private void ensureRootExist() {
        if (! root.exists()) {
            if ( ! root.mkdir()) {
                throw new IllegalArgumentException("Failed creating root dir '" + root.getAbsolutePath() + "'.");
            }
        } else if (!root.isDirectory()) {
            throw new IllegalArgumentException("'" + root.getAbsolutePath() + "' is not a directory");
        }
    }
Global file directory, holding files for file distribution for all deployed applications.
configserver/src/main/java/com/yahoo/vespa/config/server/filedistribution/FileDirectory.java