Another customer was asking me a question over email with respect to referenced files. I thought I would include some information here because Photos handles referenced files differently from Aperture (basically, it’s identical to iPhoto):
– Photos supports images located on external drives (mixed with ones on the drive holding the photo library itself).
– These externally located files are called “referenced files”
– Thus, you can store the library on the internal drive, but store as many of the original files on the external drive.
– The edit information and full-size JPEGs are stored on the internal drive with the library.
– Albums and folders can include referenced files.
– The only time you would need the external drive is when you are editing an image.
– Referenced files are not uploaded to iCloud Photo library
– Photos cannot move a file from the internal location to an external location, nor can it move it from one external location to another.
– this is a problem if you run out of space on your external drive and want to relocate all the files to a new, larger drive.
That last point is the most important one – you cannot move files around as you could with Aperture.