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Thresholds During a Read Operation
The motion threshold controls the starting and stopping of tape
motion. The reconnect threshold controls the rate of disconnects and
reconnects between the tape drive and the initiator.
Motion Threshold
In a start/stop read operation, the tape-to-buffer transfer speed is
faster than the buffer-to-initiator transfer speed. In this mode of
operation, the motion threshold value represents the minimum
amount of free space that must be in the tape drive’s 1-MByte buffer
before tape motion will start and data will be read from the tape to
the buffer. The read-from-tape operation continues until the buffer is
full and tape motion stops. Tape motion does not restart until the
amount of free space in the buffer once again exceeds the motion
threshold value.
Reconnect Threshold
In a streaming read operation, the tape-to-buffer transfer rate is equal
to or less than the buffer-to-initiator transfer rate. In this mode of
operation, the tape drive reads data from tape continually. When the
buffer becomes empty, the tape drive disconnects from the initiator,
and the initiator is free to perform other tasks.
For the tape drive to continue streaming, the initiator must begin to
accept data again before the buffer is full. The reconnect threshold
valuerepresentstheminimumamountofdatathatmustbeinthe
tape drive’s 1-MByte buffer before the tape drive will reconnect to the
initiator to transfer data from the buffer. When the reconnect
threshold value is exceeded, the tape drive reconnects to the initiator
and data transfer resumes. The data transfer to the initiator continues
until the buffer is empty.
3-8 EXB-8205 and EXB-8505 510504
(Standard and XL)
3 Functional Description