How does Photos transfer full-resolution originals from iCloud to Shared Albums with Optimise Mac Storage?

I am using Photos on macOS 27.0.1 with Optimise Mac Storage enabled. My photos are already synchronised to iCloud Photos, but some full-resolution originals are stored only in iCloud, with optimised versions on my Mac. When I create a new Shared Album using these photos, does Photos need to download the full-resolution originals to my Mac before uploading them again to the Shared Album, or can Apple transfer them directly between iCloud Photos and Shared Albums on its servers? Since the new Shared Albums support full-resolution photos and count towards iCloud storage, I would also like to know whether this process temporarily consumes additional local disk space and download/upload bandwidth, and how I can confirm that all photos have finished uploading and are ready for sharing.

Posted on Oct 18, 2026 4:34 PM

1 reply

Richard.Taylor

Level 7 (25,466 points)

Oct 19, 2026 7:29 AM in response to Ivan H

Ivan H wrote: does Photos need to download the full-resolution originals to my Mac before uploading them again to the Shared Album, or can Apple transfer them directly between iCloud Photos and Shared Albums on its servers?

I'm not totally sure, but it looks like Shared Albums now are just links to iCloud.

I would also like to know whether this process temporarily consumes additional local disk space and download/upload bandwidth,

Everything you do uses local storage to temporarily manipulate files. If you run low on storage, then those operations may not be able to be completed and, ironically, that can mean that even deleting doesn't work. If you have less than 10% of your Mac's storage free and available, then things can get lost forever. This is also true if your iCloud storage space gets low.

On my 1TB MacAir, I have seen strange things when freed storage got below 15%. 100GB free was not enough, and things cleared up when I got 150GB free. There really isn't any away around this. If you need extra space, then with a Mac mini, it's easy (but not cheap, anymore) to add an external drive.