Special files for tape devices

Each tape device has a set of special files that provides access to the same physical drive but to different types of functions. In addition to the tape special files, a special file is provided to tape devices that allow access to the medium changer as a separate device. See Table 1. The asterisk (*) represents a number that is assigned to a particular device (such as rmt0).

Table 1. Special files for tape devices
Special File Name Rewind on Close1 Retension on Open2 Bytes per Inch3 Trailer Label Unload on Close
/dev/rmt* Yes No N/A No No
/dev/rmt*.1 No No N/A No No
/dev/rmt*.2 Yes Yes N/A No No
/dev/rmt*.3 No Yes N/A No No
/dev/rmt*.4 Yes No N/A No No
/dev/rmt*.5 No No N/A No No
/dev/rmt*.6 Yes Yes N/A No No
/dev/rmt*.7 No Yes N/A No No
/dev/rmt*.104 No No N/A No No
/dev/rmt*.20 Yes No N/A No Yes
/dev/rmt*.40 Yes No N/A Yes No
/dev/rmt*.41 No No N/A Yes No
/dev/rmt*.60 Yes No N/A Yes Yes
/dev/rmt*.null5 Yes No N/A No No
/dev/rmt*.smc6 N/A N/A N/A N/A N/A
  1. The Rewind on Close special files for the Ultrium tape drives write filemarks under certain conditions before rewinding. See Opening the special file for I/O.
  2. The Retension on Open special files rewind the tape on open only. Retensioning is not completed because these tape products run the retension operation automatically when needed.
  3. The Bytes per Inch options are ignored for the tape devices that this driver supports. The density selection is automatic.
  4. The rmt*.10 file bypasses normal close processing, and the tape is left at the current position.
  5. The rmt*.null file is a pseudo device similar to the /dev/null AIX® special file. The IOCTL calls can be issued to this file without a real device that is attached to it, and the device driver returns a successful completion. Read and write system calls return the requested number of bytes. This file can be used for application development or debugging problems.
  6. The rmt*.smc file can be opened independently of the other tape special files.

For tape drives with attached SCSI medium changer devices, the rmt*.smc special file provides a separate path for issuing commands to the medium changer. When this special file is opened, the application can view the medium changer as a separate SCSI device.

This special file and the rmt* special file can be opened at the same time. The file descriptor that results from opening the rmt*.smc special file does not support the following operations.
  • Read
  • Write
  • Open in diagnostic mode
  • Commands that are designed for a tape device

If a tape drive has an attached SCSI medium changer device, all operations (including the medium changer operations) are supported through the interface to the rmt* special file.