Discovering logical units

System initialization includes a process that is called discovery.

The discovery process systematically recognizes all visible ports on the SAN for devices that identify themselves as storage systems and the number of logical units (LUs) that they export. The LUs can contain new storage or a new path for previously discovered storage. The set of LUs forms the managed disk (MDisk) view.

The discovery process runs when ports are added to or deleted from the SAN and when certain error conditions occur. You can also manually run the discovery process by using the detectmdisk command-line interface (CLI) command or the Discover MDisks function from the management GUI. The detectmdisk command and the Discover MDisks function have the clustered system rescan the Fibre Channel network. The rescan discovers any new MDisks that were added to the system and rebalances MDisk access across the available storage-system device ports.
Note: Some storage systems do not automatically export LUs to the system.

Guidelines for exporting LUs

Ensure that you are familiar with the following guidelines for exporting LUs to the system:

  • When you define the system as a host object to the storage systems, you must include all ports on all nodes and candidate nodes.
  • When you first create an LU, you must wait until it is initialized before you export it to the system.
    Attention: Failure to wait for the LUs to initialize can result in excessive discovery times and an unstable view of the SAN.
  • Do not present new LUs to the system until the array initialization format is complete. If you add a LUN to a storage pool before the array initialization format is complete, the storage pool goes offline. While the storage pool is offline, you cannot access the volumes that are in the storage pool.
  • When you export an LU to the system, the LU must be accessible through all ports on the external storage system that are visible to the system.
    Important: The LU must be identified by the same logical unit number (LUN) on all ports.