I’d be curious to see du -i to see what’s going on with inodes. Alternatively I did have an issue long time ago with docker containers, sparse files and dirty disk. Force-running fsck resolved my issues in the past.

My opinion is that of the two Postres is more “adult”. So if you want to"just wing it" MariaDB would work, but if you’re serious Postgres is a better choice. However Postgres also requires better understanding of you setup etc. So it’s a ROI game - what’s more important to your project, how complex your DB is, what are the requirements for availability, transaction security etc. There is no “better” or “worse” there’s “feasible” and “prohibitive” 😉