In my experiements on running Jenkins on Docker, I wondered how the volumne worked when I provided-v to the run command.

I found a great article which succintly explains a lot about the Docker Volume - which will be handy for any docker beginer.

Original article ishere

My summary goes below:

• Docker Volume is the way topersist data between container restarts andshare it between containers.
• A volume is stored on the host file system. Usually within obscure directories inside/var/lib/docker. However, a specific directory on host system can also be mounted as volume in a container.
• Volumes can be managed usingdocker volume and its sub commands.
• Docker won't delete volume unless specifically instructed to do so. This can result in stale data on the host system. So tidying up once in a while might come handy.
• Important Caveat - Don't try to modify the content of the volume in the Dockerfile (via RUN) as each build step creates anew volume and your changes will be discarded. If you want to change the volume content, do so using theENTRYPOINT command in the Dockerfile. Have a look at thislink.
• If you are looking for a thorough overview of different approaches to manage application data, including the use ofVolume, Bind mounts, tmpfs mounts, read thislonger article

Image Credit:https://docs.docker.com/engine/admin/volumes/images/types-of-mounts-volume.png