Redshift for Houdini: Out-of-Core, VRAM Limits and When It Beats Karma

You have cached a heavy Pyro or VDB scene in Houdini, but Redshift still runs out of GPU memory even with out-of-core enabled. Out-of-core can reduce VRAM pressure for supported data, but it does not remove every GPU memory limit. This becomes especially important with Houdini volumes, which can consume significant GPU memory. In this guide, we look at redshift houdini vram out of core, its limits, and when Redshift may be a better fit than Karma for a Houdini workflow.

Out-of-core does not eliminate Redshift’s need for VRAM. Some data can be handled outside GPU memory, but other render data still requires VRAM. Most importantly for Houdini simulation work, Redshift requires volume objects to fit entirely in GPU memory. If the required volume data exceeds available VRAM, rendering can stop with an out-of-VRAM error even when out-of-core is enabled.

System memory also matters when Redshift relies on out-of-core data, so having more RAM can help with supported workloads. However, adding system RAM does not solve a volume that itself cannot fit within the GPU memory available to Redshift.

Redshift’s out-of-core system is designed to let supported data, including textures and geometry, exceed available VRAM by using system memory when necessary. But not every part of a render can be handled this way.

Volumes are a key exception. Redshift states that volume objects must be stored entirely in GPU memory and are not handled by its out-of-core system. This means out-of-core should be viewed as a way to extend memory capacity for supported data, rather than as unlimited VRAM.

Out-of-core processing can also introduce a performance cost compared with keeping the required data in GPU memory, so enough VRAM remains valuable even for scenes that can render successfully with out-of-core.

Houdini workflows frequently involve volume data from simulations. In USD workflows, SideFX documents volumes as collections of fields, including OpenVDB field assets for VDB data.

This matters with Redshift because its volume objects must fit entirely in GPU memory. Maxon specifically warns that having too many volume objects or volumes at particularly high resolutions can cause an out-of-VRAM error.

For heavy Pyro or other volume-based shots, reducing unnecessary volume data or resolution can therefore reduce GPU memory requirements. If the volume still exceeds available VRAM, a GPU with more memory may be necessary. Out-of-core alone cannot solve that particular limit.

Redshift can make more sense when your production pipeline is already built around Redshift and you want to keep the same renderer and established look-development workflow for the Houdini shot.

However, Redshift should not be chosen simply because it is GPU accelerated. Karma XPU also uses GPU acceleration together with CPU resources, while Karma itself is deeply integrated with Houdini’s USD and Solaris environment.

That gives Karma a natural workflow advantage for projects already centered on Solaris, USD and MaterialX. SideFX documents Karma XPU support for MaterialX and USD Preview shaders, although XPU also has feature limitations compared with Karma CPU.

For texture-heavy scenes, Redshift’s out-of-core capabilities can still be useful. But whether Redshift actually renders a particular Houdini shot faster than Karma should be determined by testing the same scene on the same hardware with comparable settings, rather than assuming one renderer is universally faster.

Karma can be the better choice when your Houdini pipeline is already centered on USD and Solaris. Karma is SideFX’s renderer designed for USD-based workflows in Solaris, making it a natural fit for projects already using this pipeline.

Licensing can also be a reason to stay with Karma. SideFX includes Karma rendering with Houdini licenses, while Redshift requires its own Maxon license.

For scenes that cannot fit within available GPU memory, Karma CPU provides a CPU-rendering alternative that does not depend on GPU VRAM. It still requires sufficient system memory for the scene, so this is an alternative memory path rather than a guarantee that every oversized scene will render.

For Redshift, more available VRAM gives the renderer more room for GPU-resident data, while sufficient system RAM supports CPU-side data and texture caching. This matters especially in Houdini volume workflows because Redshift requires volume objects to fit entirely in GPU memory, so out-of-core cannot compensate for a VDB that exceeds the available VRAM.

If your workstation is the limit, moving the same Houdini and Redshift project to a machine with a higher-VRAM GPU and more system RAM can provide the memory headroom the scene needs. That is where iRender becomes useful, giving you access to more powerful remote GPU hardware without rebuilding your existing workflow.

iRender offers a remote RTX 4090 with 24GB VRAM and 256GB RAM, giving Redshift more system memory for workloads that can benefit from out-of-core. However, the 24GB VRAM limit still matters for data that must remain on the GPU, including Redshift volumes. Adding more RTX 4090 GPUs does not turn their separate 24GB memory pools into one larger VRAM pool.

You have full control of the remote machine, so you can install the Houdini and Redshift versions required by your project. Redshift licensing remains your responsibility, and billing starts when the machine is running, so prepare your files before startup and use auto-shutdown when the render finishes.

Available configurations include:

• CPU: AMD Ryzen™ Threadripper™ PRO 3955WX (3.9-4.2GHz) and AMD Ryzen™ Threadripper™ PRO 5975WX (3.6-4.5GHz)
• GPU: 1/2/4/6/8 RTX 4090/5090

For new users, iRender currently offers a 100% bonus on the first deposit within 24 hrs of registration, giving you additional rendering credits to get started with larger projects.

Maximum Speed – Absolute Freedom

                                                    Source: help.maxon.net, sidefx.com/docs/houdini/ 

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1. Why does Redshift run out of memory in Houdini even with out-of-core enabled?
Redshift out-of-core can handle supported data such as textures and geometry, but it does not eliminate the need for VRAM. In particular, Redshift volume objects must fit entirely in GPU memory, so heavy Houdini volumes can still cause an out-of-VRAM error.

2. How much RAM does Redshift need for Houdini volumes?
There is no single RAM requirement for every Houdini scene. Memory usage depends on the scene and volume data. More system RAM can support Redshift’s out-of-core workloads, but it cannot replace the GPU memory required for volume objects.

3. Should I use Redshift or Karma for Houdini?
Redshift can make sense if your pipeline already uses Redshift and you want to keep its existing materials and rendering workflow. Karma is a natural choice for USD and Solaris-based workflows, while Karma CPU also provides an alternative when GPU VRAM is the constraint. Neither renderer is universally faster, so performance should be compared using the same scene and hardware.