I do want to talk a bit more about things I’ve discovered about Photos since my initial discovery. After the transition to Photos from Aperture, SuperDuper!, which I use for my local backups, told me that my 1TB backup drive couldn’t accommodate my 850GB of data. When you run the migration from iPhoto/Aperture to Photos, it creates a new library file that looks like it’s a complete duplicate of all of your photos, thereby doubling the disk space chewed up by photos. However, the two databases use hard links to a single set of files, so in fact it’s not a true duplicate.
I suspected that the problem might be that SuperDuper! was viewing the old library and the new library as duplicates of the data. I tried searching in their help files for an answer but Apple’s insistence on calling things by their generic names (like Photos), it makes it REALLY hard to use search pretty much anywhere.
I wrote to support at shirt-pocket.com and they got back to me immediately that all I had to do was delete my backup and start from scratch and it would get sorted. A few hours later I was back in business.
Then I noticed that my offsite backup to CrashPlan was doing the same thing When I wrote to them (and they also got back to me immediately) they said to just let it ride and it would get sorted as well and it eventually did finish after a couple of days. It is still showing nearly a TB of backups while I’m backing up far less than that. I’m not sure if it’s so big because they keep history for you or because they’re still storing a duplicate copy of the photos, but it doesn’t really matter to me since they don’t charge by data storage.
Just remember, that when you do make the switch backups could get weird at first, but don’t panic. Contact your backup vendor and ask them the best way to move forward. Now that I think about it, I wonder if Time Machine is smart enough to handle this correctly?