# tested with a 1.5GB TIFF file that didn't fit into 8GB of memory, so disk space had to be used. All in all it took over about 8GB + 11GB of memory
mkdir ~/.magicktmp # make it where you have enough disk space
MAGICK_TMPDIR=~/.magicktmp convert huge.tif -crop 50%x100% +repage huge_%d.tif