Here is my docker info
docker info
Containers: 7
Images: 3669
Storage Driver: devicemapper
Pool Name: docker-202:2-1548441-pool
Pool Blocksize: 65.54 kB
Backing Filesystem: extfs
Data file: /dev/loop0
Metadata file: /dev/loop1
Data Space Used: 59.74 GB
Data Space Total: 107.4 GB
Data Space Available: 12.53 GB
Metadata Space Used: 200 MB
Metadata Space Total: 2.147 GB
Metadata Space Available: 1.947 GB
Udev Sync Supported: true
Deferred Removal Enabled: false
Data loop file: /var/lib/docker/devicemapper/devicemapper/data
Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata
Library Version: 1.02.93-RHEL7 (2015-01-28)
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 3.10.0-229.14.1.el7.x86_64
Operating System: CentOS Linux 7 (Core)
CPUs: 8
Total Memory: 15.26 GiB
Name: DCLD1LXDOCKERDIST
ID: Q7PP:IMZH:PPZ4:3TRY:C3EV:5QLS:SJV3:V2YZ:EOEM:64B2:CCIL:QVK7
However devicemapper/data keeps all data without releasing the space, I tried restart docker, restart the VM, and this is reproduciable, so far it is happening on all our build servers and docker-registry server using Centos 7
ll -h /var/lib/docker/devicemapper/devicemapper/data
-rw------- 1 root root 100G Dec 9 08:07 /var/lib/docker/devicemapper/devicemapper/data