Unused docker image disappear occasionally

Hi All,

My docker images (mostly for unused) disappeared for unknown reasons, I already moved my docker storage location to my workspace which is 8T, and the workspace is not full. My configuration of docker is as below:

 Context:    default
 Debug Mode: false
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Build with BuildKit (Docker Inc., v0.5.1-docker)
  scan: Docker Scan (Docker Inc., v0.8.0)

 Containers: 3
  Running: 3
  Paused: 0
  Stopped: 0
 Images: 2
 Server Version: 20.10.7
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: d71fcd7d8303cbf684402823e425e9dd2e99285d
 runc version: b9ee9c6314599f1b4a7f497e1f1f856fe433d3b7
 init version: de40ad0
 Security Options:
   Profile: default
 Kernel Version: 4.15.0-142-generic
 Operating System: Ubuntu 16.04.7 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 8
 Total Memory: 31.26GiB
 Name: shaochun-gv
 Docker Root Dir: /local/mnt/workspace2/docker-images
 Debug Mode: false

And my workspace:

/dev/sdb1                                             7.3T  5.4T  1.6T  78% /local/mnt/workspace2
overlay                                               7.3T  5.4T  1.6T  78% /local/mnt/workspace2/docker-images/overlay2/0a083dccc4d87253ab39cd7ff6a1048bf0781d7b3d573116943a485bc47d3795/merged
overlay                                               7.3T  5.4T  1.6T  78% /local/mnt/workspace2/docker-images/overlay2/1b10884fc4a7801b1cdcc90187027271d6f8f3f66ae52f22883fbdd602341002/merged
overlay                                               7.3T  5.4T  1.6T  78% /local/mnt/workspace2/docker-images/overlay2/e78c7adf770e886c5b10917af31a06f47b4fdac73872933f9e8f6fb6dd56a333/merged

Hi, does anybody have similar issue?

Docker will not remove images automatically. If you see disappearing images, you must have another service that periodically removes unused images to make more space.