If you run the CHECK LOB utility in Db2 12 or Db2 11 for z/OS, you will be happy to learn that performance has just gotten better. The IBM Db2 Development team has recently changed the code so that the CHECK LOB utility now uses more prefetch than before. This can result in a dramatic reduction in synchronous read I/O and a significant reduction in CPU and elapsed times.
Internal testing shows a reduction in CPU time of 47% and a reduction in elapsed time of 92%, due to the use of prefetch engines. Your results will undoubtedly vary, but performance should be significantly better than before.