The official answer is available in the section “Back up, restore, or migrate data volumes”:
BACKUP:
sudo docker run --rm --volumes-from DATA -v $(pwd):/backup busybox tar cvf /backup/backup.tar /data
--rm
: remove the container when it exits--volumes-from DATA
: attach to the volumes shared by the DATA container-v $(pwd):/backup
: bind mount the current directory into the container; to write the tar file tobusybox
: a small simpler image – good for quick maintenancetar cvf /backup/backup.tar /data
: creates an uncompressed tar file of all the files in the /data directory
RESTORE:
# create a new data container
$ sudo docker create -v /data --name DATA2 busybox true
# untar the backup files into the new container᾿s data volume
$ sudo docker run --rm --volumes-from DATA2 -v $(pwd):/backup busybox tar xvf /backup/backup.tar
data/
data/sven.txt
# compare to the original container
$ sudo docker run --rm --volumes-from DATA -v `pwd`:/backup busybox ls /data
sven.txt