 /**
   * Upgrade to any release after 0.22 (0.22 included) release e.g. 0.22 => 0.23
   * Upgrade procedure is as follows:
   * <ol>
   * <li>If <SD>/current/<bpid>/previous exists then delete it</li>
   * <li>Rename <SD>/current/<bpid>/current to
   * <SD>/current/bpid/current/previous.tmp</li>
   * <li>Create new <SD>current/<bpid>/current directory</li>
   * <ol>
   * <li>Hard links for block files are created from previous.tmp to current</li>
   * <li>Save new version file in current directory</li>
   * </ol>
   * <li>Rename previous.tmp to previous</li> </ol>
   * 
   * @param bpSd storage directory <SD>/current/<bpid>
   * @param nsInfo Namespace Info from the namenode
   * @throws IOException on error
   */
 /**
   * Upgrade to any release after 0.22 (0.22 included) release e.g. 0.22 => 0.23
   * Upgrade procedure is as follows:
   * <ol>
   * <li>If <SD>/current/<bpid>/previous exists then delete it</li>
   * <li>Rename <SD>/current/<bpid>/current to
   * <SD>/current/bpid/current/previous.tmp</li>
   * <li>Create new <SD>current/<bpid>/current directory</li>
   * <ol>
   * <li>Hard links for block files are created from previous.tmp to current</li>
   * <li>Save new version file in current directory</li>
   * </ol>
   * <li>Rename previous.tmp to previous</li> </ol>
   * 
   * @param bpSd storage directory <SD>/current/<bpid>
   * @param nsInfo Namespace Info from the namenode
   * @throws IOException on error
   */ | BlockPoolSliceStorage.java