Updates to Files On-Demand on macOS

Grimrian The plain AFP framework creates a file location (sort of a virtual disk) for each service that shows in Finder just below the computer in the storage tree. The actual directory (file database) lives in ~/Library/CloudStorage, where ~ is the user’s home folder (I may have bunged up the exact folder name). That “shadow folder” stores both cached (temporary local storage) files and placeholders for cloud only files. The AFP framework manages file requests by serving either the cached file or retrieving the file from the cloud to the cache. It also manages syncing the most recent versions to and from the cloud. 

Because ~/Library is on your system drive, any cached files take up system drive space, which shoots the idea of an external storage drive to hell, and Apple provides no way to relocate the cache to an external drive. I’d even be happy if they kept just an index (a list of files with pointers to their actual locations) on the system drive and the actual cache externally. 

That is basically what Microsoft’s external storage hack does. It keeps the shadow folder in ~/Library for AFP to use, but rather than keeping the actual files there, it adds a second layer of redirection to a cache on an external drive. If a file is cached on the external drive, OneDrive serves that to AFP, which in turn serves it to the requesting program. I don’t know the exact internal process, but I believe that’s an accurate overview. 

Where the OneDrive process gets funky is that it appears to store some locally cached files in ~/Library instead of the external drive, although that can be hard to tell, because -nix operating systems can make a file pointer look a lot like an actual file. With the added layer of abstraction, OneDrive also has a hard time setting the cloud storage icon correctly, so it’s hard to know if a file is stored locally, in the cloud, or is syncing. The one thing that is fairly simple is that if you look at the hidden cache directory on your external drive, locally cached files are just regular files that can be backed up or opened, although that will probably bung up OneDrive. 

Make sense?