Space-By-Count Functions - Quantum LTO 2 User Manual

Space-By-Count
Functions
LTO-2 SCSI Interface Guide
If the Code field is 001b, then the logical position is moved the number of
filemarks 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 filemarks 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
2
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.
Chapter 2 SCSI Commands
SPACE Command
262