Managing expectations

My rig includes a GTX1070 8Gb gfx card, and as much as possible I render on GPU only.

Against the odds these days, I have a 2nd GTX1070 8Gb gfx card on the way (and I know, they are like hen’s teeth).

I bought this almost exclusively for Blender, but will probably also use the 2nd GPU as a passthrough for VirtualBox. The latter is irrelevant.

In Blender, can I expect a halving of rendering time by rendering on two GPUs?

EDIT - I know that the preparation (building bvh etc.) will not be improved. It is once the render actually starts that I’m interested in.

TIA

My understanding is that in those cases where you have two identical GPUs, you can expect to cut render times in half compared to using just one of them.

Thank you - I guess I’ll find out tomorrow when it arrives, assuming I don’t get a box of bricks instead.

I’ve benched a couple of scenes to test against.

I have two gtx 1070 ti’s (bought used, I’m not rich). Both 58 sec. One 113sec. So 1.95X speed on that test. Close enough to call it 2X.

OK - having got number 2, got fed up with crashing before I remember the BIOS reset and just re-enabling pushed my RAM back to 3Ghz (which it doesn’t like - 2933 is the sweet spot) I can confirm that actual render times, is double. The extra 5 - 10% Splododyne noticed is likely the pre-render prep.

I’m quite happy - probably better than a single 3900 series.