dubthedankest wrote:
Where are the masters actually stored upon conversion from Aperture to Photos? Photos?
The master files are stored on your drive, but they are not actually stored "in" any folder. Folders are really just special files that store various bits of information about the files associated with that folder, including links to where they actually are stored. That's why you can "move" a file from one folder to another very quickly: all that you really are doing is moving the link & other info from one folder to the other folder, while the file itself stays where it was.
Because of this, it is possible for more than one folder to link to the same file -- in the Finder it looks just like there are two copies of the file, one in each folder, but there really is just the one copy. From the description in the Photos saves disk space by sharing images with your iPhoto or Aperture libraries doc, it looks like that's what happens when you import your iPhoto library into Photos -- both the old iPhoto Library "file" (which actually is a set of folders & subfolders of files) & the Photos Library (also consisting of folders & files) contain links to the master files, but like the Apple doc says, there really is just one set of master files being stored.
This is very similar to the way Time Machine backups look like they have multiple copies of the same unique file, one in each time-stamped backup folder, but there really is only one copy on the Time Machine drive. My guess is Apple is using hard links for this, which means the actual master files will not be deleted from the file system as long as at least one link remains to each of them.
So you should be safe in deleting the old iPhotos Library once you are absolutely sure you don't need it, but to be sure, if it was me I would make a backup just in case, or better yet just leave it alone.