Off the top of my head, any one of these sounds like it might meet your requirements:
The GlusterFS I usually use is set up so that each file in the special "DATA" folder is stored twice somewhere on a 3-server cluster, each one running Red Hat, so if any one entire server is disconnected or unavailable, the data can still be retrieved from the other servers. So 10 machines, each with 400 GB reserved for Gluster, could act more or less like a single 10*400MB/2 = 2 TB drive.
As a normal user on any one machine, my "DATA" folder appears to act the same as the other normal local folders in Red Hat (permissions, sub-folders, etc.),
except that any changes appear to instantly show up in the corresponding "DATA" folder on any other machine in my cluster.
The MongoDB I usually use is a key:document datastore without any permissions, subfolders, etc.; but I hear that other people use the MongoDB GridFS to add those things.
Have you had a chance to look at
the Wikipedia article on distributed file systems
and the Wikipedia list of distributed file systems?
I'm glad you've already seen the Wikipedia article Comparison of distributed file systems; that sounds like exactly what you want.
I'm not familiar enough with the other file systems in those articles to tell whether they are better or worse for your application.