Yeah, until the mid '00s you would run your db directly to raw disk devices, both in order to optimize the use of larger contiguous disk regions (disk drives we

Yeah, until the mid '00s you would run your db directly to raw disk devices, both in order to optimize the use of larger contiguous disk regions (disk drives were slow in those days!) and, crucially, because if/when your server went down hard any pending OS-buffered writes would result in a corrupted database, lost data, and lengthy rebuilds from logs (generally after having to do a long fsck recovery just to get back into the OS). It wasn't until journaled filesystems became common and battle-tested that you saw databases living in the filesystem proper.