I called it data container because of its name. I always used named volumes or bind mounts, but I know some peiple just ran a container with its anonymous volumes defined in the Docker image and used the “volumes-from” parameter to mount all the volumes from that container to an other container. I don’t exactly know what. Maybe it was used before named volumes was implemented (if it was not always there) or there was some other benefits. In the case of the zabbix containers, I don’t see any reference to that container, so for me it does not make sense. I guess yo could ask the maintainer of the image on GitHub.
It does not contain anything. As you noticed, it is just a busybox container that mounts a folder and does nothing with it.
Yes, this is the point. That container does nothing, so you will not see any logs. But you can see the logs of the other containers.
Whether a stopped/exited container is normal or not it depends on the actual project. Some containers just helper containers or init containers. They do something and stop. When you run the compose project again, they start again and stop. It can be used to fix file permissions or owners on the host so an other container can mount that folder from the host. Again, in this case, that container does nothing. Since nothing refers to the container, it is not a dependency of any container, it is not even guaranteed that this container will start before other containers. It is very likely though, because it does nothing and doing nothing can be done very fast 