermi architecture that will provide very reasonable performance (the equivalent of several quad-core CPUs). Because NVIDIA never made a GT200 mobile part, these new laptops will be many times faster than any laptop from earlier this summer.

  • When building a system for iray performance, is it best to add an additional CPU or GPU?

Given that a new GPU is worth numerous quad-core CPUs, it’s far more cost effective to add an additional GPU rather than a CPU for increasing iray rendering speed.

  • How much slower does iray run when my scene exceeds graphics memory?

When your processed scene size exceeds the memory on your GPU, iray automatically switches to only using the CPU, and will run at the speed your CPU(s) can process.

  • How much slower is a GPU placed in Gen1 x8 PCI Express slots versus in a Gen2 x16 PCI Express slot?

For operations that are constantly updated, like viewport interactive graphics, Gen1 is much slower than Gen 2. For compute-intensive operations that keep the GPU very busy before sending its results across the bus there is nearly no difference between the two PCIX types. In the case of iray and GPU ray tracing, you might see a GPU render faster on a Gen2 slot when the scene is very simple, but nearly no difference on a Gen1 slot when the scene is reasonably complex.

  • Can a render farm mix the use of GPUs and CPUs – some using only CPUs, some with GPUs?

Yes. Iray delivers the exact same result on GPUs and CPUs and so can be used in highly heterogeneous GPU & CPU environments.

  • Can a render farm mix GPU generations? e.g., some using Quadro FX 5800 (GT200 generation) and others using Quadro 6000’s (GF100 generation)

Yes. Iray delivers the exact same result across GPU generations, and can be used in farms having different GPU generations.

  • Does iray render depth of field and motion blur effects?

Yes - iray can render depth of field effects
No - iray does not render motion blur effects at this time

  • Can I render animation sequences with iray?

Yes. you can set iray to render the same number of iterations per frame that will create predictive results frame to frame. You can also specify time spent rendering per frame if you need to get results within a fixed time period. For example: if you have a 2 minute animation sequence to render overnight (12 hours), then you can set iray to render 12 seconds per frame. If you use BackBurner to distribute the frames across several machines you can then increase the time per frame to get better results.

Autodesk Subscription Advantage Pack for Autodesk 3ds Max & 3ds Max Design 2011 Help



Wow that was a lot more than even I thought I could hammer out!! Truth is I had a lot of help ;) but now that I've become the encyclopedia for GPUs and iray please ask away. If I don't know the answer then I’ll try to get one of the real experts to help us out.



Shane Griffith
Product Manager - 3ds Max & 3ds Max Design
Media and Entertainment Division
Autodesk, Inc





Posted 29 September 2010 5:39 am

Thanks Shane!!! Purely wonderful information!!! This is obvioulsy just the beginning of something great!

Ramy Hanna

Posted 29 September 2010 1:46 pm

Shane, congrats and well done to Autodesk and mental images on iray!


Posted 29 September 2010 1:59 pm

Thanks you, Shane.


Posted 29 September 2010 2:17 pm

"Can't render motion blur at this point"

Too bad, but i hope we'll see it eventually.


Posted 29 September 2010 3:34 pm

Thanks. I look forward to it. Though I will be back home by then so will wait 'till tomorrow, after the rush on your servers.

Shane Griffith

Posted 29 September 2010 4:14 pm

Hair, No (will add to the FAQ)
displacement, yes (need to confirm but am pretty sure)
I'll get more information on the materials here shortly, the help docs should be coming online and will help a lot with this.


Posted 29 September 2010 4:22 pm

There is some specific info on suppoerted materials and shaders on Ken's blog. I thought I read somewhere that displacement is supported, but don't know where.
Regarding hair, what if it's mr prim hair with a supported mr shader applied? I would have thought that would work, but I really don't know.

Shane Griffith

Posted 29 September 2010 4:41 pm

more info in the help docs, unfortunately i wont get a chance to update the FAQ until later tonight...


Posted 29 September 2010 5:50 pm

So Volume Light, Glow, Dust are not possible...That's a bit sad, as i do need them quite often.
Not working Object Properties is also a little sad, as i often use some shadows from hidden objects.


Posted 29 September 2010 5:53 pm

What about the Submerge Shader - i guess it's not needed anymore, because iray is just physically correctly rendering the submerge colors and the fade out at a specific depth?

Phil Miller

Posted 29 September 2010 6:18 pm

>>does that mean, that whether a scene fit's into the GPU's memory or not does not depend on rendering resolution and size,....?

