Datasheet

3.2 Look-Ahead Cache Feature
C141-C008 3-7
b. Buffer empty ratio
This parameter specifies the timing for the IDD to start Loop OPEN
processing 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].
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 Loop OPEN 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 which is the nearest data block boundary.
Also, if zero is specified in any of these parameters, the IDD treats that
parameter as though 1 logical data block has been specified.
3.2 Look-Ahead Cache Feature
In order to use the data buffer more effectively and improve the disk drive's
effective access speed, the IDD is equipped with a simple cache feature called a
"Look-Ahead Cache Feature." The Look-Ahead cache feature is an effective,
simple cache function for an INIT which reads data block groups on the disk
media sequentially using multiple commands.