containers: mountpoint section

pct.adoc

@@ -372,6 +372,32 @@ Files
 Configuration file for the container '<CTID>'.
 
 
+Container Mountpoints
+---------------------
+
+Beside the root directory the container can also have additional mountpoints.
+Currently there are basically three types of mountpoints: storage backed
+mountpoints, bind mounts and device mounts.
+
+Storage backed mountpoints are managed by the {pve} storage subsystem and come
+in three different flavors:
+
+- Image based: These are raw images containing a single ext4 formatted file
+  system.
+- ZFS Subvolumes: These are technically bind mounts, but with managed storage,
+  and thus allow resizing and snapshotting.
+- Directories: passing `size=0` triggers a special case where instead of a raw
+  image a directory is created.
+
+Bind mounts are considered to not be managed by the storage subsystem, so you
+cannot make snapshots or deal with quotas from inside the container, and with
+unprivileged containers you might run into permission problems caused by the
+user mapping, and cannot use ACLs from inside an unprivileged container.
+
+Similarly device mounts are not managed by the storage, but for these the
+`quota` and `acl` options will be honored.
+
+
 Container Advantages
 --------------------