Exabyte EXB-8205 Instrucciones de operaciones descargar pdf (Pagina 34)

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Physical Blocks Each physical track contains eight physical

blocks. A physical block containing user data includes the

following:

14 bytes of header information

Up to 1,024 bytes of user data

2 bytes of cyclic redundancy check (CRC) data

400 bytes of error correction code (ECC) data

Note that the header, ECC data, and CRC data do not affect the

user data capacity of the tape.

Since each physical track contains eight 1,024-byte physical blocks,

each track can contain a maximum of 8,192 uncompressed bytes of

user data. Assuming an average compression ratio of 2:1, each track

written in a compressed format can contain 16,384 compressed bytes

of user data. (The actual compression ratio depends on the type of

data.)

Each 1,024-byte physical block can contain multiple logical blocks

(for example, two uncompressed 512-byte logical blocks can be

written in one physical block). In addition, a logical block can start

in one physical block and end in a subsequent physical block. This

logical block packing prevents the loss of data capacity for tapes

with small logical blocks.

Note: In 8200 format, only one logical block can be written in each

physical block.

Servo Areas

Data tracks contain servo areas that the CTS uses to read tapes

written by other CTSs. Each servo area contains a signal that the

servo head uses to control linear tape velocity. This process results

in accurate positioning of the track under the read head. In 8500c

and 8500 format, servo areas are placed at the beginning, middle,

and end of every other track. In 8200c format, servo areas are placed

at the beginning, middle, and end of each track. In 8200 format,

servo areas are placed at the beginning of each track.

1-12

EXB-8205 and EXB-8505

(Standard and XL)

510503

1 CTS Features

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 445 446

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Exabyte EXB-8205 Instrucciones de operaciones Pagina 34

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