Why Pushing Images to the Registry is Failing With "No Space Left on Device", in OpenShift Container Storage?

Issue

• After expanding the registry following the correct steps in OpenShift documentation, the available space in the file system shows enough room to push new images:

  oc rsh docker-registry-112233
  sh-4.2$ df -h /registry
  Filesystem                                           Size  Used Avail Use% Mounted on
  192.168.1.1:vol_XXXXXXXXXXX  300G  203G   98G  68% /registry
  

• However, when performing this task, the push commands fail with ENOSPC errors while running an mkdir. From the registry logs:

  time="2019-11-13T11:22:16.56372398Z" level=error msg="response completed with error" err.code=unknown err.detail="filesystem: mkdir /registry/docker/registry/v2/repositories/image-ts/image/_uploads/0ae86c9c-6653-49b1-a66a-406712789ef8: no space left on device" 
  

• Why is this occurring?