Docker : Use External Storage2022/09/08

	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 ubuntu /bin/bash

root@3f90e49252cb:/#

df -hT

Filesystem                        Type     Size  Used Avail Use% Mounted on
overlay                           overlay   77G  8.9G   64G  13% /
tmpfs                             tmpfs     64M     0   64M   0% /dev
shm                               tmpfs     64M     0   64M   0% /dev/shm
/dev/mapper/ubuntu--vg-ubuntu--lv ext4      77G  8.9G   64G  13% /mnt
tmpfs                             tmpfs    7.9G     0  7.9G   0% /proc/acpi
tmpfs                             tmpfs    7.9G     0  7.9G   0% /proc/scsi
tmpfs                             tmpfs    7.9G     0  7.9G   0% /sys/firmware

root@3f90e49252cb:/#

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": "2022-09-07T07:49:47Z",
        "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 ubuntu

root@039c03a8e089:/#

df -hT /mnt

Filesystem                        Type  Size  Used Avail Use% Mounted on
/dev/mapper/ubuntu--vg-ubuntu--lv ext4   77G  8.9G   64G  13% /mnt

root@039c03a8e089:/#

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

root@039c03a8e089:/#

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 ubuntu /usr/bin/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 - [969eea8e7c9bc646f6a59f01072509c36324003008ef4d23665abcf411f912e8, 039c03a8e089a588d4115a2aacec369b4fcc731a626dfe32977043c96e395376]

# 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 969eea8e7c9bc646f6a59f01072509c36324003008ef4d23665abcf411f912e8

root@dlp:~#

docker rm 039c03a8e089a588d4115a2aacec369b4fcc731a626dfe32977043c96e395376

root@dlp:~#

docker volume rm volume01

volume01

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