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298 Fibre Channel Interface Manual, Rev. D
12.38 Request Sense command
The Request Sense command requests that the disc drive transfer sense data to the initiator in the format
shown in Table 202. The sense data is valid after a Check Condition status returned on the prior command.
Sense data is returned in the Fibre Channel Protocol Response frame with the Check Condition bypassing the
need for the Request Sense command. Sense data must be cleared upon execution of any subsequent com-
mand. For Fibre Channel, data returned in response to a Request Sense command is only valid if commands
are not queued in the drive.
If a disc drive sends a Check Condition status as a response to a Request Sense command being in error, it
will do so only if the error was a fatal error. For example:
1. The disc drive receives a nonzero reserved bit in the command descriptor block.
2. A disc drive malfunction prevents return of sense data.
If any nonfatal error occurs during execution of Request Sense, the disc drive returns sense data with Good
status. Following a fatal error on a Request Sense command, sense data may be invalid.
The disc drive terminates the data when the number of bytes indicated in the Allocation Length field have been
transferred or when all available sense data have been transferred to the initiator, whichever is less. The disc
drive always returns sense data in the extended sense data format shown in Section 11.5.1.
Field definitions (listed alphabetically)
Allocation Length
The allocation length in byte four of the format shown specifies the number of bytes the initiator has allocated for returned
sense data. The allocation length should always be at least 18 bytes for disc drive devices for the initiator to receive all of
the disc drive sense data. Any other value indicates the maximum number of bytes that will be transferred.
Control
See Control Bytes in Section 11.2.1.6.
Table 202: Request Sense command (03h)
Bit
Byte
76543210
000000011
100000000
Reserved
200000000
300000000
4
Allocation Length (in bytes)
5
Control
03h
Table
number
202
202