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.