Docker /vfs folder size - docker

Question

I have a problem with my docker.
I've downloaded an image, and docker shows its size about 600Mb.
But on the disk, in the /usr/lib/docker/ its using like almost 6Gb.
Here is my folder before image pull:
/..
27.9 MiB [##########] /tmp
236.0 KiB [ ] /image
60.0 KiB [ ] /network
8.0 KiB [ ] /vfs
e 4.0 KiB [ ] /volumes
e 4.0 KiB [ ] /trust
e 4.0 KiB [ ] /containers
And here is after image pull:
/..
5.8 GiB [##########] /vfs
27.9 MiB [ ] /tmp
2.2 MiB [ ] /image
60.0 KiB [ ] /network
e 4.0 KiB [ ] /volumes
e 4.0 KiB [ ] /trust
e 4.0 KiB [ ] /containers
Image itself:
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/bitnami/mariadb latest f5dbed792113 8 days ago 598.1 MB
And its history:
IMAGE CREATED CREATED BY SIZE COMMENT
f5dbed792113 8 days ago /bin/sh -c #(nop) CMD ["/run.sh"] 0 B
<missing> 8 days ago /bin/sh -c #(nop) ENTRYPOINT &{["/app-entrypo 0 B
<missing> 8 days ago /bin/sh -c #(nop) EXPOSE 3306/tcp 0 B
<missing> 8 days ago /bin/sh -c #(nop) VOLUME [/bitnami/mariadb] 0 B
<missing> 8 days ago /bin/sh -c #(nop) ENV ALLOW_EMPTY_PASSWORD=no 0 B
<missing> 8 days ago /bin/sh -c #(nop) COPY dir:c5bea93fb9ce36dc47 3.758 kB
<missing> 8 days ago /bin/sh -c bitnami-pkg unpack mariadb-10.1.23 482.1 MB
<missing> 8 days ago /bin/sh -c install_packages libaio1 libc6 lib 12.29 MB
<missing> 8 days ago /bin/sh -c #(nop) LABEL maintainer=Bitnami <c 0 B
<missing> 3 weeks ago /bin/sh -c #(nop) ENTRYPOINT &{["/entrypoint. 0 B
<missing> 3 weeks ago /bin/sh -c #(nop) COPY dir:21a422cab8e9367936 10.17 kB
<missing> 3 weeks ago /bin/sh -c #(nop) ENV BITNAMI_IMAGE_VERSION=j 0 B
<missing> 3 weeks ago /bin/sh -c #(nop) ENV PATH=/opt/bitnami/nami/ 0 B
<missing> 3 weeks ago /bin/sh -c cd /tmp && gpg --keyserver hkp:/ 1.423 MB
<missing> 3 weeks ago /bin/sh -c #(nop) ENV GOSU_VERSION=1.10 GOSU_ 0 B
<missing> 3 weeks ago /bin/sh -c cd /tmp && gpg --keyserver hkp:/ 40.76 kB
<missing> 3 weeks ago /bin/sh -c #(nop) ENV TINI_VERSION=v0.13.2 0 B
<missing> 3 weeks ago /bin/sh -c cd /tmp && curl -sSLO https://na 16.77 MB
<missing> 3 weeks ago /bin/sh -c #(nop) ENV NAMI_VERSION=0.0.6-0 0 B
<missing> 3 weeks ago /bin/sh -c install_packages curl ca-certifica 34.3 MB
<missing> 3 weeks ago /bin/sh -c #(nop) LABEL maintainer=Bitnami <c 0 B
<missing> 3 weeks ago 51.14 MB from Bitnami with love
I'm new to the Docker, so is this normal?
I'm find that quite insane. Whole linux VM might be smaller, than this mariadb image.
How i can resolve this?
My docker info:
Containers: 0
Running: 0
Paused: 0
Stopped: 0
Images: 1
Server Version: 1.10.3
Storage Driver: vfs
Execution Driver: native-0.2
Logging Driver: journald
Plugins:
Volume: local
Network: bridge null host
Kernel Version: 2.6.32-042stab120.20
Operating System: CentOS Linux 7 (Core)
OSType: linux
Architecture: x86_64
Number of Docker Hooks: 2
CPUs: 1
Total Memory: 512 MiB
WARNING: No oom kill disable support
WARNING: bridge-nf-call-ip6tables is disabled
Registries: docker.io (secure)

Answer 1

The problem is the vfs storage driver.
Quoting Storage Drivers in Docker: A Deep Dive
First, let’s get the one special graphdriver out of the way–vfs is the
“naive” implementation of the interface that does not use a union
filesystem or CoW techniques at all, but rather copies all the layers
in order into a static subdirectory and mounts the end result as the
container root filesystem. It is not meant for real (production) use
but is very valuable for simple validation and testing of other parts
of the Docker engine.
My advise is to upgrade to the latest CentOS 7.2 to obtain the latest kernel version they support and use overlay2:
https://docs.docker.com/engine/userguide/storagedriver/overlayfs-driver/

Answer 2

With VFS storage driver each RUN/COPY/ADD instruction in Dockerfile creates a full copy of image's filesystem during image build. So, if your Dockerfile file contains ten RUNs, it will create ten layers/copies.
The solution to this is to reduce the number of RUN/COPY/ADD instructions or to use other drivers (e.g. Overlay2) that copy only changed files..
Also the final number of layers can be reduced by using instructions below at the end of Dockerfile:
FROM scratch
COPY --from=0 / /
It causes that all layers created before the FROM scratch instruction can be forgotten and freed (with docker image prune). What COPY does, refer here, it basically copy all files from one stage to new one.
You can check this Dockerfile for usage example.