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SCSI Commands
Space-by-Count Functions
Space to EOD
If the Code field is 001b, then the logical position is moved the number of file marks
indicated by the Count field. If BOT or EOD is detected before the requested logical
position, then the logical position is set to that position.
If the Code field is 011b, then the logical position is set to after the last valid block on
tape. In this case the count field is ignored.
Any other value of the Code field will cause Check Condition status to be returned.
Spacing to sequential file marks is not supported. Set marks are not supported. The
Sense Key is set to Illegal Request and the Additional Sense is set to Invalid field in
CDB (2400).
The Count field indicates both direction and number of blocks or filemarks to space
over from the current logical position. A positive value N in the Count field moves the
tape forward over N blocks or filemarks. A negative value -N (2's complement) in the
Count field moves the tape backward over N blocks or filemarks. Zero in the count
field causes no tape movement and is not considered an error.
When there are no exception conditions during space functions, forward tape motion
ends on the EOT side of the last block or filemark and reverse motion ends on the
BOT side of the last block or filemark.
•
If a filemark is encountered while spacing over blocks, a Check Condition Status
is returned. The Sense FM bit is set and the Sense Valid bit is set, indicating
Residual Length is non-zero.
The Residual Length equals the difference in the requested count and the actual
number of blocks spaced over not including the filemark. The tape is positioned
on the logical EOT side of the filemark if movement was forward or on the logical
BOT side of the filemark if movement was reverse.
•
If EOD is encountered while spacing forward, Check Condition is returned with
08h Sense Key. Extended Sense Valid bit is set, indicating Residual Length is
nonzero.
•
If BOT is encountered while spacing in reverse, Check Condition is returned with
40h Sense Key. Extended sense Valid bit is set, indicating a nonzero Residual
Length.
•
If EOT is encountered while spacing forward, Check Condition is returned with
40h or 43h Sense Key. Extended Sense Valid bit is set, indicating a nonzero
Residual Length.
•
If an unrecoverable data error is encountered, Check Condition is returned,
Extended Sense Key is set to Medium Error, and Extended Sense Valid bit is
set, indicating Residual Length is nonzero.
The Count field is ignored in the space-to-EOD function.
In the space-to-EOD function, the tape is positioned such that a subsequent WRITE
command appends data to the last recorded information on the tape. This positioning
is done at high search speed.
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