MyBook temperature and location

i have 2 Mybook USB 2, connect to my MAC

i need to move them in a smaller spaace, where they have a shelf close to the top

but the still have air and space around

how do i know if the get too hot?

what would happen i i lay the disk on the side? and on witch side should i lay the disk?

The drive should not be hot to the touch. Nothing will happen if the drive is put horizontally. Either side will work as long as nothing is covering the conducts in which the drive gets air.