You specify a tape or device to use for backup by supplying a logical device name. This name points to the subdirectory that contains the "raw" device file and includes the logical unit number of the drive. Tape drive naming conventions use a logical, not a physical, device name, as follows: /dev/rmt/N[d][b][n].
Raw magnetic tape subdirectory of the devices directory.
Drive number, with 0 as the first drive and n as the last drive.
Density which you can optionally specify by selecting one from the following choices:
l – low
m – medium
h – high
u – ultra
c – compressed
Optional character if you want to indicate the tape's BSD compatible behavior.
Optional character if you want to specify no-rewind. Omit this character to specify the default behavior, which is rewind.
If you don't specify the density, a tape drive typically writes at its preferred density, which is typically the highest density the tape drive supports. Most SCSI drives can automatically detect the density or format on the tape and read it accordingly. To determine the different densities that are supported for a drive, look at the /dev/rmt subdirectory. This subdirectory includes the set of tape device files that support different output densities for each tape.
Also, a SCSI controller can have a maximum of seven SCSI tape drives.
The following are examples of tape device names with corresponding rewind and density values.
/dev/rmt/0 – first drive, rewind. Preferred density is used.
/dev/rmt/0n – first drive, no rewind. Preferred density is used.
/dev/rmt/1m – second drive, medium density, rewind.
/dev/rmt/1hn – second drive, high density, no rewind.