The ReqSenseLen field indicates the size of the SenseData buffer available. If the target indicates a SCSI status of CHECK_CONDITION then the ADD driver should issue a SCSI Request_Sense command with a data transfer length indicate by ReqSenseLen.
Note: ADD drivers are required to obtain Sense Data whether or not a Status Block is present. In the absence of a StatusBlock, this would usually be done using internal storage of the ADD driver.
However, if a status block is present, then the ADD driver must transfer no less than the number of bytes indicated by the ReqSenseLen field and provide this data in the SenseData buffer.