Hi,
Show ASUS has only approved 7mm thickness 2.5-inch drives for the GL504GW, so safer to stick to that if you don't want to have any problems, but not sure what will happen if you try a 9.5mm thickness drive on this unit (it may not fit).
Also, if everyone didn't know, the 2.5-inch drives require an extra HDD cable or fpc to plug into the GL504GW motherboard since you cannot plug the drive directly into the motherboard, so you may want to make sure you can find that in your accessory box or figure out a way to get one if you need it.
Thanks.