If you have not already taken the plunge and updated to Photos.app... just don't. At least not before you make a copy of your iphoto library and store it on another drive where photos.app can't get at it. That way, at least, you'll be able to restore your library and continue with iPhoto/Aperture. Photos.app is an abomination. Most of the features have been removed. You cannot open your images in any other application for editing (no Photoshop, Acorn, Pixelmator, Nik). You cannot change the user interface to avoid all that white. and the editing tools are just iOS related. You do, at least, still get the choice NOT to use icloud photos for storage. Once you upgrade to Yosemite, your installs of iPhoto and Aperture remain intact. But your photo library will not... it will still be readable by those other apps after you migrate it to Photos, but you wont be able to edit, anymore... anything you do edit will not be translated back to Photos.app. Its become a really closed shop and I do not recommend it or like it.