Why do you have 500G allocated to docker.img?
20G should be more than enough. You must have one or more applications misconfigured and writing into docker.img instead of to mapped host storage.
I am running 17 dockers and they are using less than half of 20G docker.img. But I see you are already using much more than 20G even after restarting.
Making docker.img larger won't fix anything, it will just make it take longer to fill.
The usual reason for filling docker.img is specifying paths in your applications that don't exactly match the container path in your mappings. Common mistakes are specifying different upper/lower case (linux is case-sensitive) than in your container mappings or specifying a relative path (a path not beginning in /).
Also, your system and domains shares are on the array instead of all on cache where they belong, like your appdata.
appdata, domains, system should be all on cache and set to stay on cache. If you have these on the array, your dockers / VMs will have their performance impacted by slower parity writes, and they will keep array disks spinning since these files will always be open.
Do you actually have any VMs?
Which dockers do you use?