Renders are sometimes fast sometimes slow

truemadscientist

Daz Studio sometimes renders fast and sometimes incredibly slow in the same scene. Once it's slow, I have to restart my computer for it to go faster again. Why is this happening?

Fast is about 100 iterations a minute and slow is about 100 iterations in 10-15 minutes

hansolocambo

I had that exact same issue with my precedent rig. i7-7800X, RTX 2070S 8GB of VRAM.

I could work fine, with Iray in the viewport for quiet some time. But I knew that after a while (I never pinpointed the "why") it would slow down to a crawl. Instead of rendering a sample every few seconds, it would render 1 sample in a few minutes. It was insanely slower. And, because VRAM cannot be refreshed, I also had to restart. And then things would be fine again.

Since I changed my rig totally. And moved to an i9-12900K, RTX 3090 24GB of VRAM, it's so impressively fast that if the same happens I just did not notice it yet. I can work all day long in Iray mode without feeling any slow down.

So... it's a know issue. And it happens with some cards (that's just my feeling about the problem for having faced it for years) that don't have much VRAM (≤8GB). I guess some operations in Iray do no stop properly and go in a loop that slowly saturates the card. There's no solution that I know of, except a restart.

What I used to do : work avoiding Iray in the viewport except when necessary. And restart (always) before rendering the final image. Because the rendering time of a rather complex scene could go from 3 hours (when everyting works fine) to such an insane amount of time that I would stop it after one night calculating for nothing.

Only sound advice I can give here : when your scene is all set up, restart Windows before rendering.

Good luck   ¯\_(ツ)_/¯