Discovering an external storage system

System initialization includes discovery process that identifies external storage systems and the Logical Units (LUs) that they export.

The discovery process systematically recognizes all visible ports on the SAN for devices that identify themselves as external storage systems. Each LU that the external storage system exports to the system is also identified. The LUs can contain new storage or a new path for previously discovered storage. The set of discovered LUs forms the managed disk (MDisk) view associated with external storage systems.

Requesting system discovery

The discovery process runs automatically when ports are added to or deleted from the SAN and when some error conditions occur.

To request the discovery process manually, use the Discover Storage function from the External Storage view in the management GUI. You can also use the detectmdisk command-line interface (CLI) command to request the discovery process manually. The request to perform discovery causes the clustered system to rescan the SAN. The rescan discovers any new MDisks that were added to the external storage systems and rebalances MDisk access across the available external storage-system ports.

The system discovery process completes asynchronously and might take a few minutes. When using the management GUI to perform system discovery, the GUI checks whether the discovery process is complete. When using the CLI to perform system discovery, use the lsdiscoverystatus command to check whether the discovery process is still in progress.

Discover new external storage system LUs

You can add newly exported external storage-system LUs to the system by using the system management GUI or the CLI.

When LUs are exported by creating LUN mappings on an external storage system, the system managed disk (MDisk) view is not always automatically updated. To update the view, you must request the system discovery process that is performed.

Note: If the data on the associated external storage-system LU needs to be preserved, then follow the Importing an external storage system procedure.

If newly added external storage systems do not appear in the MDisks display, ensure to cable the system correctly to the external storage systems.

Note: To achieve the best system performance, follow the guidelines for adding MDisks to pools as described in Pool configuration guidelines.

Discover external storage-system quorum-disks

During quorum disk discovery, the system assesses each external storage-system LU to determine its potential use as a quorum disk. From the set of eligible LUs, the system nominates three quorum candidate disks.

The MDisk associated with an external storage-system LU must meet the following criteria to be considered as a candidate for a quorum disk:
  • It must be in managed mode.
  • It must be visible to all nodes in the system.
  • It must be presented by an external storage system that is approved for quorum disks.
  • It must have sufficient free extents to hold the system state and the configuration metadata.
Note: Quorum disks cannot be placed on the iSCSI-attached external storage systems.
Quorum disk candidates are not found after the discovery because of one of the following situations:
  • LU MDisks of the external storage system does not exist in managed space mode. An error is logged when this situation occurs.
  • LU MDisks of the external storage system exists in managed space mode, but they do not meet the eligibility criteria. An error is logged when this situation occurs.