Blocks; Tape Reference Servo Pattern - Seagate STT20000A Product Manual

Chapter 6

Blocks

Tape reference servo pattern

Page 68
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 the Media
Header Frame. This frame contains 108 Media Header blocks (plus the normal
20 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.
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.
Tape Format
STT20000A Product Manual