You specify a tape or diskette drive to use for backup by supplying a logical device name. This name points to the subdirectory containing 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. Table 38-2 shows this naming scheme.
Table 38-2 Basic Device Names for Backup Devices
Device Type |
Name |
---|---|
Tape |
/dev/rmt/n |
Diskette |
/vol/dev/rdiskette0/unlabeled |
In general, you specify a tape drive device as shown in Figure 38-1.
If you don't specify the density, a tape drive will typically write at its "preferred" density, which usually means the highest density it supports. Most SCSI drives can automatically sense 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, which 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.
Normally, you specify a tape drive by its logical unit number, which may run from 0 to n. Table 38-3 describes how to specify tape device names using default density settings.
Table 38-3 Specifying Default Densities for a Tape Drive
To Specify The ... |
Use ... |
---|---|
First drive, rewinding |
/dev/rmt/0 |
First drive, nonrewinding |
/dev/rmt/0n |
Second drive, rewinding |
/dev/rmt/1 |
Second drive, nonrewinding |
/dev/rmt/1n |
By default, the drive writes at its "preferred" density, which is usually the highest density it supports. If you do not specify a tape device, the command writes to drive number 0 at the default density the device supports.
To transport a tape to a system whose tape drive supports only a certain density, specify a device name that writes at the desired density. Table 38-4 describes how to specify different densities for a tape drive.
Table 38-4 Specifying Different Densities for a Tape Drive
To Specify The ... |
Use ... |
---|---|
First drive, low density, rewinding |
/dev/rmt/0l |
First drive, low density, nonrewinding |
/dev/rmt/0ln |
Second drive, medium density, rewinding |
/dev/rmt/1m |
Second drive, nonrewinding, medium density |
/dev/rmt/1mn |
The unit and density characters are shown in Figure 38-1.