--- description: Using volumes title: Use volumes keywords: storage, persistence, data persistence, volumes redirect_from: - /engine/tutorials/dockervolumes/ - /engine/userguide/dockervolumes/ - /engine/admin/volumes/volumes/ --- Volumes are the preferred mechanism for persisting data generated by and used by Docker containers. While [bind mounts](bind-mounts.md) are dependent on the directory structure of the host machine, volumes are completely managed by Docker. Volumes have several advantages over bind mounts: - Volumes are easier to back up or migrate than bind mounts. - You can manage volumes using Docker CLI commands or the Docker API. - Volumes work on both Linux and Windows containers. - Volumes can be more safely shared among multiple containers. - Volume drivers allow you to store volumes on remote hosts or cloud providers, to encrypt the contents of volumes, or to add other functionality. - A new volume's contents can be pre-populated by a container. In addition, volumes are often a better choice than persisting data in a container's writable layer, because using a volume does not increase the size of containers using it, and the volume's contents exist outside the lifecycle of a given container. ![volumes on the Docker host](images/types-of-mounts-volume.png) If your container generates non-persistent state data, consider using a [tmpfs mount](tmpfs.md) to avoid storing the data anywhere permanently, and to increase the container's performance by avoiding writing into the container's writable layer. Volumes use `rprivate` bind propagation, and bind propagation is not configurable for volumes. ## Choose the -v or --mount flag Originally, the `-v` or `--volume` flag was used for standalone containers and the `--mount` flag was used for swarm services. However, starting with Docker 17.06, you can also use `--mount` with standalone containers. In general, `--mount` is more explicit and verbose. The biggest difference is that the `-v` syntax combines all the options together in one field, while the `--mount` syntax separates them. Here is a comparison of the syntax for each flag. > **Tip**: New users should use the `--mount` syntax. Experienced users may > be more familiar with the `-v` or `--volume` syntax, but are encouraged to > use `--mount`, because research has shown it to be easier to use. If you need to specify volume driver options, you must use `--mount`. - **`-v` or `--volume`**: Consists of three fields, separated by colon characters (`:`). The fields must be in the correct order, and the meaning of each field is not immediately obvious. - In the case of named volumes, the first field is the name of the volume, and is unique on a given host machine. For anonymous volumes, the first field is omitted. - The second field is the path where the file or directory are mounted in the container. - The third field is optional, and is a comma-separated list of options, such as `ro`. These options are discussed below. - **`--mount`**: Consists of multiple key-value pairs, separated by commas and each consisting of a `=` tuple. The `--mount` syntax is more verbose than `-v` or `--volume`, but the order of the keys is not significant, and the value of the flag is easier to understand. - The `type` of the mount, which can be [`bind`](bind-mounts.md), `volume`, or [`tmpfs`](tmpfs.md). This topic discusses volumes, so the type is always `volume`. - The `source` of the mount. For named volumes, this is the name of the volume. For anonymous volumes, this field is omitted. May be specified as `source` or `src`. - The `destination` takes as its value the path where the file or directory is mounted in the container. May be specified as `destination`, `dst`, or `target`. - The `readonly` option, if present, causes the bind mount to be [mounted into the container as read-only](#use-a-read-only-volume). - The `volume-opt` option, which can be specified more than once, takes a key-value pair consisting of the option name and its value. The examples below show both the `--mount` and `-v` syntax where possible, and `--mount` is presented first. ### Differences between `-v` and `--mount` behavior As opposed to bind mounts, all options for volumes are available for both `--mount` and `-v` flags. When using volumes with services, only `--mount` is supported. ## Create and manage volumes Unlike a bind mount, you can create and manage volumes outside the scope of any container. **Create a volume**: ```bash $ docker volume create my-vol ``` **List volumes**: ```bash $ docker volume ls local my-vol ``` **Inspect a volume**: ```bash $ docker volume inspect my-vol [ { "Driver": "local", "Labels": {}, "Mountpoint": "/var/lib/docker/volumes/my-vol/_data", "Name": "my-vol", "Options": {}, "Scope": "local" } ] ``` **Remove a volume**: ```bash $ docker volume rm my-vol ``` ## Start a container with a volume If you start a container with a volume that does not yet exist, Docker creates the volume for you. The following example mounts the volume `myvol2` into `/app/` in the container. The `-v` and `--mount` examples below produce the same result. You can't run them both unless you remove the `devtest` container and the `myvol2` volume after running the first one.
