Here is what i tried and seems to be working ok but probably requires a bit more testing so before you try this by yourself with your default Photos Library, maybe create a new Photos Library for testing purposes: Adjust the size of your Photos library to work with iCloud Photo Library - Apple Support
You can create a new Photos library to use with iCloud Photo Library. (...)
- Hold down the Option key while opening Photos.
- Choose Create New.
- Import content from your previous library to create a new, smaller library.
Also, it won't be a bad idea to create a Time Machine Backup before you start messing with your photos. In case if something would go wrong, you can restore your library to the previous state: Mac Basics: Time Machine backs up your Mac - Apple Support
Here are the steps:
1. Use Disk Utility to create a Sparse Bundle Disk Image (Image grows in size when you are putting files in it but the catch is that you need to defined the maximum size of the Sparse Bundle when you are creating this image). To do that, open Disk Utility app and go to File > New > Blank Disk Image: Disk Utility 12.x: Create a disk image
For my testing i have used these settings for new Spars Bundle Disk Image:
Saves as: Photos Shared Library
Where: /Users/Library
Name: Photos Shared Library
Size: Custom (10 GB)
Format: Mac Os Extended (Journaled)
Encryption: None
Partitions: Single partition - GUID Partition Map
Image Format: sparse bundle disk image
2. Make sure that all users which should have access to Photos Shared Library have Read and Write access to Shared folder: Mac Basics: File Sharing - Apple Support
and that the /Users/Shared folder privileges are applied to enclosed items:
3. Mount (if it's not mounted yet) Photos Shared Library in Finder, open it and move your Photos Library to it: OS X Yosemite: Folder basics
4. Now, to make sure Photos app will open correct Photos Library (each time when application is open), you need to make sure that after each user will log in to his account Photos Shared Library Sparse Bundle is automaticaly mounted. The easiest way to do that is to add Photos Shared Library Sparse Bundle to Login Items and this needs to be done on each user account: OS X Yosemite: Open items automatically when you log in
Now... I did not test this setup for a long period but i am able to view/edit/add/remove photos and it seems to be working ok. Perhaps, if you have more time and would like to give it a try, you could share your thoughts.
Things that you will need to remeber with this setup:
- Now, with this setup you problably would have to disable photos in your iCloud Preferences Pane and forget about using this service and what is going with it (My Photo Stream and iCloud Photo Sharing). Unless on each user account you are signed in with the same Apple ID then you could test this setup and see how that will work for you.
- You can't use fast user switching. Only one user can use Photos Library at the time. What this mean is that you will need to make sure that one user is fully logged out before another user can log in to his account.