IBM TS2340 User Guide - Page 56

AIX Device Driver (Atape) To enable or disable the support on a single logical device, use the smit menu to Change/Show Characteristics of a Tape Drive, select the logical device to change such as smc0, smc1, and so on, then select Yes or No for Enable Path Failover Support. The support can also be enabled or disabled using the chdev command, for example: chdev -l smc0 -aalt_pathing=yes chdev -l smc1 -aalt_pathing=yes chdev -l smc0 -aalt_pathing=no chdev -l smc1 -aalt_pathing=no Primary and Alternate Paths When the device driver configures a logical device with path failover support enabled, the first device configured always becomes the primary path. On SCSI attached devices, -P is appended to the location field. On Fibre attached devices, -PRI is appended to the location field of the device. When a second logical device is configured with path failover support enabled for the same physical device, it configures as an alternate path. On SCSI attached devices, -A is appended to the location field. On Fibre attached devices, -ALT is appended to the location field of the device. A third logical device is also configured as an alternate path with either -A or -ALT appended, and so on. The device driver supports up to 16 physical paths for a single device. The labeling of a logical device as either a primary or alternate path is for information only, in order to: 1. Be able to identify the actual number of physical devices configured on the system and a specific logical device associated with them. There is only one logical device labeled as the primary path for each physical device. However, there can be many (multiple) logical devices labeled as an alternate path for the same devices. 2. Provide information about which logical devices configured on the system have path failover support enabled. Querying Primary and Alternate Path Configurations You can display the primary and alternate path configuration for all devices with the lsdev command. There can be two or more logical devices configured for a single physical device, but the first device configured is labeled the primary device. All other logical devices configured after the first device are labeled as alternate devices. To see this, run the lsdev -Cc tape command and look at the location field in the data. Run the following command: lsdev -Cc tape | grep P For example, you can easily determine how many physical devices are configured with path failover support. Note: Display the primary and alternate path configuration for any device using tape diagnostic and utility functions, refer to Chapter 10, "IBM Tape Diagnostic Tool (ITDT)," on page 259 or "AIX System - Tape Utility Program (tapeutil)" on page 362. 38 IBM Tape Device Drivers Installation and User's Guide