iPhoto library.migratediphotolibrary and iPhotolibrary.photoslibrary

Since iPhoto is not able to use iCloud Photo Library at all this has nothing to do with using iCloud Photo Library

Open each library using iPhoto and see what exactly they are - I suspect they are duplicates somehow but only you can figure that out - and if so then you do not need both (if you are for sure done with iPhoto you do not need either - but be sure to keep a good archive just in case)

LN

The first is your old iPhotos Library post-migration into Photos. The other is the Photos Library. Use Photos preferences to change the settings to store only in the cloud when there is no room on the drive.

Freeing Up Space on The Hard Drive

1. See Lion/Mountain Lion/Mavericks' Storage Display.

2. You can remove data from your Home folder except for the /Home/Library/ folder.

3. Visit The XLab FAQs and read the FAQ on freeing up space on your hard drive.

4. Also see Freeing space on your Mac OS X startup disk.

5. See Where did my Disk Space go?.

6. See The Storage Display.

You must Empty the Trash in order to recover the space they occupied on the hard drive.

You should consider replacing the drive with a larger one. Check out OWC for drives, tutorials, and toolkits.

Try using OmniDiskSweeper 1.8 or GrandPerspective to search your drive for large files and where they are located.

I have these two files

iPhoto library.migratediphotolibrary

iPhotolibrary.photoslibrary

You will see these two libarriess whenever you open an iPhoto Library in Photos. Photos will create a new library "iPhoto library.photoslibrary" and rename the original iPhoto Library to "iPhoto library.migratediphotolibrary". Both libraries will have about approximately the same size, but will actually be sharing the storage for the photos using hard links. It will only look like you were wasting storage on duplicates. the image files in both libraries are using the same files on the disk.

See these documents:

• Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support
• Six Colors: The (hard) link between Photos and iPhoto

Once you are sure, that you do not need your iPhoto library any longer, you should make a backup copy of iPhoto library.migratediphotolibrary, and then you can trash it. But you will not gain much storage back this way, because the image files are using the same storage as Photos is using.