IBM TS2340 User Guide - Page 54
Persistent Naming Support, Changing the Logical Name After Initial Boot, Special File Name
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AIX Device Driver (Atape) Table 7. Special Files for Medium Changer Devices (continued) Special File Name Description Note: The smc*.null file is a pseudo device similar to the /dev/null AIX special file. The commands can be issued to this file without a real device attached to it, and the device driver returns a successful completion. This file can be used for application development or debugging problems. The file descriptor that results from opening the smc special file does not support the following operations: v Read v Write v Commands designed for a tape device Persistent Naming Support Persistent naming support is used to ensure that attached devices are always configured with the same logical name based on the SCSI ID, LUN ID, and host bus adapter (HBA), even when the system is rebooted. When the AIX operating system is booted, the HBA performs a device discovery and assigns a default logical name to each device found in a sequential order. For example, if there are three tape drives attached to a parallel SCSI adapter, each with a LUN ID of 0 and a target address of 0, 1, and 2 respectively, the HBA would initially configure them as Available with the following logical names: rmt0 rmt1 rmt2 target 0, lun 0 target 1, lun 0 target 2, lun 0 Available Available Available On the next reboot, for example, if the existing rmt1 target 1 device is powered off or not connected, the HBA would initially configure two devices as Available with the following logical names: rmt0 rmt1 target 0, lun 0 target 2, lun 0 Available Available If the previous rmt1 target 1 device is powered on after reboot and the cfgmgr command is run, the HBA configures the device as rmt2 instead of rmt1: rmt2 target 1, lun 0 Available This is one example, but there are other cases where the logical names of devices could change when the system is rebooted. For applications that need a consistent naming convention for all attached devices, this is accomplished with persistent naming support by defining a unique logical name (other than the AIX default names) that are associated with the specific SCSI ID, LUN ID, and HBA that the device is connected to. Changing the Logical Name After Initial Boot The logical name of a device can be changed after an initial boot and configured. This can be done using the SMIT menu or the chdev command from a script or command line. 36 IBM Tape Device Drivers Installation and User's Guide