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C141-E124-01EN2 - 6
is performed when it becomes possible to transfer 2 blocks of data [16 x (32/256)], from the
data buffer.
b. Buffer empty ratio
This parameter specifies the timing for the IDD to start reconnection when it is requested by
the INIT to transfer data in the WRITE, WRITE EXTENDED or WRITE AND VERIFY
command. In a write operation, after the IDD receives a command, the IDD begins transferring
data (data pre-fetch) while locating the position of the target data blocks on the disk media in
parallel. Therefore, if the total number of bytes of data specified in the command is less than
the capacity of a cache segment, all the data are pre-fetched in a batch, so the specification in
this parameter is not applied.
The value specified in this parameter (n) indicates a proportion of the total data buffer capacity
of the IDD when the buffer is empty [n/256]. (
Note
)
While the IDD is writing data to the disk media, it is using the data pre-fetched to the data
buffer in order and when the empty space in the data buffer reaches the amount specified in
this parameter, it executes reconnection processing, requesting transfer of the succeeding data.
However, if the number of data blocks remaining to be transferred according to the command
being executed does not reach the amount of data specified in this parameter, the IDD executes
reconnection processing at the point when the number of data blocks remaining in the data
buffer's empty space reaches the specified number of data blocks and requests transfer of the
succeeding data.
Note:
If the value specified for the "buffer full ratio" or the "buffer empty ratio" is not within
double the integral boundary of the logical data block length, the IDD rounds up the
specified value to the nearest data block boundary. In addition, if zero is specified for any
of these parameters, the IDD an appropriate value for the parameter that is determind by
IDD.