本地存放docker镜像及容器元数据的位置

[root@rhels7-docker ~]# cat /var/lib/docker/image/devicemapper/repositories.json
{"Repositories":{"centos":{"centos:hadoop":"sha256:31deb9bb749d93473fdd7f01e0a2a5261d0540f75287cf42c9ae8da1b1a2b61a"},"daocloud.io/library/centos":{"daocloud.io/library/centos:centos7":"sha256:ea08fb8c4ba5494c7a77ba4381ba6fb8c871abd655c38c029a58ade8f5bb56fe"}}}

[root@rhels7-docker ~]# cat /var/lib/docker/image/devicemapper/repositories.json | python -mjson.tool
{
    "Repositories": {
        "centos": {
            "centos:hadoop": "sha256:31deb9bb749d93473fdd7f01e0a2a5261d0540f75287cf42c9ae8da1b1a2b61a"
        },
        "daocloud.io/library/centos": {
            "daocloud.io/library/centos:centos7": "sha256:ea08fb8c4ba5494c7a77ba4381ba6fb8c871abd655c38c029a58ade8f5bb56fe"
        }
    }
}

[root@rhels7-docker ~]# docker images
REPOSITORY                   TAG                 IMAGE ID            CREATED             SIZE
centos                       hadoop              31deb9bb749d        3 hours ago         1.434 GB
daocloud.io/library/centos   centos7             ea08fb8c4ba5        7 days ago          196.8 MB
[root@rhels7-docker ~]# du -h /var/lib/docker/devicemapper/devicemapper/*
1.6G    /var/lib/docker/devicemapper/devicemapper/data
4.5M    /var/lib/docker/devicemapper/devicemapper/metadata

/var/lib/docker/devicemapper/devicemapper/data
/var/lib/docker/devicemapper/devicemapper/metadata
这两个文件大小会随着image pull、rmi操做而相应的增大、减少。
可初步断定这两个文件就是docker pull ${image}以后，image的layers真正存储的地方。

从Docker镜像构建机制了解到
实际存放images和container的地方就是/var/lib/docker/devicemapper/devicemapper目录下的metadata和data两个文件。(元数据)

针对docker Version:      1.11.2

不一样docker版本可能存在差别