When a Kudu server starts up, it checks the dirs listed in --fs_data_dirs to see if it needs to create a new fs layout. If a layout already exists in these directories, it checks the integrity of the metadata in these directories (e.g. ensuring the disks have a cohesive view of the data dir configuration) and proceeds.
Right now, the only way to add a directory to a server and ensure the integrity of the fs layout is to wipe the entire server and add to --fs_data_dirs. It would be nice if we had a tool to instead update the appropriate files needed to pass the integrity check when adding a data dir.