This page provides a tutorial on rendering large images with V-Ray.
Rendering very large images can be memory intensive as very large resolutions require more memory be added to the scene's own memory needs. This tutorial explains how to set up V-Ray to render very large images directly to disk, optimizing memory efficiency. By writing the rendering image file directly to disk, the memory buffer is disabled, saving on overall memory use. This is very advantageous for machines with limited memory.
The Progressive sampler type is not supported for rendering out large images in this way.
Optionally, turn on the Generate preview option so that V-Ray can generate a small resolution preview of the final result.
If you rendered to a .vrimg file, you can use the VRImg to OpenEXR tool to convert the file to a scanline-based OpenEXR file.
Due to increasing the resolution of the rendered image, you may find that the render settings may need to be revised to keep the render noise free due to the large size.