Fujitsu MAA3182FC Series, Manual

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C141-E054-02EN 3 - 3
IMPORTANT
In order to avoid frequent repetition of the Loop CLOSE/OPEN
processing after data frame transfer starts on the FC interface,
and avoid the occurrence of data overruns, it is necessary to set
the buffer full ratio (see Section 3.1.2) of the MODE SELECT
parameter so the difference in the data transfer rates between the
INIT (FC interface) and the disk drive is maintained in a good
balance.
Figure 3.2 shows an example of the data buffer operating state during a read operation.
Details are explained in Section 3.1.2.
Figure 3.2 Example of data buffer operation during read
(2) Write operation
After data transferred from the INIT are stored temporarily in the data buffer, they are written
to the disk media. The basic write operation procedure is as shown below.
1) When the IDD receives a command, it transfers the XFER_RDY flame to INIT. Later it
stores data transferred from the INIT to the data buffer (data pre-fetch). At this time, the
IDD locates the position of the data block on the disk media specified by the command in
parallel.
When storing of all the size of data specified in the XFER_RDY flame in the data buffer is
completed, the IDD performs Loop CLOSE processing.
2) When locating of the target data block on the disk media is completed, the IDD writes the
data in the data buffer to the disk media. If the target data block location operation is
completed during the data pre-fetch processing in 1), writing of data to the disk media is
performed in parallel with the data pre-fetch to the data buffer.
3) If the data transfer rate of the INIT (FC interface) is lower than the data transfer rate of the disk
drive, since the data pre-fetch of data that are to be written to that data block is not completed, it