As with any VFS that is configured on top of the PublishingFileRepository, a custom VFS must have a corresponding VFS at the same Nucleus location on the appropriate servers in each staging or production target where you intend to deploy the files.
In the FTPFileSystem example, there might be a single production target, which includes a single FTP server. You need to configure a VFS named /mycompany/FTPFileSystem on that FTP server.
For detailed information on configuring custom VFSs in deployment targets, see Configure Custom Target VFSs for Switch Deployments or Configure Custom VFSs for Online Deployments in the Setting Up Deployment chapter.
