Controlling tape drives

About controlling tape drives

You can control tape drives with the mt command to move and position the tape in several ways. This section describes how to perform the following tasks:

Move a tape to the end of data. You do this to append a backup.
Skip forward over files. You do this to access a particular tape file.
Skip backward over files. You do this to access a particular tape file.
Append a backup. You do this to save tape if you have small backups.
Rewind a tape. You do this to get to the beginning of the tape after using a no-rewind device.
Take a tape drive offline. You do this to service a tape drive.
Display status information. You do this to find out whether you can read the tape with a device or to verify that a tape drive is not in use.

The mt command syntax

The syntax of the mt command is as follows:

mt {-f|-t} device command [ count ]

The -f and -t options are interchangeable; they indicate that the next argument is a device.

device is a tape device.

command is an mt command. The following table discusses the most common mt commands.

count specifies the number of times to execute a command that supports multiple operations.

This section discusses the mt commands listed in the following table. For a description of all the mt commands, see the mt(1) man page.

Command	Task
`eom`	Position the tape to the end of the data or the end of the medium if the tape is full.
`fsf`	Move the tape forward, skipping a specified number of files.
`bsf`	Move the tape backward, skipping a specified number of files.
`rewind`	Rewind the tape.
`offline`	Rewind the tape and unload the tape medium if possible.
`status`	Display information about a device and the drive associated with it.

Note
Use nrst devices for all tape status and movement operations. Using other rewind types might produce unwanted side effects.

Caution
When you use the urst device with the mt command, the tape drives it is used with must be stackers and there must be sufficient tapes in the stacker sequence. Otherwise, the tape drives involved will terminate the command sequence or overwrite the same tape multiple times.

Moving a tape to the end of data

You move a tape to the end of data if you want to append data on a tape.

To move a tape to the end of data, or end of medium if the tape is full, complete the following step.

Step	Action
1	Enter the following command: *mt -f device* eom** device is the name of a no-rewind tape device.

Example

mt -f nrst0a eom

Note
If you use a rewind or unload/reload tape device, this command rewinds the device, moves the tape to the beginning of data, and unloads it if possible.

Moving forward to a file

You move forward to access a particular tape file further along the tape. You can skip over a specified number of file marks and stop at the end-of-tape side of a file mark. This puts the tape drive head at the beginning of a file.

To move forward to the beginning of a tape file, complete the following step.

Step	Action
1	Enter the following command: *mt -f device* fsf n** device is the name of a tape device used on the tape. n is the number of tape file marks you want to skip over going forward. The tape moves to the beginning of the nth file after the file where it is when the command is issued.

Example

If you enter the following command in the middle of the third file on the tape, it moves the tape to the beginning of the eighth file on the tape:

mt -f nrst0a fsf 5

Moving backward to the beginning of a file

You move backward to access a particular tape file further back on the tape.

To move backward to the beginning of a tape file, complete the following steps.

Step	Action
1	Enter the following command: *mt -f device* bsf n** device is the name of a tape device used on the tape. n is the number of tape file marks you want to skip over going backward. The tape moves to the beginning of the nth file before the file where it is when the command is issued.

Example

If you enter the following command in the middle of the fifth file on the tape, it moves the tape to the beginning of the second file on the tape:

mt -f nrst0a bsf 3

Rewinding a tape

You rewind a tape to get to the beginning of the tape when using a no-rewind device. You do this before performing a restore of a backup that was done using a no-rewind device, provided that there is no other data before the backed-up data on the tape and it is not unloaded.

To rewind a tape, complete the following step.

Step	Action
1	Enter the following command: *mt -f device* rewind** device is the name of a tape device used on the tape.

Example

mt -f nrst0a rewind

Taking a tape drive offline

You take a tape drive offline to service it.

To rewind the tape and take the tape drive offline by unloading the tape, complete the following step.

Step	Action
1	Enter the following command: *mt -f device* offline** device is the name of a tape device used on the tape.

Example

mt -f nrst0a offline

Displaying status information

You display status information to find out whether you can read with a device or to verify that a tape drive is not in use.

To display status information about a tape device and the drive associated with it, complete the following step.

Step	Action
1	Enter the following command: *mt -f device* status** device is the name of a tape device.

Example

mt -f nrst0a status

Result

A display like the following appears:

Tape drive: Quantum DLT7000

Status: ready, write enabled

Format: 85937 bpi 70 GB (w/comp)

fileno = 0  blockno = 95603  resid = 0

The fields in the display are as follows:

Tape drive--The model of the tape drive.
Status--Whether the tape drive is ready and write-enabled.
Format--The number of bytes per inch, total capacity in gigabytes, and whether data compression is used.
fileno--The current tape file number. Numbering starts at 0.
blockno--The current block number.
resid--The number of bytes that the drive attempted to write or read but could not because the end of tape was reached.