Another way to control the number of paths between hosts and the SAN Volume Controller  is to use  port mask . The port mask is an optional parameter of the  mkhost  and  chhost commands. 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. It then determines whether access  is allowed (port mask bit for given port is set) or denied (port mask bit is cleared). If access  is denied, the node responds to SCSI commands as though the HBA WWPN is unknown.  The port mask is 64 bits. Valid mask values range from all  0 s (no ports enabled) to all  1 s  (all ports enabled). For example, a mask of  0011  enables port 1 and port 2. The default  value is all  1 s. If the host has more than one HBA port per fabric, zone each host port with a separate  group of SAN Volume Controller ports.  To obtain the best overall performance of the subsystem and to prevent overloading, the  load of each SAN Volume Controller port should be equal. Assuming similar load  generated by each host, you can achieve this balance by zoning approximately the same  number of host ports to each SAN Volume Controller port. Figure 3-12 on page 63 shows an example of a balanced zoning configuration that was  created by completing the following steps: For consistency, use the same port number on each I/O Group node. The example on  Figure 3-12 on page 63 assigns ports 1 and 4 to one port set, and ports 2 and 3 to the  second set.  Because the I/O Group nodes have four FC ports each, two port sets are created. In general, for I/O Group nodes with more than four ports, divide the hosts into as many  groups as you created sets in step 1. The host connections in the example in Figure 3-12 on page 63 are defined in the  following manner:  Tip:  Create an alias for the I/O Group port set. This step makes it easier to correctly zone  hosts to the correct set of I/O Group ports. Additionally, it also makes host group  membership visible in the FC switch configuration. The use of this schema provides four paths to one I/O Group for each host, and helps to  maintain an equal distribution of host connections on SAN Volume Controller ports. Tip:  To maximize performance from the host point of view, distribute volumes that are  mapped to each host between both I/O Group nodes. 62  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1 GLYPH<SM590000> Balanced host load across HBA ports GLYPH<SM590000> Balanced host load across SAN Volume Controller ports 1. Divide ports on the I/O Group into two disjointed sets, such that each set contains two  ports from each I/O Group node, each connected to a different fabric. 2. Divide hosts attached to the I/O Group into two equally numerous groups. 3. Map each host group to exactly one port set. 4. Zone all hosts from each group to the corresponding set of I/O Group node ports.  – Hosts in group one are always zoned to ports 1 and 4 on both nodes. – Hosts in group two are always zoned to ports 2 and 3 on both nodes of the I/O Group.