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Chapter 6 Tape format
Page 66 STT8000A Product Manual
Blocks
Information in the Block Control byte determines the type of block being recorded
except for ECC blocks which are recognized by their block numbers. Also,
information about the number of user data bytes available in each data block is
recorded in the Block Control byte of the block.
The Data Field of the blocks always contain 512 bytes. However, the number of
valid data bytes in the block may be less than 512.
The seven different types of blocks are as follows:
•
Data blocks
contain user data. A full Data block contains 512 bytes; however,
data block can contain from 1 through 511 valid data bytes depending on the
selected logical block size of the host.
•
Media Header blocks
contain specific host., drive, and vendor information as
well as the Volume Directory. The first frame on the Directory Track is teh Media
Header Frame. This frame contains 52 Media Header blocks (plus the normal
12 ECC blocks).
•
Information blocks
—Filemark blocks, Setmark blocks, and Cancelmark
blocks—contain specific types of information. Filemark blocks are physical
blocks written to tape in response to a host WRITE FILEMARKS command.
Setmark blocks are physical blocks written to tape in response to a host WRITE
SETMARKS command. Cancelmark blocks are physical blocks written to tape
under firmware control.
•
Filler blocks
contain no valid information in the data area. These blocks are
used to fill incomplete frames.
•
EOD
blocks
are absolute indicators of the end of recorded data.
•
ECC blocks
contain error correction parity bytes that are used to ensure data
integrity during read operations.
•
Track ID
blocks are recorded as part of the pre-formatting process of the
cartridge.
Tape reference servo pattern
To increase track density, a track servo reference pattern is prerecorded on the tape
at the factory. The pattern is recorded referenced to servo patterns in the region
between the beginning-of-tape (BOT) hole and the load point market (LP) hole. The
same pattern is recorded between the end-of-tape (EOT) hole and the early warning
(EW) hole. The servo pattern is written across the entire width of the tape.