iCloud wants to duplicate 300GB of photos!
Q When the new Photos app arrived, I was happy to move from Aperture because I wanted to make use of the options to store all my photos in iCloud – both to have an off-site backup, and also to have access to all my pictures across all my iOS devices. It took around a week to upload all 300GB of photos and videos, but the convenience and security were worth it.
I had an annoying problem with the HDD and decided to clone and erase the disk then copy across the files and folders back onto it. I named it the same as before, and dragged the files and media back. The Photos library opened just fine, but now the app thought it was a brand new set of photos and offered to upload them all to iCloud – again.
In the end, I had to delete the library on my HDD, open Photos with no library selected, and then download the photos from iCloud within the app – all for a set of photos I already had a copy of! Tim van Someren
A I haven’t been able to absolutely confirm this, but it looks like Photos might be saving the full path to each image when it uploads them to iCloud, including the UUID label of the disk volume. This could be necessary to allow you to back up the photo libraries from multiple Macs to the same iCloud account. The libraries on two Macs would have the same path name by default, but the UUID would differ so the backups wouldn’t overwrite. But erasing your disk and reformatting it means it gets assigned a new UUID, so iCloud treats the restored files as new copies in a different location.
Cloning the drive back again, instead of just dragging the folders across, would restore the original UUID but might conceivably mean you’d recreate whatever problem you had. The SuperDuper! backup utility (www.shirt-pocket.com) has a secret command-line tool that will let you force the UUID of a volume to whatever you like, so you could use this to restore the UUID to the previous value. But this is pretty technical and only works if you have made a note of the previous UUID name of the volume. I think cloning the drive back is the only practical way to avoid iCloud uploading everything again.
iCloud can end up duplicating your photos if you erase your library and copy everything back.