How does Automatic Seeding work - Always On Availability Group
As you noted, the docs refer to &quot;log stream transport&quot; when performing automatic seeding. Similar to the way that you can stream movies to your device without downloading a specific file, automatic seeding streams data to the secondary without storing an actual backup file.
While the technical implementation details aren't exactly this, it's essentially taking a backup, but rather than sending it to a storage device or file share, it sends it to the secondary server. Rather than writing a file, it immediately begins to restore to the secondary server. The pseudo-backup is buffered and restored in a single step, without a literal backup being written to file.