The output image size impacts the time it takes to render and does not impact the memory used to render it.


Posted 29 September 2010 8:53 pm

Not really accurate Phil. Using the released Advantage Pack with a Quadro FX 4600 w/ 768MB of RAM:

resolution / memory used (logged with GPU-Z)
500x500 / 284 MB
1000x1000 / 301 MB
2000x2000 / 376 MB
3000x3000 / 500 MB
4000x4000 / 674 MB
4500x4500 / 652 MB (render artifacts due to hitting card memory limit)
5000x5000 / *154 MB (application crashed while trying to load scene into GPU memory)


Shane Griffith

Posted 29 September 2010 9:24 pm

thanks Eric, we will have to get more info from dev. It was my understanding the frame buffer was being allocated in system Ram


Posted 29 September 2010 9:44 pm

OK i still don't see it in my German subscription site. Is the localized version coming to us later?? I was really hoping it will be available today.

Phil Miller

Posted 29 September 2010 10:53 pm

>>Not really accurate Phil.

My mistake - and thanks for running the test. I was only thinking of the image buffer (which is small) and not the allocation which is behind the scenes. You're showing about 24 bytes/pixel and that makes sense.


Posted 30 September 2010 5:40 am

render artifacts? Die you disable the CPU for this test, or why are there artifacts when reaching the card memory limit?
By the way, what happens, if the GPU memory is filled with Data (for example because of the Viewport Data). Is iray only using the memory, which is FREE on the card, or can it use the full amount of MB for the scene?


Posted 30 September 2010 9:46 am

I've been getting white speckles too, with reflective/refractive materials. I was wondering if iray does caustics since it's meant to be physically accurate. I thought maybe the speckles are caustics that need a hall of a lot of passes to look any good.

Jonathan de Blok

Posted 30 September 2010 10:01 am

yeah, iray does caustics, see the same thread a few post earlier. But I dont think the specks are normal, i've let it run for over half an hour and they do fade a little but it doesn't seem to go away at all.

And I did see these in any of the previews as well.

Jonathan de Blok

Posted 30 September 2010 10:02 am

typo: *did not* see in these in the previes


Posted 30 September 2010 10:14 am

Please anyone from the Autodesk manaers/developes: comment on these bright pixels which make just no sense

Jonathan de Blok

Posted 30 September 2010 10:14 am

Can I edit my messages here?

Anyways I dont think it's caustics since the specks end up in dark areas as well, far away from the object. So the distance from the light to the speck is shorten then via the reflection of the teapot. So that cannot go from a near dark to a full bright do to a stray caustics ray.


Posted 30 September 2010 11:03 am

I'm going to stick my neck out and say it is caustics, or that's the way it looks from tests I've been doing.

Jonathan de Blok

Posted 30 September 2010 11:18 am

Yeah it seems to be caustic related (only happens with reflective/refractive object in the scene)

But I did some test and brigth pixels showup on places caustics connot be so brigth, so maybe its a bug in the caustics calculations.

That pixel the arrow is pointing to cannot be a legit value I think:


Posted 30 September 2010 11:26 am

I set up a scene to deliberately get caustic effects. I've seen very bright pixels too, scattered far from the object, but over time with more passes they do decrease and blen into insignificance. The bright areas you expect to see caustics in are still a bit grainy though, I guess they take time to smooth out.

Jonathan de Blok

Posted 30 September 2010 11:47 am

I still think its a bug, check this image out after a few minutes those specks weren't going anywhere, they get less bright indeed, but remain visible.

Look at those in the left/back.. no way those are proper caustics.

This happens in both 32 and 64bit, CPU and/or GPU.

Shane Griffith

Posted 30 September 2010 1:01 pm

You’ll mostly see white specs if the scene contains difficult caustics, but hopefully they go away after enough iterations.


Posted 30 September 2010 2:42 pm

what? iray doesn't support composite map? What about composite material, i use it all the time, is it supported??


Posted 30 September 2010 3:13 pm

i'm so sad i got the german version of all the Autodesk software - we pay much, much more money for these localized versions and finally we get all the packs about 1 month later than the english subscribers. It's really too sad and definitely not logical. The translation of some few Words could not be something a big company like Autodesk need one month for.


Posted 30 September 2010 3:19 pm

And there is something else - the subscription year of many german/french customers might end before such localized Packs are ready: which leads to less service for the money compared to customers who have the english items. This is really not good.


