Before defining LU paths, you must classify server hosts by host groups. For more information, see Host groups.
After server hosts are classified into host groups, you associate the host groups with logical volumes. The following figure illustrates LU path configuration in a Fibre Channel environment. The figure shows host group hg-lnx associated with three logical volumes (00:00:00, 00:00:01, and 00:00:02). LU paths are defined between the two hosts in the hg-lnx group and the three logical volumes.
You can define paths between a single server host and multiple LUs. The figure shows that each of the two hosts in the host group hg-lnx can access the three LUs.
You can also define paths between multiple server hosts and a single LU. The figure shows that the LU identified by the LDKC:CU:LDEV number 00:00:00 is accessible from the two hosts that belong to the hg-lnx host group.
The figure also shows that the LUs associated with the hg-lnx host group are addressed by numbers 0000 to 0002. The address number of an LU is referred to as a LUN (logical unit number). When software manipulates LUs, the software uses LUNs to specify the LUs to be manipulated.
You can add, change, and delete LU paths when the system is in operation. For example, if new drives or server hosts are added to your storage system, you can add new LU paths. If an existing server host is to be replaced, you can delete the LU paths that correspond to the host before replacing the host. You do not need to restart the system when you add, change, or delete LU paths.
In a Fibre Channel environment, up to 2,048 LU paths can be defined for one host group, and up to 2,048 LU paths can be defined for one port.
The maximum number of host groups that can be created is 255 per Fibre Channel port. The maximum number of WWNs of host bus adapters that can be registered is 255 per host group, and 255 per Fibre Channel port.
If a hardware failure occurs, there is a chance that some LU paths are disabled, and some I/O operations are stopped. To avoid such a situation, you can define alternate LU paths; if one LU path fails, the alternate path takes over the host I/O.
You cannot set an LU path to a volume that is set as a namespace. (A namespace is a logical volume that is available from a host that supports NVMe-oF communication protocol.)