Chapter 4: SCSI Commands
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July 2004
81-81276-01 Rev A01
Fixed
The fixed bit specifies both the meaning of the Transfer Length field and whether
fixed-length or variable-length blocks are to be transferred. Setting the Fixed bit to
0 selects Variable Block mode. A single block is transferred from the initiator and
is written to the logical unit beginning at the current logical medium position.
Upon successful termination, the medium is logically positioned after this block
(EOM/P side). The Transfer Length specifies the number of bytes that the tape
drive handshakes out from the initiator.
Setting the Fixed bit to 1 causes the Transfer Length field to specify the number of
blocks to be transferred to the host beginning at the current medium position. This
form of WRITE is valid only if the logical unit is currently operating in Fixed
Block mode, in other words, when it has been instructed to use fixed-length blocks
with MODE SELECT. The current block length is the block length defined in the
MODE SELECT command. Upon termination, the medium is logically positioned
after these blocks.
Transfer Length
This field contains the length of the data transfer in bytes or blocks, depending on
whether Fixed or Variable block mode is selected.
When the Transfer Length is 0, no data is transferred and the current position on
the logical unit is not changed.
Exception Conditions
If EOT is detected while writing, the tape drive finishes writing any buffered data.
The command terminates with CHECK CONDITION status. Within the Sense
data, the EOM bit is set, the Sense Key field is NO SENSE, and the Additional
Sense Code and Additional Sense Code Qualifier fields are EOM/P Detected. The
tape drive attempts to complete any subsequent writes, returning a CHECK
CONDITION status in each case.
If the tape drive encounters the physical EOM when attempting to write, it returns
CHECK CONDITION status. Within the Sense data, the EOM and Valid bits are
set and the Sense Key field is Volume Overflow. The Information fields contain
the residue count and the Additional Sense Code and Additional Sense Code
Qualifier fields are EOM/P Detected. The medium is physically positioned at
EOM/P.
Table 4-70.
WRITE (0Ah) Command Descriptor Block — Field Descriptions
(Continued)
Field Name
Description
Содержание DLT1/VS80 SCSI
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