Posted 30 September 2010 3:31 pm

The only maps that are supported are:

Mix (a mix within a mix doesn't seem to work properly either)
Normal Bump
Output (limited use)
RGB Multiply

The new Substance maps are not compatible and there is no composite material either. Only Arch and Design and Autodesk Materials. Basically any material for architectural visualization. It should work great for just that. But for product design and is pretty much useless.


Posted 30 September 2010 4:41 pm


I'm trying iray with an english Version of 3ds max Design within a trial period of 30 Days. I mus say i loaded one of my scenes with a lot of composite Material and...It works. So i guess you were wrong on that one.

Shane Griffith

Posted 30 September 2010 4:53 pm

@c0cllc "I'm trying iray with an English Version of 3ds max Design within a trial period of 30 Days."

and so how did you get the subscription extension if you don't own the product?

others, the material and lighting limitations are described in detail in the help docs i now linked in.


Posted 30 September 2010 5:14 pm

I own the german Version and there is a Link from Autodesk here:

where i can enter my Subscription Data and download the english Version of the Pack. Don't tell me this is illiegal?

Shane Griffith

Posted 30 September 2010 5:26 pm

ahh I see, no worries. I just found it odd. since we sell the localized version as a separate product the entitlements in sub center don't let us enable the download for the English build. what you are doing is fine and we're working on a fix for the bigger entitlement issue.


Posted 30 September 2010 7:18 pm

re:"Can I edit my messages here?"
- Yes, click the View All Comments link you will get a white edit link at the top of your posts.

- These are Caustics/glossy samples that haven't been given enough time to bake out. Most physically accurate renders can get them, as others have said. Any cheats to prevent them other than giving enough time would make the renderer no longer physically accurate/unbiased.

re:"I still think its a bug, check this image out after a few minutes those specks weren't going anywhere, they get less bright indeed, but remain visible."
- Actually those are valid caustics, since you have a reflective floor and teapot. That mean that any ray that hits the objects will generate a caustic ray.



Posted 30 September 2010 8:14 pm

I'm wondering how you can control the DOF with iRay. There is no lens shader slot in the render rollout, and no f-stop value.


Posted 30 September 2010 8:18 pm

re:"I'm wondering how you can control the DOF with iRay. There is no lens shader slot in the render rollout, and no f-stop value."
-Enable Depth of Field (mental ray) on your camera and adjust the f-stop value.


Jonathan de Blok

Posted 30 September 2010 8:34 pm

"Actually those are valid caustics, since you have a reflective floor and teapot. That mean that any ray that hits the objects will generate a caustic ray"

I understand that, what I had a hard time figuring out is why pixels far away get to be bright in the first place. The distance traveled from the lightsouce, via a reflective objects, is way longer then the direct route. the direct route gives a dark value, the long way around, via a spherical surface the should diverge the ray even further, gets calculated as bright?

I'm sure there must be a reason for that to happen, I just want to understand it better.

Other then this little thing it's brilliant! I'd love to have some more dails and buttons to adjust, esp in the caustics area and how the sampler does its thing. Sometimes photorealism is not what I'm after and I want to tweak things a little.


Posted 30 September 2010 10:35 pm

@c0cllc The scene will still render, but the materials that are composite, or others that are not compatible, will render grey, or black. You also cannot assign the composite material, or composite map while iray is set as the renderer. So it is not compatible, and will not work properly unless you have some super hacked version that the rest of us do not.

Here's the error code straight from the Render Message window, which I recommend you keep open so you can debug which materials and lights are not compatible. (Rendering menu, Render Message Window)
IRAY 0.11 warn : unsupported shader max_CompositeMaterial, defaulting to grey diffuse


Posted 1 October 2010 12:58 am

What graphics drivers are you using? How do you know the GPU isn't being used? What errors are you getting in the mental ray message window?



Posted 1 October 2010 1:06 am

Hi Eric
Thank for trying to help me
My drivers are 258.96, and when I launch a render, I saw all cpu at 100% in the task manager, the PC slow down during the render, but nothing in message windows, I have this notification : Num CPUs:12 Cuda device : 1


Posted 1 October 2010 1:16 am

FYI, Shane your maxscript commands will fail when run. It appears that you are using left (U+201C) and right (U+201D) quotes rather than standard quote marks (U+0022). This causes maxscript to not interpret the items as quotation marks. Replace the quote marks with a standard " and you should be fine. From the maxscript listener:

mental_ray_string_options.addoption "iray devices" ""

mental_ray_string_options.addoption “iray devices” “”
-- Syntax error: at bad, expected
-- In line: mental_ray_string_options.addoption “i



Posted 1 October 2010 1:22 am

You may want to download a GPU monitoring application, Shane listed one in his Blog but I have been using GPU-Z:

If you aren't given an error in the message window then iray is using all CUDA GPU(s) and CPU(s) to generate the result. You can also use the maxscript command Shane posted (once he fixes it) to disable the CPU(s) and only use the GPU.



