Tandberg Data SLR7-140 PROGRAMMER, Руководство пользователя

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Tandberg Data About Tape Streamers
2-15 Tandberg SLR Product Line SCSI Functional Specifications
After writing data from BOP on a partition, the medium
is considered to be a contiguous grouping of blocks,
filemarks, setmarks and gaps. Certain ANSI standards
define gap lengths which, if exceeded, are to be con-
sidered as having reached blank medium. Depending on the
tape format, this blank medium may be treated as an end-
of-data indication or an unrecoverable medium error
causing an interchange error. Unrecorded volumes (new or
erased) may exhibit blank medium characteristics if an
attempt is made to read or space the volume before data
have been written.
2.5. Overwrite
Normally tape streamers do not allow update of data
already written on a volume. The structure and layout of
the physical elements on the Recording-Area are such
that they do not facilitate writing over old data with
new data in the middle of a partition. When writing new
data on a volume there are only two possibilities:
„
A write operation may be started from BOP. All
existing data on that partition will be destroyed.
This is true even if the new write operation writes
less data than the amount of data already on the
partition. The data “ left” on the partition can not
be recovered.
„
A write operation may append data to existing data on
a partition. In this case the medium must be
positioned at end-of-data (EOD) before the write
operation is started. The medium may be positioned at
EOD by reading or spacing until the Drive indicates
EOD. It is also possible to position the medium to
EOD by executing a SPACE command with a Space Code of
3 (Space to EOD).
If the current tape position is not at BOP or EOD, a
write operation will be terminated immediately with
CHECK CONDITION status and the Error Code is set to W
RITE
A
PPEND
E
RROR
(Write After Read).
However, in addition to the two possibilities mentioned
above, the Tandberg SLR Product Line Tape Drives offer
under certain conditions the following two overwrite
capabilities:
„
The data following the very first data block in a
partition may be written over (leaving the first data
block intact). The following restrictions do however
apply:
1) The medium must be positioned after the 1st
logical block in partition 0.
2) The length of this block must be less than 65536
(10000h) bytes when using a SLRtape140 to SLRtape7
or SLR32, medium or less than 32768 (8000h) bytes
when using an SLR5 or DC9250 medium.
3) There must be no tapemarks either immediately in
front of or immediately after the 1st data block.