When a virtual machine issues an I/O request to a storage device managed by the NMP, the following process takes place.

  1. The NMP calls the PSP assigned to this storage device.
  2. The PSP selects an appropriate physical path on which to issue the I/O.
  3. The NMP issues the I/O request on the path selected by the PSP.
  4. If the I/O operation is successful, the NMP reports its completion.
  5. If the I/O operation reports an error, the NMP calls the appropriate SATP.
  6. The SATP interprets the I/O command errors and, when appropriate, activates the inactive paths.
  7. The PSP is called to select a new path on which to issue the I/O.