Posted 1 October 2010 1:35 am

re : Eric
Thank you,
it work, with the command I can activate or deactivate GPU rendering


Posted 1 October 2010 7:43 am

Just installed my new Gainward GTX 460 with 2048MB of memory, but iray gives these errors and refuses to use the GPU for rendering:

IRAY 0.7 error: CUDA device 0: unknown error
IRAY 0.7 error: CUDA error on device 0, cannot use this device for rendering
IRAY 0.7 error: image read failed on device 0
IRAY 0.7 error: CUDA device 0: unknown error
IRAY 0.7 error: CUDA error on device 0, cannot use this device for rendering
IRAY 0.7 error: z-buffer read failed on device 0
IRAY 0.7 error: rendering fragment failed on device 0

Bernard Lappe

Posted 1 October 2010 10:39 am

great information Shane! well done.


Posted 1 October 2010 1:01 pm

re:"Thanks for your explanation Eric, but I don't see an f-Stop value in any camera rollout."
You need to switch and enable the multi-pass Depth of Field (mental ray) effect in the camera (forgot the multi-pass part last post) . That is where you will get the f-stop control and be able to use it.


Shane Griffith

Posted 1 October 2010 1:22 pm

I've updated the Maxscript section, thanks loran, eric and phil for the help.

For those not being able to see the Advantage Pack in the subscription account, this is most likely occurring because you have purchased a non English version of the product and there is an issue on our side with these entitlements right now we are working on fixing this issue. Also the localized version of the Adv Pack should be released October 15th.

I'll work on the other updates later this weekend, thanks everyone for the feedback


Posted 1 October 2010 7:25 pm

Thanks again Eric, I'll check it out.


Posted 3 October 2010 10:29 am

I played around with iRay, very promising, but I couldn't get a daylight system with mrSun and mrSky to work. mr Photographic Exposure turned to 15, etc., but the render remained black. Any tips? A tutorial about setting up a daylight scene with iRay would be much appreciated, thanks in advance.


Posted 6 October 2010 10:41 am

Iray Manager updated


Posted 6 October 2010 10:41 am

Iray Manager updated


Posted 6 October 2010 3:15 pm

Thanks for sharing the MaxScript!


Posted 8 October 2010 3:45 pm

to Rik72 :

I made a test with a NVIDIA 460 1GO + CPU I7 980X 6 cores 3.3 Ghz - 12 GO RAM
à scene with 3 millions poly, 3000 objects an 84 lights - output 480*270 - clayrender

- CPU+GPU 480*270 - 100 passes - 4 light bounces :
rendering time : 48 sec - translation time 4 sec - total 52 sec

- GPU only 480*270 - 100 passes - 4 light bounces :
rendering time : 76 sec - translation time 4 sec - total 80 sec

- CPU only 480*270 - 100 passes - 4 light bounces :
rendering time : 67 sec - translation time 4 sec - total 71 sec


Posted 10 October 2010 8:44 am

Does anyone else have trouble with buggy bright spots when lighting an iRay scene with only a HDRI environment map? The more shiny surfaces I've got in my scene, the more overbright pixels.

The problem looks familiar to a V-Ray problem when using reflective GI caustics and bright, shiny materials.


Posted 10 October 2010 9:02 am

I have to add to my previous post that it mainly occurs when the default lights are not deactivated yet (by adding a photometric light and turning it off).

I guess it's a matter of too much light energy bouncing around in a scene, combined with caustics.

Shane Griffith

Posted 10 October 2010 5:39 pm

You really want at least 1gb of graphics mem, 2gb would be recommended for high detailed scenes.


Posted 10 October 2010 6:01 pm

I was thinking more of telling Iray not to use the quadro card if scenes got too big. I've never used a quadro card before and I just wonder if I've missed out when it comes to viewport image quality and speed.

In addition to a possible quadro I think 2 x 2gig 460s is probably the best option.

