Tandberg Data SLR7-140 PROGRAMMER, Руководство пользователя

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Tandberg Data About Tape Streamers
2-19 Tandberg SLR Product Line SCSI Functional Specifications
If the actual block length is larger than the expected
block length, the READ command will transfer the
expected number of bytes only. The READ command is then
terminated with a CHECK CONDITION Status. The Illegal
Length Indicator will be set in the Sense Data List. If
the fixed-bit is cleared, the Information bytes will be
set up with the difference between the expected number
of bytes and the actual number of bytes. This will be a
negative number in this case. The information bytes are
presented as a 32 bit 2's complement number. If the
fixed-bit is set, the Information bytes will be set up
with the difference between the specified number of
blocks and the actual number of blocks transferred. The
block with the unexpected length is counted among the
transferred blocks even if its length was wrong. Note
that this means that the Information Bytes may read zero
even if the READ command was terminated with CHECK
CONDITION and Illegal Length Indication. The logical
tape position will be at the beginning of the block
following the block with the unexpected length. This
means that the additional bytes in the block with the
unexpected length are lost.
2.7. Data Buffering
2.7.1. Introduction
The Drive has a temporary storage area capable of
holding one or more blocks or tapemarks – a data buffer.
The data buffer may hold any combination of data blocks
and tapemarks in the process of being written to the
recording medium, or it may contain read-ahead data
blocks and tapemarks transferred from the recording
medium.
The data buffer operates as a FIFO queue, compensating
for the different transfer rates on the SCSI-bus and the
tape system. The Drive is usually only connected to the
SCSI-bus for short amounts of time when bursts of data
are transferred at a much higher speed than the normal
tape transfer rate. The data buffer can be in one out of
two modes; read mode or write mode. The data buffer is
in write mode when executing WRITE or WRITE FILEMARKS
commands. The data buffer is in read mode when executing
LOCATE, READ, SPACE or VERIFY
1
commands.
1
VERIFY is not supported by SLR7 and SLR140