How to increase docker container disk size (devicemapper)

Inside the docker container check the available disk space and get the path to the partition:

root@server2:~# docker exec stefan df -h /var/lib/docker/devicemapper/mnt/bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc
Filesystem                                                                                        Size  Used Avail Use% Mounted on
/dev/mapper/docker-252:1-791489-bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc   20G  1.2G   19G   6% /var/lib/docker/devicemapper/mnt/bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc

Current allocated disk size for the container is 20GB and path is: /var/lib/docker/devicemapper/mnt/bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc

In the following commands we will increase the size to 50GB.

1.) Calculate the number of blocks in 50GB:

root@server2:~# echo $((50*1024*1024*1024/512))
104857600

2.) Write the dmtable:

root@server2:~# dmsetup table docker-252:1-791489-bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc

0 41943040 thin 253:0 218

root@server2:~# echo 0 104857600 thin 253:0 218 | sudo dmsetup load docker-252:1-791489-bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc

root@server2:~# sudo dmsetup resume docker-252:1-791489-bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc

root@server2:~# sudo dmsetup table docker-252:1-791489-bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc

0 104857600 thin 253:0 216

root@server2:~# xfs_growfs /var/lib/docker/devicemapper/mnt/bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc
meta-data=/dev/mapper/docker-252:1-791489-bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc isize=512    agcount=32, agsize=163840 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=1, rmapbt=0
         =                       reflink=1    bigtime=0 inobtcount=0
data     =                       bsize=4096   blocks=5242880, imaxpct=25
         =                       sunit=16     swidth=16 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=16 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 5242880 to 13107200

3.) Finally, lets check the size again:

root@server2:~# docker exec stefan df -h /var/lib/docker/devicemapper/mnt/bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc
Filesystem                                                                                        Size  Used Avail Use% Mounted on
/dev/mapper/docker-252:1-791489-bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc   50G  1.4G   49G   3% /var/lib/docker/devicemapper/mnt/bddbf234169773b6d6b52529ff32572add386085bc248a0ee807f70ce7c00adc