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Fibre Channel Interface Manual, Rev. D 209
Mode Select Page Headers And Their Parameters
See Mode Sense command (see Section 12.13) for detailed descriptions.
Number of Blocks
This field contains the number of accessible logical blocks on the logical unit. The maximum Number of Blocks depends on
the Block Length in the Block Descriptor, the Format parameters, and the Rigid Disc Drive Geometry parameters. A drive
not having the capacity programming feature will ignore the Number of Blocks field and will always have the maximum
Number of Blocks.
Drives that have the capacity programming feature set the Number of Blocks to the maximum value if the Number of Blocks
field contains FFFFFFFFh. The Number of blocks field is taken to be zero if the Block Descriptor is omitted from the Param-
eter List. If the Number of Blocks field contains zero, the capacity of the drive will not change, unless the maximum Number
of blocks change (due to changed Block Length, etc.) If the maximum Number of Blocks change, a zero in the Number of
Blocks field is processed as FFFFFFFFh. If the value in the Number of Blocks field is not greater than the maximum, the
drive will set its capacity to the value in the Number of Blocks field. A change in the Number of Blocks will not cause the
Format Corrupt condition.
Note. For drives with capacities over 5 Gbytes, the Density Code field byte is used for the Most Significant Byte (MSB) of
the Number of Blocks field.
The rest of the Mode Select parameters are organized into pages that group the parameters by function. The
parameter definitions are the same as those described in the Mode Sense command (Section 12.13) and are
not repeated here.
Each page of mode parameters begins with a two-byte Page Descriptor header. The Page Code identifies the
page of mode parameters that is being transferred (see Table 145). The Page Length indicates the number of
additional bytes of mode parameters contained in this page. The number of additional bytes sent must always
match the Page Length value.
The disc drive only verifies Mode Select data that is defined as changeable by the drive. The various disc
drives support the following page codes.
Note. See individual drive’s Product Manual, Volume 1, SCSI Interface commands supported section for
a table showing the mode pages that a particular drive implements. The table shows the default
parameters for pages that are implemented, and shows which mode parameters are changeable by
that drive model.
The detailed information can be obtained by issuing the Mode Sense command requesting changeable values.
Note. There may be implicit associations between parameters defined in the pages and block descriptors.
The block length affects the optimum values (the values that achieve best performance) for the sec-
tors per track, bytes per physical sector, track skew factor, and cylinder skew factor fields in the for-
mat parameters page. In this case, the drive may change parameters not explicitly sent with the
Mode Select command. A subsequent Mode Sense command would provide information on these
changes.
Table 140: Mode Select page descriptor header
Bit
Byte
76543210
0 0 0 Page Code
1
Page Length
2–n
Mode Parameters
139
139