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System Administration Guide: Devices and File Systems
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Backup Device Names

You specify a tape or diskette 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. The following table shows this naming convention.

Table 30-2 Basic Device Names for Backup Devices

Device Type






In general, you specify a tape device as shown in the following figure.

Figure 30-1 Tape Drive Device Names
Illustration shows logical tape device name that includes magnetic tape device directory, drive, and the optional density values.

If you don't specify the density, a tape drive typically writes at its “preferred” density. The preferred density usually means 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.

Specifying the Rewind Option for a Tape Drive

Normally, you specify a tape drive by its logical unit number, which can run from 0 to n. The following table describes how to specify tape device names with a rewind or a no-rewind option.

Table 30-3 Specifying Rewind or No-Rewind for a Tape Drive

Drive and Rewind Value

Use This Option

First drive, rewind


First drive, no rewind


Second drive, rewind


Second drive, no rewind


Specifying Different Densities for a Tape Drive

By default, the drive writes at its “preferred” density, which is usually the highest density the tape drive 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. The following table describes how to specify different densities for a tape drive.

Table 30-4 Specifying Different Densities for a Tape Drive

Drive, Density, and Rewind Value

Use This Option

First drive, low density, rewind


First drive, low density, no rewind


Second drive, medium density, rewind


Second drive, medium density, no rewind


The additional density values are shown in Backup Device Names.

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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire