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TAPE FORMATS
6.4.3 Data Area
The third area on this tape layout is the Data area, which is written as a sequence of groups beginning with a
special Vendor Group. Each group is a fixed size and stores uncompressed records, entities (DDS-DC fonnat
only), fIlemarks, and save-set marks written by the host. The variable-length records and fIlemarks are
mapped into the group by indexing.
6.4.4 End-of-Data (EOD) Area
The last area in this tape layout is the End-of-Data (EOD) area -- the point on the tape where the host ceased
writing data. This area is not specifically written through host command. Rather, the drive will detect any
conditions -- such as a REWIND following a WRITE command -- which comprise EOD and then generate
the EOD area.
The area is physically long enough to guarantee that it is detected during fast searching. A set of at least 12
Data area amble frames, which are continuous and contiguous with the last frame of the last data group
written precedes the EOD area.
In the case where existing data is partially overwritten and the overwrite ends before the existing EOD area,
a new EOD is generated at that point. A tape may, therefore, contain more than one EOD area. However, the
EOD closest to the BOT is the only valid one. Any data or other EOD areas beyond that point are logically
inaccessible.
6.5 Two-Partition Layout
The two-partition tape layout provides two separate areas that may be written independently to be contained
on a single tape volume. The host chooses the tape layout -- single data space or two-partition -- before it
sends data for writing to a blank tape for the first time or when it sends a tape fonnat command.
The two partitions are adjacent on the tape with no gap between them. The partition closer to the BaM is
Partition 1; the partition closer to the EOM is Partition O. The boundary between the partitions is defined by
an upper limit of the value of the Absolute Frame Count of Partition 1.
The two-partition layout is generally made up of:
o
The Device Area
o
Partition 1
o
Partition 0
The Device area is the same as the Device area for the single data space tape layout..Also, each partition is
made up of a Reference and System area, a Data area, and an EOD area. These areas are the same as for the
single data space tape layout. Additionally, Partition 1 contains a synthetic EaT and EOM; Partition 0
contains a synthetic BOT. Thus, each partition is structured identically to a single data space tape except for
the Device area.
6-7
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