Chapter 18. Managing tape devices

A tape device is a magnetic tape where data is stored and accessed sequentially. Data is written to this tape device with the help of a tape drive. There is no need to create a file system in order to store data on a tape device. Tape drives can be connected to a host computer with various interfaces like, SCSI, FC, USB, SATA, and other interfaces.

The following are the different types of tape devices:

  • /dev/st is a rewinding tape device.
  • /dev/nst is a non-rewinding tape device. Use non-rewinding devices for daily backups.

Advantages of tape devices:

  • Cost efficient
  • Resilient against data corruption
  • Data retention
  • Stable

18.1. Installing tape drive management tool

Use the mt command to wind the data back and forth. The mt utility controls magnetic tape drive operations and the st utility is used for SCSI tape driver. This procedure describes how to install the mt-st package for tape drive operations.

Procedure

  • Install the mt-st package: 

    # yum install mt-st

Additional resources

  • The mt man page.
  • The st man page.

18.2. Writing to tape devices

This procedure describes how to back up data using the tar command. By default, block size is 10KB (bs=10k) in tape devices. The -f device option specifies the tape device file, but this option is not required if you have set the TAPE environment variable using the export TAPE=/dev/st0 attribute.

Prerequisites

  1. The mt-st package is installed. For more information, see Section 18.1, “Installing tape drive management tool”.

  2. Load the tape drive: 

    # mt -f /dev/st0 load

Procedure

  1. Check the tape head: 

    # mt -f /dev/st0 status

SCSI 2 tape drive:
File number=-1, block number=-1, partition=0.
Tape block size 0 bytes. Density code 0x0 (default).
Soft error count since last status=0
General status bits on (50000):
 DR_OPEN IM_REP_EN

    Here:

    • the current file number is -1.
    • the block number defines the tape head. By default, it is set to -1.
    • the block size 0 indicates that the tape device does not have a fixed block size.
    • the Soft error count indicates the number of encountered errors after executing the mt status command.
    • the General status bits explains the stats of the tape device.
    • DR_OPEN indicates that the door is open and the tape device is empty. IM_REP_EN is the immediate report mode.

  2. If the tape device is not empty, specify the tape head: 

    # mt -f /dev/st0 rewind

# tar -czf /dev/st0 /etc

    This command overwrites the data on a tape device with the content of the /etc directory

    Optional: To append the data on the tape device: 

    # mt -f /dev/st0 eod

  3. Back up the /etc directory to the tape device: 

    # tar -czf /dev/st0 /etc
tar: Removing leading `/' from member names
/etc/
/etc/man_db.conf
/etc/DIR_COLORS
/etc/rsyslog.conf
[...]

  4. View the status of the tape device: 

    # mt -f /dev/st0  status

Verification steps

  • View the list of all files on the tape device: 

    # tar -tzf /dev/st0
/etc/
/etc/man_db.conf
/etc/DIR_COLORS
/etc/rsyslog.conf
[...]

Additional resources

18.3. Switching tape head in tape devices

Use the following procedure to switch the tape head in the tape device. While appending the data to tape devices, use the eod option to switch the tape head.

Prerequisites

  1. The mt-st package is installed. For more information, see Section 18.1, “Installing tape drive management tool”.
  2. Data is written to the tape device. Fore more information, see Section 18.2, “Writing to tape devices”.

Procedure

  • To go to the end of the data: 

    # mt -f /dev/st0 eod

  • To go to the previous record: 

    # mt -f /dev/st0  bsfm 1

  • To go to the forward record: 

    # mt -f /dev/st0  fsf 1

Additional resources

  • The mt man page.

18.4. Restoring data from tape devices

To restore data from a tape device, use the tar command.

Prerequisites

  1. The mt-st package is installed. For more information, see Section 18.1, “Installing tape drive management tool”.
  2. Data is written to the tape device. Fore more information, see Section 18.2, “Writing to tape devices”.

Procedure

  1. Rewind the tape device: 

    # mt -f /dev/st0 rewind

  2. Restore the /etc directory: 

    # tar -xzf /dev/st0 /etc

Additional resources

  • The mt man page.
  • The tar man page.

18.5. Erasing data from tape devices

To erase data from a tape device, use the erase option.

Prerequisites

  1. The mt-st package is installed. For more information, see Section 18.1, “Installing tape drive management tool”.
  2. Data is written to the tape device. Fore more information, see Section 18.2, “Writing to tape devices”.

Procedure

  1. Erase data from the tape device: 

    # mt -f /dev/st0 erase

  2. Unload the tape device: 

    mt -f /dev/st0 offline

Additional resources

  • The mt man page.

18.6. Tape commands

The following are the common mt commands:

Table 18.1. mt commands

CommandDescription

mt -f /dev/st0 status

Displays the status of the tape device.

mt -f /dev/st0 rewind

Rewinds the tape device.

mt -f /dev/st0 erase

Erases the entire tape.

mt -f /dev/st0 fsf n

Switches the tape head to the forward record. Here, n is an optional file count. If a file count is specified, tape head skips n records.

mt -f /dev/st0 bsfm n

Switches the tape head to the previous record.

mt -f /dev/st0 eod

Switches the tape head to the end of the data.