Jonathan de Blok

Posted 10 October 2010 6:02 pm

See if you can pickup a 480 or a 460 with 2GB, if it runs CUDA it will work, make sure the cooling solution used on the card is enough, iray will push the hardware so keep an eye on the temperatures.

(btw the top Quadro has less cores and is clocked slower the a standard 480 so unless you need more the 2GB of mem a 480 will beat a Quadro-6000 on iray rendering )


Posted 10 October 2010 6:32 pm

Sounds fantastic but do the 4xx series cards work well with the max viewports. Do they work as well as a quadro would I mean. Autodesk and nvidea seem to imply that the 4xx series are realy tuned for gaming rather that accurate and fast material representation in a modeling package viewport. After all, when you think about it, our business is more than just waiting for a render, it's also dependant on the viewport quality/performance.

BTW, does iray work faster with an outside, directly lit scene as opposed to an indirect interior?

Jonathan de Blok

Posted 10 October 2010 7:09 pm

3dsMax's viewport is based on DirectX, which is the same tech used for most games. DirectX is DirectX.. it looks the same on a Quadro as on a Geforce.

The whole quadro accuracy thing is about 32bits/channel for the colors, you'll need a special monitor for that and even then it will need a trained eye to spot the difference. Those features are great when you're a doctor working on X-rays images and you need a zillion grayscale levels to spot tiny differences, 3dsmax viewport will work just fine without that.


Posted 10 October 2010 7:34 pm

I've read, that with the current CUDA version 3.1.1 only 2/3 of the CUDA cores of my GTX 460 are actively used. Is that true? I've also read, that CUDA 3.2 will give all CUDA cores activity. I've tried the developer driver from the NVIDIA developer website (260.61), which uses CUDA 3.2, but iray seems to be not working with that driver - the rendering process just hangs and the rendering windows stays black.


Posted 10 October 2010 10:08 pm

to c0cllc :
I've tried the latest beta drivers, 260.61, and effectively, it's much faster, with the old drivers, my CPU ( I7 980 ) was faster than the GTX 460, but with this last one, the 460 is faster.

CPU only : render time : 1 min 54 sec + 4 sec setup = 118 sec
GPU only : GTX 460 render time : 1 min 02 sec + 3 sec setup = 65 sec
CPU + GTX 460 : render time : 47 sec + 4 sec setup = 51 sec


Posted 11 October 2010 7:36 am

@Dom2207 :

are these results with the same setting as in your previous post? In your previous post your CPU+GPU was 52sec, with new drivers 51sec. So not much of a difference. The GPU became faster, but the CPU became MUCH slower (nearly doubled the time with the new drivers)???


Posted 11 October 2010 12:26 pm

to c0cllc :

It was the same scene, but I've changed some settings, the position of the camera is different and the most important, there were 500 passes not only 100.I'm sorry, but I've not saved the first test scene with the whole settings.
I've also noticed the max viewport is a bit reactive with this latest drivers.
I will make antother test this evening with old and news drivers and the same setting, so when can mesure the gain.


Posted 11 October 2010 12:58 pm


thanks! I've installed now the new 260.89 drivers which bring CUDA 3.2.1 and did some tests: i notice absolutely no difference compared to the 258.96! That's odd!


Posted 15 October 2010 9:14 pm

iray Manager v1.3 is out! check it out at :

Shane Griffith

Posted 15 October 2010 10:20 pm

@max ehrlich the +6x faster statement I believe is based on the 2050 model.

Unfortunately, I don't know how long the mr example took to render but that's really not the point. You can certainly get mr to render things extremely fast, but will the look be accurate or of the same quality? How much time would you spend tweaking sample settings and various other parameters? and how long did it take to learn those things? One of the goals for iray was to put the easy button on rendering great photo realistic images, the performance benefits you get from using high end graphics HW is really just a bonus (a good one). Over time the HW is only going to improve and thus making the benefits even greater.

Shane Griffith

Posted 16 October 2010 12:05 am

for a few dollars you could get a decent GTX 4xx card to give it a test. I wouldn't recommend building a production machine on this but it will give you a decent look at the workflow and capabilities.


Posted 18 October 2010 6:40 pm

iray Manager 1.4 is out!

Shane Griffith

Posted 23 October 2010 1:52 pm

Hi Rik, There's an error in my FAQ about iray being resolution independent. This incorrect as iray will allocate graphics memory for a certain portion of the pixel buffer, the larger the image output the more memory that will be used. Your problem is likely being compounded due to low system ram also. Mental Ray might not be showing this problem as it has an additional feature to tile the frame buffer in ram making it easier to render really large images on 32bit systems.

