mdconfig(8) on FreeBSD
The text ff20e29dfb27, as FreeBSD 11.0-RELEASE shipped it.
create and control memory disks
Flags it lists
-
-S -
-a -
-d -
-f -
-l -
-n -
-o -
-r -
-s -
-t -
-u -
-x -
-y