Exabyte EXB-8205 Instruções de Operação descarregar pdf (Página 79)

3.6 Using Streaming vs. Start/Stop Mode

The CTS includes a 1-MByte data buffer that enables it to operate as

either a streaming tape device or as a start/stop tape device, depending

on the rate of data transfer to and from the host system. If your

system permits, operating the CTS in streaming mode can maximize

the amount of data you can store on a tape and minimize the amount

of wear on the tape and recording heads.

Streaming Mode

When the CTS is operating in streaming mode, it transfers data

continuously between the buffer and tape without stopping tape

motion. During a write operation, if the CTS’s buffer fills with data

from the host faster than the CTS can write the data to tape, the CTS

disconnects from the SCSI bus while continuing to write data to tape

until the buffer has emptied to a certain level (the reconnect threshold).

Then the CTS reconnects to the SCSI bus to accept more data.

Similarly, during a read operation, if the host can accept data from the

CTS’s buffer faster than the CTS can fill the buffer with data from the

tape, the CTS disconnects from the SCSI bus until the buffer is refilled

to the reconnect threshold while continuing to read data into the

buffer. Then the CTS reconnects to the SCSI bus to transfer more data.

Start/Stop Mode

When the CTS is operating in start/stop mode, it must stop and

restart tape motion during read and write operations to accommodate

the slower data transfer rate of the host.

During a write operation, the CTS waits until the buffer is filled to a

certain level (the motion threshold), starts the tape, records the buffered

data, then stops the tape until the buffer can be filled to that level

again by the host.

During a read operation, the CTS fills the buffer with data from the

tape, stops the tape, waits for the host to accept enough data to empty

the buffer to the motion threshold, then starts the tape and fills the

buffer again.

May 1994 EXB-8205 and EXB-8505

(Standard and XL)

3-17

3 Implementing CTS Operations

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Exabyte EXB-8205 Instruções de Operação Página 79