A host system is a computer that is connected to the SAN Volume Controller through either a fibre-channel interface or an IP network.
A host object is a logical object in the SAN Volume Controller that represents a list of worldwide port names (WWPNs) and a list of iSCSI names that identify the interfaces that the host system uses to communicate with the SAN Volume Controller. iSCSI names can be either iSCSI qualified names (IQNs) or extended unique identifiers (EUIs).
A typical configuration has one host object for each host system that is attached to the SAN Volume Controller. If a cluster of hosts accesses the same storage, you can add HBA ports from several hosts to one host object to make a simpler configuration. A host object can have both WWPNs and iSCSI names.
The cluster does not automatically present virtual disks (VDisks) to the host system. You must map each VDisk to a particular host object to enable the VDisk to be accessed through the WWPNs or iSCSI names that are associated with the host object.
When you create a new host object, the configuration interfaces provide a list of unconfigured WWPNs. These represent the WWPNs that the cluster has detected. Candidate iSCSI names are not available and must be entered manually.
The cluster can detect only WWPNs that have connected to the cluster through the fibre-channel network. Some fibre-channel HBA device drivers do not let the ports remain logged in if no disks are detected on the fabric. This can prevent some WWPNs from appearing in the list of candidate WWPNs. The configuration interface provides a method to manually type the port names.
A WWPN or iSCSI name can be added to only one host object.
You can use the port-mask property of the host object to control the fibre-channel ports on each SAN Volume Controller node that a host can access. The port mask applies to logins from the WWPNs that are associated with the host object. The port-mask configuration has no effect on iSCSI connections.
For each login between a host fibre-channel port and node fibre-channel port, the node examines the port mask for the associated host object and determines if access is allowed or denied. If access is denied, the node responds to SCSI commands as if the HBA WWPN is unknown.
The port mask is four binary bits. Valid mask values range from 0000 (no ports enabled) to 1111 (all ports enabled). For example, a mask of 0011 enables port 1 and port 2. The default value is 1111.
When you create a VDisk-to-host mapping to a fibre-channel attached host, the host ports that are associated with the host object can view the LUN that represents the VDisk on up to eight fibre-channel ports. Nodes follow the American National Standards Institute (ANSI) Fibre Channel (FC) standards for SCSI LUs that are accessed through multiple node ports. All nodes within a single I/O group present a consistent set of SCSI LUs across all ports on those nodes.
Similarly, all nodes within a single I/O group present a consistent set of SCSI LUs across all iSCSI ports on those nodes.
The number of nodes that can see each WWPN or iSCSI name is reported on a per-node basis and is known as the node login count. If the count is less than expected for the current configuration, you might have a connectivity problem.