Exabyte EXB-8205 Instruções de Operação descarregar pdf (Página 75)

3. The third physical block written to tape contains 1,024 bytes of

data from the host.

4. The fourth physical block contains 512 bytes of host data and

512 gap bytes.

5. The pattern is repeated until all of the logical blocks are written.

Because the block size (1,536 bytes) is not an exact multiple of 1,024,

tape capacity is reduced by the addition of gap bytes. In this case,

approximately one-fourth of the available tape capacity is wasted.

Logical Block Packing: All Other Data Formats

The maximum amount of data that can be placed in a physical block

to be written to tape in all CTS data formats is 1,024 bytes. However,

unlike a physical block of data in 8200 format, a physical block of data

in all other formats (8200c, 8500, and 8500c) can contain one or more

logical blocks of data from the host. For example, if a logical block

from the host is 512 bytes, the CTS places two of the 512-byte blocks

in the physical block it writes to tape.

In each of these data formats, a logical block can start in one physical

block and end in another physical block. For example, if a logical

block from the host is 3,000 bytes, the CTS places 1,024 bytes in the

first physical block, 1,024 bytes in the second physical block, and 952

bytes in the third physical block. The next 3,000-byte logical block

from the host starts immediately following the 952 bytes in the third

physical block. Because no gap bytes are added to physical blocks,

tape capacity is not significantly affected by the size of physical block

sent by the host.

Although logical block packing prevents the loss of significant tape

capacity, slight capacity may be lost when small block sizes are used.

When packing more than two logical blocks in a single physical block,

the CTS adds a two-byte header to each logical block after the second

block.

May 1994 EXB-8205 and EXB-8505

(Standard and XL)

3-13

3 Implementing CTS Operations

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