Key Code Qualifier

"KCQ redirects here. For the radio station in Saginaw, Michigan, see WKCQ"

Key Code Qualifier is a computer term used to describe an error-code returned by a SCSI device.

When a SCSI target device returns a check condition in response to a command, the initiator usually then issues a SCSI Request Sense command. This process is part of a SCSI protocol called Contingent Allegiance Condition. The target will respond to the Request Sense command with a set of SCSI sense data which includes three fields giving increasing levels of detail about the error:
*K - sense key - 4 bits
*C - additional sense code (ASC) - 8 bits
*Q - additional sense code qualifier (ASCQ) - 8 bitsThe initiator can take action based on just the K field which indicates if the error is minor or major. However all three fields are usually logically combined into a 20 bit field called Key Code Qualifier or KCQ. The specification for the target device will define the list of possible KCQ values. In practice there are many KCQ values which are common between different SCSI device types and different SCSI device vendors.

List of common SCSI KCQs

References

[ftp://ftp.t10.org/t10/drafts/spc4/ SPC-4] clause 4.5.6 and annex D.2