Im very happy with the sandisk wireless media drive 64 gb. Specially since my ipad air is only 16gb.....this takes care of all my storage problems. I use the drive to load pdfs which i transfer to ibooks without opening itunes. My question....if i connect to itunes with my ipad, for a sw update or a backup, what will happen if i hit the sync button.....will it erase all the pdfs i transferrred from my sandisk drive or will it add them to itunes. I do not want the latter to happen. Am i better off just leaving the sync button alone?