File size above 8.5GB indicates that BD-R is required. File size above ~23868MB indicates that BD-R DL is required. For my particular example I do not need to know where exactly the layer-break is (how much sectors are in each layer), it's somewhere in half of the disc. I need to write half of the file from beginning of the disc and second half of the file to the end of the disc. For the reason I mentioned before I want to avoid the layer-break area therefore I need to write a dummy file (or recovery files, which is more useful) to that area to fill almost entire disc capacity .