This article assumes that you have mt installed on your system.
For RHEL/CentOS this can be installed using the following command

# yum install mt-st

For FreeBSD mt can be installed using the following command

# pkg_add -r mt

For other distributions refer their respective documentation

In the examples below we have used both the rewind and no-rewind tape devices. For understanding the difference between the two seeĀ http://www.sprillion.com/rewind-vs-norewind-st0-vs-st1.html

Obtaining the current status of the tape drive

mt -f <tape device> status
For example:
# mt -f /dev/st0 status
SCSI 2 tape drive:
File number=-1, block number=-1, partition=0.
Tape block size 262144 bytes. Density code 0x4a (no translation).
Soft error count since last status=0
General status bits on (1010000):
 ONLINE IM_REP_EN

Changing the default block size

Setting a block of zero indicates a variable block size. Any other positive value indicates a fixed block size. Block size should be within the minimum and maximum block size for the tape drive

mt -f <tape device> setblk <block size> (On Linux)
mt -f <tape device> blocksize <block size> (On FreeBSD)
For example
mt -f /dev/st0 setblk 65536 (Fixed block size of 64K)
mt -f /dev/st0 setblk 0 (Variable block size

Enabling and Disabling Compression

mt -f <tape device> compression 0 (Disable Compression)
mt -f <tape device> compression 1 (Enable Compression)

For example:
To disable compression for /dev/st0
#mt -f /dev/st0 compression 0

Rewinding the tape

mt -f <tape device> rewind

Erasing a tape

mt -f <tape device> erase
For example:
# mt -f /dev/st0 rewind (Position at the beginning of the tape)
# mt -f /dev/st0 erase (Erase the entire tape)

Most tape drives can erase from the current position of the tape. However some tape drives will refuse to erase from any position other than the beginning of the tape.

Spacing over blocks

Forward spacing is accomplished by the fsr option and backward spacing is accomplished by using the bsr option

For example the following command spaces forward over one record
# mt -f /dev/nst0 status
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 262144 bytes. Density code 0x4a (no translation).
Soft error count since last status=0
General status bits on (41010000):
# mt -f /dev/nst0 fsr 1
# mt -f /dev/nst0 status
SCSI 2 tape drive:
File number=0, block number=1, partition=0.
Tape block size 262144 bytes. Density code 0x4a (no translation).
Soft error count since last status=0
General status bits on (1010000):
 ONLINE IM_REP_EN

Similarly fsf is used to forward space over filemarks, bsf is used to backward space over filemarks.

Further Information

Refer the man page of mt