attaching the cables for a LUN-mapped channel pair, make sure that the first channel is connected to the upper port and the second channel is connected to the lower port of the second channel.
For example, to provide redundancy, map half of the LUNs across Channel 0 (PID
40) and Channel 4 (PID 42), and then map the other half of your LUNs across Channel 1 (SID 41) and Channel 5 (SID 43).
■Point-to-point mode allows a maximum of 128 LUNs per array. In a redundant configuration, 32 LUNs are dual-mapped across two channels on the primary controller, and another 32 LUNs are dual-mapped across the secondary controller, for a total of 64 distinct LUNs.
■To use more than 64 LUNs, you must change to loop only mode, add host IDs to one or more channels, and add 32 LUNs for each additional host ID.
Note – When in loop mode and connected to a fabric switch, each host ID is displayed as a loop device on the switch so that, if all 16 IDs are active on a given channel, the array looks like a loop with 16 nodes attached to a single switch FL port.
In public loop mode, the array can have a maximum of 1024 LUNs, where 512 LUNs are dual-mapped across two channels, primary and secondary controller respectively.
5.1.2A Sample SAN Point-to-Point Configuration
A point-to-point configuration has the following characteristics:
■In SAN configurations, the switches communicate with the SANnet II 200 Fibre Channel array host ports using a fabric point-to-point (F_port) mode.
■When you use fabric point-to-point (F_port) connections between a FC, SATA, or SATA SE array and fabric switches, the maximum number of LUNs is limited to 128 LUNs for a nonredundant configuration and 64 LUNs for a redundant configuration.
■Fibre Channel standards allow only one ID per port when operating point-to-point protocols, resulting in a maximum of four IDs with a maximum of 32 LUNs for each ID, and a combined maximum of 128 LUNs.
■The working maximum number of LUNs is actually 64 LUNs in a configuration where you configure each LUN on two different channels for redundancy and to avoid a single point of failure.
In a dual-controller array, one controller automatically takes over all operation of a second failed controller in all circumstances. However, when an I/O controller module needs to be replaced and a cable to an I/O port is removed, the I/O path is broken unless multipathing software has established a separate path from the host to the operational controller. Supporting hot-swap servicing of a failed controller requires the use of multipathing software, such as SANpath software, on the connected servers.
