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The IDD does not perform data transfer immediately after receiving the CDB, but after
performing automatic disconnect processing once, it executes pre-fetching of data. If
disconnect processing is permitted, the IDD either completes transfer of all the data specified
in the command or, at the point when the empty space in the data buffer runs out, disconnect
processing is executed. Positioning of the specified data blocks is performed in parallel with
this data transfer, and writing of data from the data buffer to the disk media is executed
immediately after positioning is completed. See Section 2.1 "Data Buffer" for details of data
buffer operation and control of the timing for starting reconnection processing by the MODE
SELECT parameter (buffer empty ratio).
If the write cache function is enabled, the IDD reports a status byte at the point when reception
of all the data transferred from the INIT is completed. If an error occurs while data are being
written to the disk media, a CHECK CONDITION status is reported for the command to be
executed next. If the write cache function is disabled, a status byte is reported after writing to
the disk media of all the data transferred from the INIT is completed, then execution of the
command is terminated.
Note:
Even when there is an error in the specification in the CDB, or when a write operation to
the disk media cannot be executed normally due to various other causes, the transfer of
data (data is pre-fetched to the data buffer) from the INIT to the IDD may be executed. In
this case, the length of data transferred from the INIT to the IDD is undefined. Also, all
the data transferred to the IDD will not necessarily be actually written to the disk media.
However, if the command is terminated with a CHECK CONDITION status and the sense
key of the sense data indicates "ILLEGAL REQUEST [=5]," the data from that command
is not written to the disk media by a write operation.
C141-E039-01EN
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