8.7 Using the tctl Command to Take a Tape Device Off-Line

8.8 rmt Special File Notes

The purpose of the device rmt is to provides access to the sequential-access bulk storage medium device driver.

Magnetic tapes are used primarily for backup, file archives, and other off-line storage. Tapes are accessed through the /dev/rmt0, ..., /dev/rmt255 special files. The r in the special file name indicates raw access through the character special file interface. A tape device does not lend itself well to the category of a block device. Thus, only character interface special files are provided.

In Table 31 is a list of the tape device special file characteristics; /dev/rmt* can be from /dev/rmt0 to /dev/rmt255.


Table 31: Tape Device Special File Characteristics

The following can be said about the characteristics shown:

• The values of density setting #1 and density setting #2 come from tape drive attributes that can be set using SMIT. Typically, density setting #1 is set to the highest possible density for the tape drive, while density setting #2 is set to a lower density. However, density settings are not required to follow this pattern.

• The density value (bytes per inch) is ignored when using a magnetic tape device that does not support multiple densities. For tape drives that do support multiple densities, the density value only applies when writing to the tape. When reading, the drive defaults to the density at which the tape is written.

• Most tape drives use a 512-byte block size. The 8mm tape drive uses a minimum block size of 1024 bytes. Using SMIT to lower the block size may waste space.

8.9 High Availability Cluster Multi-Processing