That's a storage volume (partition, raid volume, zfs pool, etc), not a filesystem. A filesystem is the abstraction layer on top of the storage volume translatin

That's a storage volume (partition, raid volume, zfs pool, etc), not a filesystem. A filesystem is the abstraction layer on top of the storage volume translating the user-assigned data identifiers (aka file names) to byte ranges. Talking specifically about databases: they often implement their own data organization. Oracle and Sybase famously performed better when working on raw partitions than with files.