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Read Operations
Figure 3-2 provides a high-level overview of the tape drive’s flow of
data during a read operation.
The process for reading logical blocks of user data is outlined below.
¬ The tape drive reads data from tape, uses ECC to correct errors
as necessary for each physical block, and transfers data to the
data buffer. The read operation continues until the buffer is full
and tape motion stops.
If the data has not been compressed, the data goes directly from
thedatabuffertotheSCSIbus.
If the data has been compressed, the data goes from the data
buffer to the decompression circuit to be decompressed. Then,
the decompressed data is sent to the SCSI bus.
In either case, the 2-byte logical block CRC, which was
appended when the data was written, is again verified. This
final integrity check assures that all block reconstruction and
decompression was successful.
Uncompressed data
SCSI
bus
1
Decompression
circuit
Data to be
decompressed
Data
buffer
Data read from tape
Ta p e
2
Figure 3-2 Data flow during a read operation
May 1994 EXB-8205 and EXB-8505 3-7
(Standard and XL)
3 Functional Description