Quantum DLT 8000 Product Manual page 305

READ Command (08h) (continued)
Table 5–72 READ Command Descriptor Block — Field Descriptions (continued)
Field Name
Fixed
Filemark, End-of-Data, and End-of-Medium/Partition Handling
If the tape drive reads a Filemark, it returns a CHECK CONDITION status. Within the
sense data, the Filemark and Valid bits are set and the Sense Key field is set to NO
SENSE. The information fields contain the residue count. The Additional Sense Code
and Additional Sense Code Qualifier fields are set to FILEMARK DETECTED. Upon
termination, the medium is logically positioned after the Filemark.
If the drive detects End-of-Data (EOD) during a READ, the drive returns a CHECK
CONDITION status. Within the sense data, the Valid bit is set and the Sense Key field
is set to BLANK CHECK. The End-of-Medium (EOM) bit may be set if the drive
determines that the tape is positioned past the PSEN marker. The information fields
contain the residue count. The Additional Sense Code Qualifier fields are set. Upon
termination, the medium is physically positioned before EOD and after the last block on
tape.
Description
This bit specifies whether fixed-length or variable-length blocks are to
be transferred, and gives meaning to the Transfer Length field of the
READ command.
When set to 0, variable-block mode is requested. A single block is
transferred with the Transfer Length specifying the maximum
number of bytes the initiator has allocated for the returned data.
When the Fixed bit is set to 1, the Transfer Length specifies the
number of blocks to be transferred to the initiator. This is valid only if
the logical unit is currently operating in Fixed Block mode.
When the Transfer Length is 0, no data is transferred and the current
position on the logical unit does not change. This is not an error
condition.
A successful READ with Fixed bit set to 1 transfers (current block
length) x (# of blocks x block size) bytes of data to the host. Upon
termination of READ, the medium is logically positioned after the last
block of data transferred (EOM).
Note that a READ command in fixed mode with an odd block size
returns a CHECK CONDITION: the DLT 8000 tape drive does not
support odd block number transfers.
Quantum DLT 8000 Tape System
SCSI Commands
5-161