Make sure to change the MP unit ID of an LDEV while the I/O load is low. If the MP unit ID is changed under high load, I/O delays might occur and impact the operations. Check the following precautions before changing the MP unit ID.
CAUTION:
- If the LDEV is used as a utility volume for IBM® XRC, you can change the MP unit assigned to the LDEV only when the XRC session is suspended and the number of side files of the target session is zero.
- Changes to the MP unit ID of an LDEV should be made during off-peak hours when the I/O load is as low as possible. Before and after changes are made, the cache write-pending rate (%) for all CLPRs should be lower than 50%. Do not change the MP unit ID when the I/O load is high, for example, during initial copy of ShadowImage for Mainframe, TrueCopy for Mainframe, or Universal Replicator for Mainframe.
- When you change the MP unit ID of an LDEV, check the load status of devices before and after the change. Do not change several LDEV MP unit IDs during a short period of time. As a guideline, you can change 10% or less of the total number or the full workload of LDEV MP unit IDs assigned to the same MP unit ID at the same time.
- After you change the MP unit for an LDEV, wait more than 30 minutes before you try to change the ID again for the same LDEV.