Whats the different between /var/lib/containerd/io.containerd.snapshotter.v1.overlayfs and /var/lib/docker/rootfs/overlayfs

[lystormenvoy]

I have a nginx container. Then I found some files exist in both /var/lib/containerd/io.containerd.snapshotter.v1.overlayfs and /var/lib/docker/rootfs/overlayfs at the same time

[root@VM-48-10-tencentos 11]# md5sum ec7c5c32782b9c75c58f241c96b97111 
847f645f9ce2049c18a910448d92ee15  ec7c5c32782b9c75c58f241c96b97111
[root@VM-48-10-tencentos 11]# pwd
/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/145/fs/usr/local/openresty/nginx/proxy_cache/1/11

[root@VM-48-10-tencentos 11]# md5sum ec7c5c32782b9c75c58f241c96b97111 
847f645f9ce2049c18a910448d92ee15  ec7c5c32782b9c75c58f241c96b97111
[root@VM-48-10-tencentos 11]# pwd
/var/lib/docker/rootfs/overlayfs/c4b1ddfe9c10bc8d37870fcc2a98ac7296cc4ffce61ea0eee33bae61c19b4e26/usr/local/openresty/nginx/proxy_cache/1/11

The file in proxy_cache was generated after I created the container.
Why is it stored in different paths and taking up double the disk space?

My version:

[root@VM-48-10-tencentos 11]# containerd --version
containerd github.com/containerd/containerd/v2 v2.2.0 1c4457e00facac03ce1d75f7b6777a7a851e5c41
[root@VM-48-10-tencentos 11]# docker version
Client:
 Version:           29.1.3
 API version:       1.52
 Go version:        go1.25.5
 Git commit:        f52814d
 Built:             Fri Dec 12 14:48:47 2025
 OS/Arch:           linux/amd64
 Context:           default
                                                                                                                                                       
Server: Docker Engine - Community
 Engine:
  Version:          29.1.3
  API version:      1.52 (minimum version 1.44)
  Go version:       go1.25.5
  Git commit:       fbf3ed2
  Built:            Fri Dec 12 14:51:14 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v2.2.0
  GitCommit:        1c4457e00facac03ce1d75f7b6777a7a851e5c41
 runc:
  Version:          1.3.4
  GitCommit:        v1.3.4-0-gd6d73eb
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

[lystormenvoy]

I have found that they are the same file