C141-E054-02EN
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IMPORTANT
If transfer of this page descriptor is required by the MODE
SENSE or MODE SENSE EXTENDED command, the IDD reports
X '0E' as the page length (byte 1). However, if either X '0E' or X
'0A' is specified for the page length in the MODE SELECT
command, the IDD regards it as if the correct page length was
specified. The X '0A' page length, is provided in consideration of
compatibility with previous models, but it is recommended that
the page length X '0E' be used by the INIT to support expansions
in the specifications in the future.
See Section 2.1, "Data Buffer" concerning specification methods for the "Buffer Full Ratio" and
"Buffer Empty Ratio" parameters in this page descriptor and details of data buffer operation.
a. Buffer full ratio
This parameter specifies the timing for the IDD to start Loop OPEN processing in order to
transfer data to the INIT by the READ or READ EXTENDED command.
The value specified in this parameter (n) shows the amount of data read to the IDD's data
buffer from the disk media as a proportion [n/256] of the total capacity of the data buffer
until it opens the loop for transferring the data on the FC bus is started. The IDD's default
segment capacity is 127 KB (MAA3182FC) and 486 KB (MAF3364FC, MAG3091FC,
MAG3182FC). Therefore, if the specified value (n) is 128, for example, it means that a
data volume of 63.5 KB was specified. (
Note
)
If it is possible to transfer the amount of data specified in this parameter to the INIT from
the data buffer, opens the loop and transfer of data to the INIT begins.
The default value for this parameter is X '20.' It is possible to specify X '00' in this
parameter, but the minimum effective value of the buffer full ratio is 1 logical data block,
so specifying X '00' is equivalent to specifying the value for 1 logical data block. (
Note
)
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.
The value specified in this parameter (n) indicates the size of the empty area in the IDD's
data buffer as a proportion of the total data buffer capacity of the IDD [n/256]. IDD
segment buffer length is 127 KB (MAA3182FC) and 486 KB (MAF3364FC,
MAG3091FC, MAG3182FC). For example, if the specified value (n) is 128 and the
number of cache segments is 4 (this is the default value), the size of the empty space in the
buffer is specified as 63.5 KB. (
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 opens the loop, requesting transfer of the succeeding data.
Содержание MAA3182FC Series
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