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Chapter 23. 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.

23.1. Types of tape devices

The following is a list of the different types of tape devices:

  • /dev/st0 is a rewinding tape device.
  • /dev/nst0 is a non-rewinding tape device. Use non-rewinding devices for daily backups.

There are several advantages to using tape devices. They are cost efficient and stable. Tape devices are also resilient against data corruption and are suitable for data retention.

23.2. 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

  • mt(1) and st(4) man pages

23.3. Writing to rewinding tape devices

A rewind tape device rewinds the tape after every operation. To back up data, you can use the tar command. By default, in tape devices the block size is 10KB (bs=10k). You can set the TAPE environment variable using the export TAPE=/dev/st0 attribute. Use the -f device option instead, to specify the tape device file. This option is useful when you use more than one tape device.

Prerequisites

  1. You have installed the mt-st package. For more information, see 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, overwrite it: 

    # tar -czf /dev/st0 _/source/directory

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

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

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

Additional resources

23.4. Writing to non-rewinding tape devices

A non-rewinding tape device leaves the tape in its current status, after completing the execution of a certain command. For example, after a backup, you could append more data to a non-rewinding tape device. You can also use it to avoid any unexpected rewinds.

Prerequisites

  1. You have installed the mt-st package. For more information, see Installing tape drive management tool.

  2. Load the tape drive: 

    # mt -f /dev/nst0 load

Procedure

  1. Check the tape head of the non-rewinding tape device /dev/nst0: 

    # mt -f /dev/nst0 status

  2. Specify the pointer at the head or at the end of the tape: 

    # mt -f /dev/nst0 rewind

  3. Append the data on the tape device: 

    # mt -f /dev/nst0 eod
# tar -czf /dev/nst0 /source/directory/

  4. Back up the /source/directory/ to the tape device: 

    # tar -czf /dev/nst0 /source/directory/
tar: Removing leading `/' from member names
/source/directory/
/source/directory/man_db.conf
/source/directory/DIR_COLORS
/source/directory/rsyslog.conf
[...]

  5. View the status of the tape device: 

    # mt -f /dev/nst0  status

Verification steps

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

    # tar -tzf /dev/nst0
/source/directory/
/source/directory/man_db.conf
/source/directory/DIR_COLORS
/source/directory/rsyslog.conf
[...]

Additional resources

23.5. Switching tape head in tape devices

Use the following procedure to switch the tape head in the tape device.

Prerequisites

  1. You have installed the mt-st package. For more information, see Installing tape drive management tool.
  2. Data is written to the tape device. Fore more information, see Writing to rewinding tape devices or Writing to non-rewinding tape devices.

Procedure

  • To view the current position of the tape pointer: 

    # mt -f /dev/nst0 tell

  • To switch the tape head, while appending the data to the tape devices: 

    # mt -f /dev/nst0 eod

  • To go to the previous record: 

    # mt -f /dev/nst0 bsfm 1

  • To go to the forward record: 

    # mt -f /dev/nst0 fsf 1

Additional resources

  • mt(1) man page

23.6. Restoring data from tape devices

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

Prerequisites

  1. You have installed the mt-st package. For more information, see Installing tape drive management tool.
  2. Data is written to the tape device. For more information, see Writing to rewinding tape devices or Writing to non-rewinding tape devices.

Procedure

  • For rewinding tape devices /dev/st0:

    • Restore the /source/directory/: 

      # tar -xzf /dev/st0 /source/directory/

  • For non-rewinding tape devices /dev/nst0:

    • Rewind the tape device: 

      # mt -f /dev/nst0 rewind

    • Restore the etc directory: 

      # tar -xzf /dev/nst0 /source/directory/

Additional resources

  • mt(1) and tar(1) man pages

23.7. Erasing data from tape devices

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

Prerequisites

  1. You have installed the mt-st package. For more information, see Installing tape drive management tool.
  2. Data is written to the tape device. For more information, see Writing to rewinding tape devices or Writing to non-rewinding 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

  • mt(1) man page

23.8. Tape commands

The following are the common mt commands:

Table 23.1. mt commands

CommandDescription

mt -f /dev/st0 status

Displays the status of the tape device.

mt -f /dev/st0 erase

Erases the entire tape.

mt -f /dev/nst0 rewind

Rewinds the tape device.

mt -f /dev/nst0 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/nst0 bsfm n

Switches the tape head to the previous record.

mt -f /dev/nst0 eod

Switches the tape head to the end of the data.