Writing into a volume's mountpoint only restores it when the mountpoint is the storage. A volume with driver options - NFS, a bind device, tmpfs - keeps the same /var/lib/docker/volumes/<name>/_data path, but docker mounts the real backing store over it on demand and unmounts it again when the last consumer stops. Restoring while nothing holds it lands in the empty directory underneath, is hidden by the next mount, and rsync reports success.
The declaration decides, not the mount table: the driver and its options are true at every moment, where the mount table is only true while a container happens to hold the volume.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
