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6.Command Specification READ
6-66 SONY AIT-3Ex drive SDX-800V series Ver.1.1
The meaning of EOM is different for READ than for a WRITE type of command. EOM is only reported when the
physical EOM/P is encountered. The drive returns a CHECK CONDITION status. The EOM and Valid bits are set
and the Information fields contain the residue count. If EOD is not written after the physical EOM/P, the Sense Key
is set to MEDIUM ERROR and the Additional Sense Code and Additional Sense Code Qualifier fields are set to
EOM/P Detected. If EOD is written, the Sense Key is set to BLANK CHECK and the Additional Sense Code and
Additional Sense Code Qualifier fields are set to END-OF-DATA DETECTED. The tape is physically positioned at
EOM/P.
For a File-mark, a (reported) Save-Set Mark, EOD or EOM detected, if the Fixed bit is set, the Information field in the
REQUEST SENSE Data will be set to the difference (residue) between the requested Transfer Length and the actual
number of blocks read (not including the File-mark or Save-Set Mark). If the Fixed bit is set to ZERO, the information
bytes will be set the requested Transfer Length because File-marks and Save-Set Marks are considered to have a
byte count of ZERO, (though this does not cause the ILI bit to be set).
READ may return the following sense keys on a CHECK CONDITION:
NO SENSE: If the actual Block Length is different from the specified Transfer Length and the SILI bit is ZERO, the ILI
(Incorrect Length Indicator) bit and Valid bit are set to one. The Information bytes in extended sense are set to the
difference (residue) between the requested Transfer Length and the actual Block Length, or in Fixed Block mode,
the difference (residue) between the requested number of blocks and the actual number of blocks read (not including
the incorrect length block). No more than Transfer Length bytes are transferred to the initiator and the tape is
logically positioned after the block (EOM side).
If the drive reads a File-mark during this command, it sets the File-mark bit in the REQUEST SENSE data. Upon
termination, the tape is logically positioned after the File-mark (EOM side). If, however, the drive encounters a
Save-Set Mark during this command, nothing is reported unless the SDX-800V has been configured through
MODE SELECT to Report Save Set Marks. If the Report Save Set Marks configuration is enabled then the Valid bit
and the Additional Sense Key flags are set in the REQUEST SENSE data to indicate that a Save-Set Mark has been
encountered. The tape is also logically positioned after the Save-Set Mark (EOM side).
For both a File-mark and a reported Save-Set Mark, if the Fixed bit is one, the Information bytes in the REQUEST
SENSE data are set to the difference residue between the requested Transfer Length and the actual number of
blocks read (not including the File-mark or Save-Set Mark).
If the Fixed bit is set to ZERO, the Information bytes are set to the difference (residue) between the requested
Transfer Length and the actual number of bytes read. File-marks and Save-Set Marks are considered to have a byte
count of ZERO, though this does not cause the ILI bit to be set.
MEDIUM ERROR: The current block being read or a previously acknowledged WRITE type of operation
experienced an error probably related to the condition of the tape.
HARDWARE ERROR: Either a previously acknowledged WRITE type of operation had a major non-media related
failure or the read itself experienced the failure. The Valid bit is set, and the Information field contains the appropriate
residue. The meaning of EOM is different in a READ command from that in a WRITE type of command. EOM is only
reported on physical end-of-media. However, this condition is indistinguishable from other fatal servo errors and so
is reported as a HARDWARE ERROR.
BLANK CHECK: If EOD (End-of-Data) was encountered during a read, the sense key is BLANK CHECK, the Valid
bit is set and the Information bytes contain the residue count.