Seagate STT20000A Product Manual page 75

Tape Format
STT20000A Product Manual
Frames are numbered indirectly using the 26 most significant bits of the Physical
Block Address. Frame operation is controlled by the drive and generally invisible to
the host. Frames are used primarily as a means to control the error correction
operations.
Frames can be overwritten with new data frames or an end-of-data (EOD) frame.
Append operations can only begin at EOD.
An underrun is not allowed in the middle of a frame, regardless of the frame type.
Filler blocks can be used to complete a frame as long as they are not used interior
to a logical block.
A frame that cannot be completed on one track is rewritten in its entirety at the
beginning of the following track. Frames are not split around corner turns.
The general frame layout—108 data blocks and 20 ECC blocks—is illustrated in
Figure 6-2.
Figure 6-2
General frame layout
Data Data Data
Block Block Block
0 1 2
The four types of frames are as follows:
•
Data frames contain data and information blocks in addition to ECC blocks.
•
The Media Header frame contains only Media Header blocks and ECC blocks.
This frame is recorded as the first frame on the Directory Track.
•
Track ID frames are recorded as part of the pre-formatting process of the
cartridge. These frames are easily distinguished from other frame types
because they reside entirely outside of the data region of the tape.
•
An EOD frame is an absolute indicator of the end of the recorded data. It is
recorded after the last frame containing host data upon terminating a Write
process.
... Data ECC
Block Block
107 0
Chapter 6
ECC ... ECC
Block Block
1 19
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