I made a mistake with Docker and now it's filled up a ~100 gig ssd with invisible files. After investigation I believe the simplest solution is to wipe the drive and reinstall OMV. However it's managing a RAID6 and I have almost no experience with Linux.
I'm posting here because I'd like to make this as painless as possible (exfiltrating config files, preserving the RAID6 info, etc). The NAS is a home NAS and can be turned off for long periods with no major problems as it's only running UrBackup for one machine at the moment. Thanks for the help.