I am currently trying to render a scene that I will turn into a poster. The final render is spread across three separate layers. I am rendering at a resolution of 6000 x 9000 with 1080 samples. My computer has an i7 7800k with 32g of ram and 2 GTX 970s (4g each). Each layer is taking around 5 to 8 hours to render, but by time it gets to the 2nd or possibly 3rd scene my computer just takes a dump and freezes. Is it possible to render a single layer save it, restart the computer, and render the second and so on? Thanks in advance!
You can control which layer(s) render(s) with the checkboxes next to the layer's names in the Properties panel > Render Layers tab. Only the layers that are checked will render. You can therefore check one layer, render it, save it, restart your computer, do the next two, and combine them all with the compositing that you probably have.