There is some need to be aware of the amount of GPU memory used in volume rendering. The structured volume renderer uses 2 bytes per sample for nodal variables, and 4 bytes per sample for element centered variables. So, 2Gb or 4Gb for a 1000x1000x1000 volume. It also uses some memory based on screen size. It uses 72 bytes per pixel. On a 4K monitor, in full screen mode, 576Mb of additional GPU memory would be used.