Jonathan de Blok

Posted 25 October 2010 4:15 pm

Now lets try making that pixel buffer 16 or 32 bits per channel (so thats 4x16 bit for a singel rgba per pixel), add a depth buffer and other G buffer channel to that.. and the stuff you see on screen need memory.. did I mention textures go into gpu mem as well? This goes fast and a twice as large area needs 4x the memory..

Shane Griffith

Posted 25 October 2010 4:33 pm

thanks Jonathan.

Rik, here are some clearer estimates.

Using a Quadro FX 4800 with 1500MB of dedicated video memory:

1000 x 1000 = 425 mb
2000 x 2000 = 555 mb
3000 x 3000 = 750 mb
5000 x 5000 = 1125 mb
6000 x 6000 = 1200 mb artifacts start to appear as memory limits are reached
7000 x 7000 = render fails

Shane Griffith

Posted 25 October 2010 7:12 pm

do you have a mr sun & sky in your empty scene? iray will bake a hdr image of the mr sun&sky to use and might be output resolution dependent also.


Posted 26 October 2010 8:04 am

Since we can mix different brand of GPU with iray. Does it mean that I could have a basic Quadro (say Quadro 600) to do the modeling with Quadro driver, and two GTX 470 to do the rendering in the same workstation? That would be awesome! BTW, does iray do texture baking aka Render to Texture?

Shane Griffith

Posted 27 October 2010 3:15 pm

Hi Rik, XP32 will be another limitation for you as the total addressable system memory is 2GB and often less. It doesn't matter that the system has 3GB installed in it as the OS will not allow you to use that much. There is a /3GB switch you can add to the boot.ini that will help a little, but ultimately you need a 64bit OS.


Posted 29 October 2010 6:06 pm

Hi Shane,
I've some problems with lights and highlights, when I use photometrics lights, there are no highlight on specular surfaces (maybe also on glossy surfaces), the only way I've found to have highlights is making light shape visible in rendering.
Do you know another way to do that, because when you activate the light shape visible in render, it's change the diffusion of light, it's seem to be less powerfull, the render is more grainy.

Shane Griffith

Posted 5 November 2010 3:18 pm

Hi Dom
This is "normal"

Path tracing renderers do not allow traditional CG hacks. Specular highlights are really a compositing technique that adds fake illumination based on the viewing angle, which are quick and not physically correct. This also requires that the renderer understand diffuse and specular separation.

Since iray doesn't treat diffuse and specular separately like traditional renderers, this distinction cannot be made. The only way (the physically correct way) to see highlights from lights on surfaces is to make them also visible to the eye, as shapes.


Posted 5 November 2010 7:18 pm

thanks for your help, Shane, but as I've told you, when you make the light shape visible, it's less powerfull than without, the image is more grainy and need more iteration to achieve something "smooth" to the eye.
I believe, but I'm not sure yet, that result is better with glow material on a meshe, does it mean I must change the way to light a scene, using glowing material instead of traditional light ?
In fact, in reality, a light source is always visible ( a bulb lamp, projector, etc..), so with IRAY, I must model my lights ?

ps : excuse my poor english, I'm french.


Posted 4 January 2011 12:27 pm

Many shaders (materials and textures) don't work as yet with iray. Best to stick to A&D or Autodesk/ProMats.
One way to get laquered car-type paint with A&D is this:-
Not tried it with iray though.


Posted 4 January 2011 12:38 pm

Hold on a min, Blend doesn't even work with iray, it's worse than I thought. Strange how it hides incompatible mats like blend, but you still see Ad Matallic Paint. It seems it does render, but there is no diffuse?


Posted 4 January 2011 2:14 pm

Thanks samab. I suppose this is becasue it's still a young product. Hopefully they will let us know soon about future plans for compatible materials.

It is confusing/dissapointing to see the materials available in slate but not actually working...


Posted 4 January 2011 2:23 pm

I think some of the limitations, like some procedural maps and the new substance maps are because it's new. They maybe didn't have time to re-write the shaders for iray, so maybe they will be in future versions.
But some shaders I think will never work with iray because they use non-physical hacks that don't fit into iray's physically correct rendering method.


Posted 20 May 2011 1:16 pm

Thanks for the comprehensive look on iray.

This gives a good idea of what to look out for in future farm setups when using iray.

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