HGST Ultrastar 7K4000 (SAS) Hard Disk Drive Specification
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18.10 MODE SENSE (1A)
Table 96: Mode Sense (1A)
The MODE SENSE (1A) command provides a means for the drive to report various device parameters to the Initiator. It is the
complement to the MODE SELECT command.
If the DBD (Disable Block Descriptor) bit is zero, the Target will return a Block Descriptor. If the DBD bit is set to 1, the Tar-
get will not return a Block Descriptor.
Allocation Length indicates the maximum number of bytes that the Initiator has set aside for the DATA IN phase. A value of
zero is not considered an error. If the allocation length is smaller than the amount available, that portion of the data up to the
allocation length will be sent. This may result in only a portion of a multi-byte field being sent.
Page Control Field: PCF (Page Control Field) defines the type of Page Parameter values to be returned.
PCF Meaning
0 0 Report current values. The drive returns the current values under which the logical unit is presently configured for
the page code specified. The current values returned are
1. Initially following power-up but before the media is accessed, the default values become current. Once the media
can be accessed, the saved values are read from the Reserved Area and become current.
2.The parameters set in the last successful MODE SELECT command.
3.The saved values if a MODE SELECT command has not been executed since the last power-on, hard RESET con-
dition, or TARGET RESET message.
Following the completion of start-up, execution of the MODE SELECT command can modify the current values.
Note: Those parameters associated with format are not considered current and are not saved until the successful com-
pletion of a FORMAT UNIT command.
In addition, the current values take on the saved values after a reset if the parameters were saved. If the Page Code is
3Fh, then all pages implemented by the Target are returned to the Initiator with fields and bit values set to current val-
ues.
If the Page Code is not 3Fh, the page defined by the Page Code, if supported by the Target, is returned with fields and
bits set to current values.
Note: The drive will not process the MODE SELECT command until the completion of spin-up. Therefore, the Initi-
ator cannot modify the current values prior to the saved values being read in.
0 1 Report changeable value. The drive returns the changeable values for the page code specified. The page requested is
returned containing information that indicates which fields are changeable. All bits of parameters that are changeable
shall be set to one. Parameters that are defined by the drive shall be set to zero. If any part of a field is changeable, all
bits in that field shall be set to one.
Note: For a value field such as the buffer ratios of page 2 the bit field will not indicate the range of supported values
but rather that the field is supported.
Byte
Bit
76543210
0 Command Code = 1Ah
1 Reserved= 0 RSVD DBD Reserved = 0
2 PCF Page Code
3 Subpage Code
4 Allocation Length
5 VU = 0 Reserved = 0 FLAG LINK
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