2 system libraries for Photos using iCloud

Ad 2) Same Apple-ID on two different local macOS accounts → Works fine! 👍

• Involved an iPhone and two local mac user accounts all using the same Apple ID.
  • On the Mac one user is my regular user, which uses plenty of iCloud services. For iCloud Photos its system photo library uses "optimized" on the internal storage.
  • On the Mac the auxiliary / backup account uses ONLY one iCloud services which is iCloud Photos with its system photo library using "Originals" residing on an external volume.
• I created new content on all 3 accounts on all 2 devices and it synced fine in all directions.
  • And the "Optimized" library is by tendency smaller. As soon as you open items in it (it fetched the high quality) and then gets almost the same size (as long as enough storage/cache is available). But before opening videos, the "Optimized" library is clearly smaller.

So what works in this small test setup (with a few photos and videos) 🙂 shall also work on a large scale (with 60k media items using ca 400GB). I will give it a go soon 😉 .

No. There can only be one System Photo Library per user account on a Mac. You could have a second user account on your MBP singed into iCloud with the same Apple ID and with a library on an external drive. This library can be the System Photo Library for that user account and not have "Optimize Mac Storage" enabled. It would contain all of the full sized originals. Remember any changes to one library, i.e. edits, changes, additions or deletions will be reflected in the other library.

How big is your library? If a 1 TB SSD would handle it OK with room to grow (un-optimized) then you might consider having only one library, an un-optimized library on an external SSD like this one: 1TB OWC Envoy Pro mini 

You soiled have to have both your internal drive and the EHD backed up regularly by Time Machine.

Addendum: some users have a smaller ad un-optimized library on their internal drive that is not an iCloud library with just their favorite photos. Photos can be moved between the two libraries as needed. Just some food for thought.

Anyone who successfully used any of the following setups?

1) One macOS user account with two alternate (main) photo Libraries, one "optimized" on internal storage and one with "originals" residing on a large external drive?

• a) /Users/main-user/Pictures/Photo-Library-Optimized.photoslibrary using iCloud Photos with "Optimized Mac Storage"
• b) /Users/main-user/ using iCloud Photos with "Download Originals to this Mac" on /Volumes/Eternal-Storage/Photos-Library-Full.photoslibrary

My preliminary research showed the potential problem with this is that this is only possible as a "oneshot" as you can only have one main library.

• If you switch from A to B first time it downloads and saves everything. (Initial "oneshot")
• If you apply no changes on library B (merely acting as a "full backup library"), then switch back to A, and designate it as your main library: Does sync work correctly? No undesired dupes or deletions?
• If 3 months later, you want to run a "full backup to external storage" again and therefore you switch again from A to B, does it sync everything from to B which has changed centrally since then?
• This would be the simplest solution, as it requires only 1 Apple-ID and 1 macOS-user-account and 2 libraries (1 bound to internal storage, 1 bound to external storage).
  • But does this work reliably? Or error prone?
  • Any Apple/iCloud server side restrictions which may intervene? (error messages like "Not allowed. Already connected")

2) Same Apple-ID on two different local macOS accounts:

• /Users/main-user/Pictures/Photos-Library.photoslibrary using iCloud Photos with "Optimized Mac Storage"
• /Users/main-user-auxillary/ with main photos library residing on /Volumes/External-Storage/Photos-Library-Full.photoslibrary using iCloud Photos with "Download Originals to this Mac".

3) Two family members each accessing the same shared family library (one "optimized" on internal storage, the other "optimized" on external storage):

• User(s) with a single main Photos library using iCloud Photos with "Optimized Mac Storage"
  • /Users/dad/Pictures/Photos-Library.photoslibrary (possibly a subset of the superset)
  • /Users/mom/Pictures/Photos-Library.photoslibrary (possibly a subset of the superset)
• User with a single main Photos library using iCloud Photos with "Download Originals to this Mac" residing on external storage.
  • /Users/kid/ with main photos library (superset) residing on /Volumes/Eternal-Storage/Photos-Library-Full.photoslibrary

I haven't done this, but I'm not sure why it wouldn't work: First, create a new Apple ID -- you get 5 GB of iCloud storage, and this will keep you from messing up your iCloud Photos on your current ID.

Then make a small Library, a few hundred pictures, maybe, and make it your system Library for that account. Once it is populated into iCloud, switch iCloud off on that Library and create another one with the same name on an external library and make it your System Library on this new account. Photos should make this identical to the first Library, with the same few hundred pictures. Maybe add a few new pictures. Then switch back, making the original one your System Library, again, and turning on iCloud, and see if you get the new pictures in this Library, too.

I think that you can switch back and forth at will, and Photos will keep making each one identical to the iCloud version. If this is with a new ID, then you won't have anything to lose with the experiment.

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