```bash $ docker run -d \ --name devtest \ --mount source=myvol2,target=/app \ nginx:latest ```
```bash $ docker run -d \ --name devtest \ -v myvol2:/app \ nginx:latest ```
Use `docker inspect devtest` to verify that the volume was created and mounted correctly. Look for the `Mounts` section: ```json "Mounts": [ { "Type": "volume", "Name": "myvol2", "Source": "/var/lib/docker/volumes/myvol2/_data", "Destination": "/app", "Driver": "local", "Mode": "", "RW": true, "Propagation": "" } ], ``` This shows that the mount is a volume, it shows the correct source and destination, and that the mount is read-write. Stop the container and remove the volume. ```bash $ docker container stop devtest $ docker container rm devtest $ docker volume rm myvol2 ``` ### Start a service with volumes When you start a service and define a volume, each service container uses its own local volume. None of the containers can share this data if you use the `local` volume driver, but some volume drivers do support shared storage. Docker for AWS and Docker for Azure both support persistent storage using the Cloudstor plugin. The following example starts a `nginx` service with four replicas, each of which uses a local volume called `myvol2`. ```bash $ docker service create -d \ --replicas=4 \ --name devtest-service \ --mount source=myvol2,target=/app \ nginx:latest ``` Use `docker service ps devtest-service` to verify that the service is running: ```bash $ docker service ps devtest-service ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS 4d7oz1j85wwn devtest-service.1 nginx:latest moby Running Running 14 seconds ago ``` Remove the service, which stops all its tasks: ```bash $ docker service rm devtest-service ``` #### Syntax differences for services The `docker service create` command does not support the `-v` or `--volume` flag. When mounting a volume into a service's containers, you must use the `--mount` flag. ### Populate a volume using a container If you start a container which creates a new volume, as above, and the container has files or directories in the directory to be mounted (such as `/app/` above), the directory's contents are copied into the volume. The container then mounts and uses the volume, and other containers which use the volume also have access to the pre-populated content. To illustrate this, this example starts an `nginx` container and populates the new volume `nginx-vol` with the contents of the container's `/usr/share/nginx/html` directory, which is where Nginx stores its default HTML content. The `--mount` and `-v` examples have the same end result.
```bash $ docker run -d \ --name=nginxtest \ --mount source=nginx-vol,destination=/usr/share/nginx/html \ nginx:latest ```
```bash $ docker run -d \ --name=nginxtest \ -v nginx-vol:/usr/share/nginx/html \ nginx:latest ```
After running either of these examples, run the following commands to clean up the containers and volumes. ```bash $ docker container stop nginxtest $ docker container rm nginxtest $ docker volume rm nginx-vol ``` ## Use a read-only volume For some development applications, the container needs to write into the bind mount so that changes are propagated back to the Docker host. At other times, the container only needs read access to the data. Remember that multiple containers can mount the same volume, and it can be mounted read-write for some of them and read-only for others, at the same time. This example modifies the one above but mounts the directory as a read-only volume, by adding `ro` to the (empty by default) list of options, after the mount point within the container. Where multiple options are present, separate them by commas. The `--mount` and `-v` examples have the same result.
```bash $ docker run -d \ --name=nginxtest \ --mount source=nginx-vol,destination=/usr/share/nginx/html,readonly \ nginx:latest ```
```bash $ docker run -d \ --name=nginxtest \ -v nginx-vol:/usr/share/nginx/html:ro \ nginx:latest ```
Use `docker inspect nginxtest` to verify that the bind mount was created correctly. Look for the `Mounts` section: ```json "Mounts": [ { "Type": "volume", "Name": "nginx-vol", "Source": "/var/lib/docker/volumes/nginx-vol/_data", "Destination": "/usr/share/nginx/html", "Driver": "local", "Mode": "", "RW": false, "Propagation": "" } ], ``` Stop and remove the container, and remove the volume: ```bash $ docker container stop nginxtest $ docker container rm nginxtest $ docker volume rm nginx-vol ``` ## Use a volume driver When you create a volume using `docker volume create`, or when you start a container which uses a not-yet-created volume, you can specify a volume driver. The following examples use the `vieux/sshfs` volume driver, first when creating a standalone volume, and then when starting a container which creates a new volume. ### Initial set-up This example assumes that you have two nodes, the first of which is a Docker host and can connect to the second using SSH. On the Docker host, install the `vieux/sshfs` plugin: ```bash $ docker plugin install --grant-all-permissions vieux/sshfs ``` ### Create a volume using a volume driver This example specifies a SSH password, but if the two hosts have shared keys configured, you can omit the password. Each volume driver may have zero or more configurable options, each of which is specified using an `-o` flag. ```bash $ docker volume create --driver vieux/sshfs \ -o sshcmd=test@node2:/home/test \ -o password=testpassword \ sshvolume ``` ### Start a container which creates a volume using a volume driver This example specifies a SSH password, but if the two hosts have shared keys configured, you can omit the password. Each volume driver may have zero or more configurable options. **If the volume driver requires you to pass options, you must use the `--mount` flag to mount the volume, rather than `-v`.** ```bash $ docker run -d \ --name sshfs-container \ --volume-driver vieux/sshfs \ --mount src=sshvolume,target=/app,volume-opt=sshcmd=test@node2:/home/test,volume-opt=password=testpassword \ nginx:latest ``` ## Next steps - Learn about [bind mounts](bind-mounts.md). - Learn about [tmpfs mounts](tmpfs.md). - Learn about [storage drivers](/storage/storagedriver/).