docker - docker 镜像的大小和虚拟大小有什么区别？

Question

我有一个私有(private)注册表，用于存储我的所有 docker 镜像。

我注意到，当我从中提取图像时，本地计算机上的图像大小与注册表上的图像大小差异很大。

例如，我有一个名为 mydb(大约 126 MB)的图像。

当我将它拉到我的本地机器上并执行 "docker images" 时，它会显示该图像的 "VIRTUAL SIZE"现在几乎是原来的三倍 (388 MB)。

我想知道这是什么原因以及“虚拟尺寸”的实际含义。

谢谢你:)。

Answer 1

你可以在这里找到对这个概念的一个很好的解释:https://github.com/docker/docker.github.io/issues/1520#issuecomment-305179362

来自 thaJeztah

The "size" and "virtual size" describe the amount of disk space used by a container. Let me try and explain:

When starting a container, the image that the container is started from is mounted read-only. On top of that, a writable layer is mounted, in which any changes made to the container are written.

The read-only layers of an image can be shared between any container that is started from the same image, whereas the "writable" layer is unique per container (because: you don't want changes made in container "a" to appear in container "b" smile)

Back to the docker ps -s output;

The "size" information shows the amount of data (on disk) that is used for the writable layer of each container The "virtual size" is the total amount of disk-space used for the read-only image data used by the container and the writable layer. The reason it's named "virtual size", is that (as described earlier), the disk space for the read-only layer(s) can be shared between containers, so only take up disk space once (perhaps a different name ("shared" size?) would have been better in hindsight, but naming is hard :) ) . edit: virtual actually shows the combined size of the readonly layer (the image), and the writable layer of the container.

In the example below, I started 10 nginx containers;

All these containers use the same image, so the "Virtual size" (183MB in the example) is used only once, irregardless of how many containers are started from the same image - I can start 1 container or a thousand; no extra disk space is used. The "Size" (2B in the example) is unique per container though, so the total space used on disk is:

183MB + 10 * 2B

Be aware that the size shown does not include all disk space used for a container. Things that are not included currently are;

• disk space used for log-files (if you use the json-file logging driver) - which can be quite a bit if your container generates a lot of logs, and log-rotation (max-file / max-size logging options) is not configured
• volumes used by the container
• disk space used for the container's configuration files (hostconfig.json, config.v2.json, hosts, hostname, resolv.conf) -
  although these files are small
• memory written to disk (if swapping is enabled)
• checkpoints (if you're using the experimental checkpoint/restore feature)