Random blank frames in animation?

Hi there folks.

Yes, I’ve looked, there are loads of posts about blank frames, but not quite this problem.

I have an animation, Internal Engine, 3000 frames, exporting to png. I send the blend file to my cluster where a header node starts blender on 128 small board pcs. This actually works pretty well, I can get 3000 frames rendered in well under an hour.

But, some frames fail and I get a smaller than expected file size (the reason for png) I know these are duff, but there are also a load that appear to be perfectly acceptable graphic files, but are completely blank. I’m also getting random glitches in the graphics, where the file is mostly ok but will have a couple of horrible horizontal bands blotched onto the image. It’s not a geometry/settings/node problem as it’s completely random and if I manually set off a render of a problem frame it renders perfectly. I occasionally get nodes crash out, I haven’t traced the error messages yet, but this isn’t the cause of the blank frames.

So, what causes this?

The render settings are simple, no Overwrite and use Place holders. The place holders is a pretty crude blocking mechanism, but as all my nodes are connected to the same network drive on a managed samba share it shouldn’t cause any problems, and my tests so far show 128 files created immediately after sending out the cluster command, so there aren’t multiple pcs trying to write to the same files.

I’m using one material for the whole model and the results are the same if I render with a surface, wire, halo, volume, each render has resulted in many random failed frames, not the same frames.

I feel it important to say, during the last render which I think was a Halo material (want edges instead of verts, but that’s another thread!) no pc crashed, all 128 worked until the 3000 frames were completed.

Any ideas?

I should also add, I’m nowhere near any memory constraints, at peak I’m using 246M on 4Gb boards.

I can confirm after running another 3000 frames overnight, there are NO missing or corrupted frames using Cycles. I’m quite happy to use cycles, this would after all be the preferred end result, but thought I could save time testing with the internal engine.

As it’s only testing it’s certainly not a show stopper, it’s just annoying to have to sift through all the frames to find the duff ones.

But for now, low sample cycles seems to be the way to go. Just need 2.79b to him the ARM distro. (Hint, hint!!)