Docker : Use External Storage2021/08/30

	When containers are removed, data in them are also lost, so it's necessary to use external filesystem in containers as persistent storages if you need.
[1]	It's possible to mount a directory on Docker Host into containers.

# create a directory for containers data

root@dlp:~#

mkdir -p /var/lib/docker/disk01

root@dlp:~#

echo "persistent storage" >> /var/lib/docker/disk01/testfile.txt

# run a container with mounting the directory above on [/mnt]

root@dlp:~#

docker run -it -v /var/lib/docker/disk01:/mnt debian /bin/bash

root@ed98ff6b35ef:/#

df -hT

Filesystem                  Type     Size  Used Avail Use% Mounted on
overlay                     overlay   77G  1.9G   72G   3% /
tmpfs                       tmpfs     64M     0   64M   0% /dev
shm                         tmpfs     64M     0   64M   0% /dev/shm
/dev/mapper/debian--vg-root ext4      77G  1.9G   72G   3% /mnt
tmpfs                       tmpfs    7.9G     0  7.9G   0% /proc/acpi
tmpfs                       tmpfs    7.9G     0  7.9G   0% /sys/firmware

root@ed98ff6b35ef:/#

cat /mnt/testfile.txt

persistent storage

[2]	It's also possible to configure external storage by Docker Data Volume command.

# create [volume01] volume

root@dlp:~#

docker volume create volume01

volume01

# display volume list

root@dlp:~#

docker volume ls

DRIVER    VOLUME NAME
local     volume01

# display details of [volume01]

root@dlp:~#

docker volume inspect volume01

[
    {
        "CreatedAt": "2021-08-29T19:14:57-05:00",
        "Driver": "local",
        "Labels": {},
        "Mountpoint": "/var/lib/docker/volumes/volume01/_data",
        "Name": "volume01",
        "Options": {},
        "Scope": "local"
    }
]

# run a container with mounting [volume01] to [/mnt] on container

root@dlp:~#

docker run -it -v volume01:/mnt debian

root@1411fa1337eb:/#

df -hT /mnt

Filesystem                  Type  Size  Used Avail Use% Mounted on
/dev/mapper/debian--vg-root ext4   77G  1.9G   72G   3% /mnt

root@1411fa1337eb:/#

echo "Docker Volume test" > /mnt/testfile.txt

root@1411fa1337eb:/#

exit

root@dlp:~#

cat /var/lib/docker/volumes/volume01/_data/testfile.txt

Docker Volume test

# possible to mount from other containers

root@dlp:~#

docker run -v volume01:/var/volume01 debian cat /var/volume01/testfile.txt

Docker Volume test

# to remove volumes, do like follows

root@dlp:~#

docker volume rm volume01

Error response from daemon: remove volume01: volume is in use - [4cbf4eeb2ef97f916b3c3a1ebf57009c6a82c484f91c9ba74edf87a26e725841, d11c0de4b68f62a45295db78a61d69d8933344583c2a00dc0a2a3a23b698efaa]

# if some containers are using the volume you'd like to remove like above,
# it needs to remove target containers before removing a volume

root@dlp:~#

docker rm 4cbf4eeb2ef97f916b3c3a1ebf57009c6a82c484f91c9ba74edf87a26e725841

root@dlp:~#

docker rm d11c0de4b68f62a45295db78a61d69d8933344583c2a00dc0a2a3a23b698efaa

root@dlp:~#

docker volume rm volume01

volume01

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