Exabyte EXB-8505 8mm manual Streaming and Start/Stop Modes, Data Compression Monitoring

3Functional Description

Data Compression Monitoring

The tape drive constantly monitors the compression ratio to determine whether compressing the data will actually decrease the size of the data set. When a logical block expands (as it might, for example, when it has already been compressed by the initiator), the tape drive automatically switches to uncompressed format. It remains in this format until it encounters a compressible logical block. Then, it switches back to the compressed format.

Streaming and Start/Stop Modes

The data buffer enables the tape drive to operate as either a streaming tape device or as a start/stop tape device. When the tape drive transfers data to the 1-MByte data buffer, the data buffer’s formatter performs the following tasks:

Formats logical user data blocks into physical blocks

Appends tag, address, and index information to each data block

The mode of operation (streaming or start/stop) depends on the rate that data can be transferred between the initiator and the tape drive, as follows:

The tape drive operates in streaming mode if the initiator can sustain a minimum of:

∙1 MByte per second for 8500c format (EXB-8505 and EXB-8505XL only)

∙500 Bytes per second for 8500 format (EXB-8505 and EXB-8505XL only)

∙500 KBytes per second for 8200c format

∙262.5 KBytes per second for 8200 format

Note: These values assume a 2:1 compression ratio for 8500c and 8200c formats.

The tape drive operates in start/stop mode if the initiator cannot sustain these minimum transfer rates; starting and stopping occur automatically.

3-4	EXB-8205 and EXB-8505	510504
	(Standard and XL)