How is docker image stored

Docker images use a hierarchical storage mechanism, each layer is a modified version of its parent layer, allowing the image to easily share the layer to save storage space. The image uses OCI standardized storage formats and is stored in the local host (/var/lib/docker/image) and in the Docker registry (such as Docker Hub).

Docker image storage mechanism

Docker images are templates for creating and running containers. They are stored in the Docker registry and can be pulled from the Docker Hub or other registry.

Docker image storage is hierarchical, each layer is a modified version of its parent layer. This allows images to easily share layers, saving storage space.

Storage format

Docker images use a standardized storage format called OCI (Open Container Initiative) mirroring specification. This format defines the file structure and content of the image.

Storage location

Docker images are stored in the following locations:

• Localhost: The pulled image is stored in the /var/lib/docker/image directory.
• Docker Registry: Mirrors can also be stored in Docker registry, such as Docker Hub.

Hierarchical mechanism

Docker images are organized into a series of layers, each layer being a modified version of its parent layer. These layers are stacked in order, the bottom layer is the base image, and the top layer is the latest modifications.

Each layer contains changes to the file system, such as adding or removing files. When a new image is created, it inherits all the underlying layers from the parent image and adds its own modification layer at the top of it.

Save space

The hierarchical storage mechanism saves storage space by allowing sharing the underlying layer. When multiple images share the same underlying layer, they only need to store their respective modification layers.

For example, if there is a Debian image based on it, and both images have Apache installed, they will share the same Debian underlying layer. Only the Apache tier will be different, saving storage space.

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