A complex set of rules with optional flags determines whether any given xattr is preserved when copying, saving, syncing with a cloud service, backing up, and more. Here they are.
extended attributes
Information about the data in a file can be found in different places: in the file’s attributes, in extended attributes that tend to be Mac-only, and embedded with the data, as in EXIF.
Adding your own custom icons to files and folders goes back a long way, to Classic Mac OS […]
Finder tags should sync in iCloud Drive, and should be found when you use Spotlight search for their tag labels. Here’s what to check when there are problems.
When do sparse files explode to full size, and how could you preserve them in transit? Can you copy clones or snapshots? How to preserve extended attributes?
If you have Optimise Mac Storage enabled for iCloud Drive, this new feature lets you pin the files you want to be stored locally and not evicted. Full details.
macOS has an elaborate set of rules determining which types of xattr are preserve during different types of copying, including syncing to iCloud Drive. Here they are in full detail.
Extended attributes were added to Mac OS X 10.4, and soon supported the quarantine xattr. They have since flourished, and have valuable properties.
How the resource forks of Classic Mac OS became extended attributes in Mac OS X 10.4, then flourished. How clone files handle xattrs, and which are used by APFS itself.
Understanding how APFS works: inodes, attributes, file extents, extended attributes, and how they change with editing and cloning.
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