Using Fast Space; Exception Handling; General - Tandberg Data SLR7-140 PROGRAMMER Manual

Tandberg Data

27.3. Using Fast Space

The FAST option enables the Drive to perform fast space
to any data or tapemark block on the tape. All SPACE
operations except Space over Sequential Filemarks and
Space over Sequential
algorithm if the command is issued with the FAST bit
set. For Space over Sequential Filemarks the FAST bit is
ignored. Instead of searching in serpentine mode through
every track set, the Drive will use information recorded
on the tape to move directly to the wanted position.
When this option is used, the Drive will still be able
to report detected tapemarks during the space blocks
operation. Unrecoverable blocks between the start and
end position will, however, most likely not be detected.
Using the FAST
significantly faster than if NORMAL SPACE is chosen. The
only case when FAST SPACE can be more time consuming is
the first time when a SPACE command is issued into an
area of the tape that has not been read or written since
insertion of the cartridge, and where the end position
is relatively close to the start position (on the same
track set).
Instead of selecting FAST or normal space operation on a
command to command basis, it is possible to have the
Drive always use the FAST space algorithm by means of an
option controlled by the MODE SELECT command. By doing
so, the system drivers will not have to be changed to
get the advantage of FAST spaces. See the Miscellaneous
Parameters Page of the MODE SELECT command for details.
The recorded help
space operations is transparent to the user and it does
not violate any of the tape standards.

27.4. Exception Handling

27.4.1.

General

See sections on
Deferred Errors and Error Conditions For Media Access
Commands.
When the SPACE
detected errors
Information Bytes will hold the difference between the
requested and the
spaced. Note, however,
tapemarks, the VADD bit is never set and the Information
Bytes are never valid. See the following sections for
details.
A CHECK CONDITION caused by early termination of any
SPACE command never results in a negative Information
Bytes (residual count) value.
27-3 Tandberg SLR Product Line SCSI Functional Specifications
Setmarks
option, all spaces
information needed
Error Conditions
command has started
will set the
actual number
that when
Space
will use the
will normally
to enable
For All Commands,
execution,
VADD bit and
of blocks/tapemarks
spacing sequential
FAST
be
FAST
all
the