How to install docker's btrfs volume plugin? - docker

Question

When run command:
docker run -it -v some_volume:/abc/xyz --volume-driver=btrfs a_docker_image /bin/bash
terminal shows:
docker: Error response from daemon: create some_volume: Error looking up volume plugin btrfs: plugin not found.
====================
But if create volume first:
docker volume create --opt type=btrfs --name some_volume
It will create volume successfully. Now if I try to run container and create a new volume:
docker run -it -v some_volume:/abc/xyz --volume-driver=btrfs a_docker_image /bin/bash
It shows (of course it makes sense, since the same name volume has been already created):
docker: Error response from daemon: create some_volume: conflict: volume name must be unique.
And if I try to run container with the existing volume:
docker run -it -v some_volume:/abc/xyz a_docker_image /bin/bash
It returns:
docker: Error response from daemon: missing device in volume options.
====================
Could anyone help tell me how to install the volume plugin btrfs for docker? I haven't found any useful information regarding that except some introduction about plugin (but not how to install). Thanks in advance.
As suggested by #forevergenin in comments, here is my docker environment:
docker version
Client:
Version: 1.11.0
API version: 1.23
Go version: go1.5.4
Git commit: 4dc5990
Built: Wed Apr 13 18:13:28 2016
OS/Arch: darwin/amd64
Server:
Version: 1.11.0
API version: 1.23
Go version: go1.5.4
Git commit: 4dc5990
Built: Wed Apr 13 19:36:04 2016
OS/Arch: linux/amd64
docker info
Containers: 0
Running: 0
Paused: 0
Stopped: 0
Images: 39
Server Version: 1.11.0
Storage Driver: aufs
Root Dir: /mnt/sda1/var/lib/docker/aufs
Backing Filesystem: extfs
Dirs: 121
Dirperm1 Supported: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
Volume: local
Network: null host bridge
Kernel Version: 4.1.19-boot2docker
Operating System: Boot2Docker 1.11.0 (TCL 7.0); HEAD : 32ee7e9 - Wed Apr 13 20:06:49 UTC 2016
OSType: linux
Architecture: x86_64
CPUs: 1
Total Memory: 996.1 MiB
Name: default
ID: 74TB:OVH5:S3GD:UQUG:ILWG:5NVH:2MSH:5H7R:A5H4:GSLV:2Q6D:ZIR6
Docker Root Dir: /mnt/sda1/var/lib/docker
Debug mode (client): false
Debug mode (server): true
File Descriptors: 15
Goroutines: 32
System Time: 2016-08-15T13:57:03.866016657Z
EventsListeners: 0
Username: thyrlian
Registry: https://index.docker.io/v1/
Labels:
provider=virtualbox

Answer 1

I am new to btrfs with docker, but here is my understanding:
Using btrfs as a storage driver means that docker will use btrfs internally for the images and containers (that is explained here). Specifically, look at the installation details here: they make you create a btrfs partition and mount /var/lib/docker on it. When you restart your docker daemon after that, docker info should tell you "Storage Driver: btrfs".
Using the btrfs driver, the image's base is saved int /var/lib/docker/btrfs/subvolumes, and then they do snapshots (but I am not sure where they save them exactly). But that is done automatically without you specifying the driver (I would guess that specifying the driver is useful when you have multiple drivers that can run on a given filesystem. But the btrfs driver seems to be the default when /var/lib/docker is formatted in btrfs.
Regarding volumes, I believe that they are not saved as btrfs subvolumes. They seem to be simple folders in /var/lib/docker/volumes/. Again, I can imagine this as being the normal behavior of docker: images and containers are layered, but volumes are simple directories.
At least, that is the behavior I observe:
If I pull an image or create a container, I get btrfs subvolumes created.
I could create a volume by simply using docker volume create testvol1 and mount it in a container. But then it is not a btrfs subvolume.
If you want to have your volumes in btrfs subvolumes, then I believe that you might need to create the subvolumes manually and mount the volumes in them directly.