IBM TS2340 User Guide - Page 31

Path Failover recovery for systems connected to tape drives while CPF is an automatic failover support for the transfer of commands to move tape cartridges. Below are examples of different configurations that can be constructed. Multiple HBA and Multi-Port Devices Consider a multipath connection that consists of two Host Bus Adapters (HBA) connected through a fabric to a multi-port device. By having two connections from each device to the fabric, a configuration of four different physical paths can be set up. e.g. HBA A to port 1, HBA A to port 2, HBA B to port 1, and HBA B to port 2. One path is the primary path and the other three would be alternate paths. If the primary path should have a failure, the Automatic Failover would try switching to another configured path. Without path failover support, if a permanent path error occurs (because of an HBA or cable failure, for example), the application fails. However should that occur with this configuration there would still be two valid physical paths for the data to be transmitted on and the running application wouldn't be affected. Dual HBA Mulit-Port Drive (DPF) Fabric X Library (CPF) Drive X Drive Library Controller Drive X Virtual Tape Library (DPF and CPF) a2500255 Figure 3. Multiple HBA and multi-port devices Multiple HBA and Single Ports For another example, consider the same multipath connection that consists of two Host Adapters connected through a fabric to a single port device. This configuration would supply two physical paths to the same device, however, if the port or cable from the device fails the automatic failover would not work as that connection is severed and a permanent path error occurs. If however the failure was with one of the HBAs or their cables the automatic data path failover would select the other HBA and the information would continue through the alternate path. Chapter 2. Common Extended Features 13