In Nodegrid 6.0 or greater, you can customize the docker data-root from the Web UI.  You can specify which disk partition to move the docker data-root.  Any mounted and formatted disk partition can be used.  The location will be created as /docker. If /docker already exists, then Nodegrid will not allow overwrite.

To change the docker data-root, navigate to System-->Services, then scroll to the "Enable Virtualization Services" section and ensure docker is enabled and then choose the location from the "Docker Directory Location" drop-down and save.