This works as long as you have enough storage locally. Our photo library is ~3TB split over 2 users, and while you could theoretically use an external SSD for storage, that kinda cuts down on mobility. You could leave the drive attached and drag it around, or detach it and lose access to your photos on the go.
For a long time, I had a Mac mini running 24/7, where each user was logged in (via Remote Desktop), and that would synchronize photos to an external drive, and the Mac would then make backups (via Arq) to my NAS as well as a remote location.
I don’t count the Mac copy in my 3-2-1 as it is basically sync (each side, iCloud and Mac, are sync), and without versioning, ie APFS snapshots, if one side goes bad, so does the other.
I’ve since switched to using Parachute for day to day backups, and every ~6 months I make a manual full export of the photo library in case Parachute missed something.
For a long time, I had a Mac mini running 24/7, where each user was logged in (via Remote Desktop), and that would synchronize photos to an external drive, and the Mac would then make backups (via Arq) to my NAS as well as a remote location.
I don’t count the Mac copy in my 3-2-1 as it is basically sync (each side, iCloud and Mac, are sync), and without versioning, ie APFS snapshots, if one side goes bad, so does the other.
I’ve since switched to using Parachute for day to day backups, and every ~6 months I make a manual full export of the photo library in case Parachute missed something.