Chapter 4: SCSI Commands
4-116
July 2004
81-81276-01 Rev A01
When executing SPACE, the tape drive implements the following hierarchy:
•
Blocks – lowest
•
Filemarks
•
EOD
•
BOM/P or EOM/P – highest.
Therefore, SPACE N Blocks halts with GOOD status after the Nth block or with CHECK
CONDITION status on any occurrence of Filemark, EOD, BOM/P, or EOM/P. SPACE N Filemarks
halts on the Nth Filemark or on any occurrence of EOD, BOM/P, or EOM/P, etc.
Depending on the size of blocks, read-ahead data in the buffer allows some spacing requests to be
satisfied without medium movement.
4.23 TEST UNIT READY (00h)
The TEST UNIT READY command checks if the tape drive is ready for commands involving medium
movement. If the tape drive has a data cartridge loaded, the command returns a GOOD status.
Otherwise, it reports CHECK CONDITION.
Count
When spacing over blocks or marks, the Count field is interpreted as follows:
•
A positive value N causes forward movement over N blocks or marks. The
tape drive logically positions the medium after the Nth block or mark on the
EOM/P side.
•
A 0 value causes no change in the logical position.
•
A negative value -N (two’s complement notation) causes reverse movement
over N blocks or marks. The tape drive logically positions the medium on the
BOM/P side of the Nth block or mark.
•
When spacing to EOD, the Count field is ignored. Forward movement occurs
until the tape drive encounters EOD. The position is such that a subsequent
WRITE command would append data after the last object that has been written
to medium before EOD.
Table 4-68.
SPACE (11h) Command Descriptor Block — Field Descriptions
(Continued)
Field Name
Description
Содержание DLT1/VS80 SCSI
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