If you no longer want a computer to act as a metadata controller for SAN volumes, you can demote the controller to a SAN client.
In the Xsan pane of the Server app, select the Controllers tab.
Select the controller to remove.
Click “Remove [controller name],” then click OK to confirm.
On the demoted client, install the client configuration profile.
You can’t remove the metadata controller that is acting as the Open Directory Master, without making another metadata controller the Open Directory Master first. See Make a standby controller the Open Directory Master.