The client (you) must talk to both the MDS and OSS servers in order to use the Lustre system.

• File I/O goes directly to one or more of the OSSs.
• The MDS is contacted when opening files, listing directories, etc.

But these behind-the-scenes interactions are invisible to you. On the client machine, the front end to the Lustre file system is nothing more than a Logical Object Volume (LOV) that simply appears like any other large volume that would be mounted on a node.