In the multipath state, the asymmetric logical unit access (ALUA) mode presents active/passive LUNs to the host and provides an access status switching interface to switch the LUNs' working controller.
SCSI (SPC) ALUA:
1. Defines the status model of target ports (front-end ports of storage arrays).
2. Describes the SCSI commands used for querying and managing port status.
The multipath software:
1. Uses SCSI commands to query target port status, obtain the path priority, and manage paths.
2. Employs control commands to access target ports in different states to select the optimal path.
3. Uses SCSI commands to set port status to control the path priority.
In short, ALUA is a SCSI port model and port management mode. It enables host multipath software to manage paths based on the mode.