Images and videos for sure, if only %25 of the 30GB is events, you need 7.5M events. The biggest relay stores 3M events only.
It's a media cache issue.
Discussion
My cache folder is using 34G. My lmdb folder is using 4.3G (I prune it, it has gotten up to 12G or so). It could be either.
The local database doesn't just store events. There are lots of other records.