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SCSI Commands
Read Command Operation
End-of-Data
Filemark
Transfer Length Satisfied
long and Check Condition status. If a block that is shorter than the configured length
is encountered before the sequence is complete, the blocks up to that block are
returned followed by all of that block and Check Condition status. The current
position is set after the last block that was returned or partially returned.
If the Transfer Length field is zero and the Suppress Illegal Length Indicator and the
Fixed bit are not both set, then no action is taken.
If Suppress Illegal Length Indicator (SILI) flag is set and the Fixed bit is set, then
Check Condition status is returned. The sense key is set to Illegal Request and the
Additional Sense to Invalid Field in CDB (2400).
The Read command is complete when one of the following conditions is met. These
conditions are described in the following paragraphs.
•
End-of-Data (EOD) is reached.
•
A filemark (FM) is read.
•
Transfer length is satisfied
•
End-of-Tape (EOT) or end-of-partition (EOP) is reached.
•
Unrecoverable data error occurs.
•
Detection of incorrect block length.
If EOD is encountered, the command terminates with a Check Condition status and a
Sense Key of 08h. If the Valid bit (byte 0, bit 7) is set indicating a residual count, the
Residual length field is determined as follows:
•
If the Fixed bit is 1, it equals the difference between the CDB transfer length and
the number of actual blocks read.
•
If the Fixed bit is 0, it equals the CDB transfer length.
The tape is then positioned to allow an Append Data operation.
If a filemark is encountered, the command terminates with a Check Condition, and
the filemark bit (byte 2, bit 7) of the sense data is set to 1. If the Valid bit (byte 0, bit
7) is set indicating a residual count, the Residual length field is determined as
follows:
•
If the Fixed bit is 1, it equals the difference between the CDB transfer length and
the number of actual blocks read.
•
If the Fixed bit is 0, it equals the CDB transfer length.
On termination, the tape is positioned after the filemark on the EOT side of tape.
If the CDB Transfer Length is satisfied, the command completes successfully with a
Good Status, and the tape is positioned on the EOT side of the last block read.
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