How do I fix the duplicate libraries I think the new Photos app has made? I used to use iPhoto, and my photo library was around ~40GB+ in size. When I upgraded to Yosemite, I was forced to use the "Photos" app which "migrated" my photos.

When I open my home folder. The "Pictures" folder is ~130GB+ in size! When I open it I see:


  iPhoto Library - 44.81GB (Migrated Photo Library) Photos Library 2 -
  44.51GB (Photos Library) Photos Library.photoslibrary_prepare - 43.85GB (Folder)


I can't use iPhoto anymore because Yosemite doesn't let me. I have time machine backups. I just want to delete the duplicate library, but I don't know how to verify that they are indeed duplicates, or somehow connected to Photos. I want to still be able to access my photos on my mac. I used to use Aperture as well, but Yosemite has rendered it useless.

What is the best way to clean up the duplicates (if they really are duplicates), without losing my photos ? I'm fine "using" the Photos "App". :(

EDIT:

I deleted iPhoto Library and Photos Library.photoslibrary_prepare.
I emptied my trash after that.

I opened photos, and it seems to be working. Nothing seems to be missing. But the amount of free space I have on my hard drive has increased only by 10GB. Weird.. No idea whats going on. Can't tell what Photos has done. 

Any idea what's going on ?

EDIT: The amount of free space has going back to its original amount, even though I just "deleted" 80GB+ of photos... 

EDIT: After restarting my mac, there appears to be ~8GB more of space. If I add up the sizes of all the folders under "Macintosh HD", there should be 110GB of free space (out of 500GB), but OS X reports only 77GB free. So where is the missing 33GB?
See https://apple.stackexchange.com/a/180313/54484

The files were not duplicated, rather additional hard links were created. The data exists once, and each hard link is simply a pointer to that data on the hard drive.

Deleting one library will not recover any significant space, because hard links to the same data still exist. Finder shows the size for each library bundle as including the hard linked files, so it appears that much more space is being used, when it is in fact not.

As far as your "missing" 33 GB, unless you have turned on the display of hidden folders you are not getting an accurate count by simply counting the size of visible folders. Use something like Daisy Disk for a true view of what space is being taken up and where.

Finally, for the record, both Aperture and iPhoto work fine under Yosemite, so long as you don't delete the libraries they used. They cannot read a Photos format library.