Day 28/40
Docker Volume Explained - Docker Bind Mount - Docker Persistent Storage
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@piyushsachdeva
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In this section, we're looking at docker storage, how it works behind the scene and how we can use storage in docker.
Assume we need to add a writable layer, container layer to our application, which is persist even it would be down or restarted after creation.
The container layer nothing but the writable copy of Read-only layer but it's not persistent.
So with the help of volume we can have persistent data for a container.
Storage drivers is responsible for writing data in container layer. It also stores layers within container
Volume drivers is responsible to make the data persistent.
The Docker Engine provides the following storage drivers on Linux:
| Driver | Description |
|---|---|
overlay2 |
overlay2 is the preferred storage driver for all currently supported Linux distributions, and requires no extra configuration. |
fuse-overlayfs |
fuse-overlayfsis preferred only for running Rootless Docker on an old host that does not provide support for rootless overlay2. The fuse-overlayfs driver does not need to be used since Linux kernel 5.11, and overlay2 works even in rootless mode. Refer to the rootless mode documentation for details. |
btrfs and zfs
|
The btrfs and zfs storage drivers allow for advanced options, such as creating "snapshots", but require more maintenance and setup. Each of these relies on the backing filesystem being configured correctly. |
vfs |
The vfs storage driver is intended for testing purposes, and for situations where no copy-on-write filesystem can be used. Performance of this storage driver is poor, and is not generally recommended for production use. |
Creating a volume in docker
root@localhost:~# docker volume create data_vol
data_vol
root@localhost:~# docker volumes
docker: 'volumes' is not a docker command.
See 'docker --help'
root@localhost:~# docker volume ls
DRIVER VOLUME NAME
local data_vol
root@localhost:~# ls -lh /var/lib/docker/volumes/data_vol/
total 4.0K
drwxr-xr-x 2 root root 4.0K Aug 1 15:08 _data
root@localhost:~# ls -lh /var/lib/docker/volumes/data_vol/_data/
total 0
Mount new volume to a container
root@sinaops:~# docker run -v data_vol:/app -dp 3000:3000 --name todo day02-todo
4c4a22dfd59e4b956eadc464ac93a64db1bfcbb3c23580e55a46b24ea8431091
root@sinaops:~# ls -lh /var/lib/docker/volumes/data_vol/_data/
total 164K
-rw-r--r-- 1 root root 269 Aug 1 14:37 README.md
drwxr-xr-x 167 root root 4.0K Aug 1 15:23 node_modules
-rw-r--r-- 1 root root 648 Aug 1 14:37 package.json
drwxr-xr-x 4 root root 4.0K Aug 1 15:23 spec
drwxr-xr-x 5 root root 4.0K Aug 1 15:23 src
-rw-r--r-- 1 root root 144K Aug 1 14:37 yarn.lock
root@sinaops:~# du -s /var/lib/docker/volumes/data_vol/_data/
28196 /var/lib/docker/volumes/data_vol/_data/
After restarting the container, the data will be persistent.
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