Eod Area; Early Warning Point (Ewp); Initialization - Seagate STD124000N Product Manual

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3. Amble frames between Frame A and Frame B should have a value of group
number that is equal to that of Frame A. Other frames between Frame A and
Frame B should have a value of group number that is greater than that of
Frame A.
4. There should be a minimum of 29 frames between Frames B and C. For
example, if Frame B has an AFN of n + 2 ≤ n' ≤ n + 12 , then Frame C should
have an AFN of n' + 30 minimum. No unrecorded space, physical discontinuity
or seam or AFN discontinuity or repetition is allowed between Frames B and C.

EOD Area

The data area is always followed by an EOD area . More than one EOD area can
exist on tape, but the EOD area closest to LBOT is the only valid one for information
interchange. The EOD area is also followed by a post-EOD area that extends to the
physical end of tape (PEOT).

Early Warning Point (EWP)

The early warning point (EWP) functions as an alert from the DDS-3 drive to the
host that the PEOT is being approached. Any data transfer operation currently
underway should be completed, the data should be recorded to tape and no more
data transfers occur until a new cartridge is loaded.
In the case of a new or unwritten tape, the EWP is calculated by the drive based on
a number of factors including tape cartridge type (which automatically renders a
media length factor) and is then held in memory. By specification, the EWP is
always a minimum of 3 mm before the PEOT. If data is recorded beyond the
calculated EWP, the after early warning point (AWEP) bit is set on the last basic
group completely or partially recorded before that point. The AWEP now denotes
the position of the EWP the next time that the tape is read. In addition, this
information is also recorded into the system log as part of the update of the tape
history before unloading the tape.
For a tape that contains data, but which is being overwritten, the drive follows the
same procedure as with a new or unwritten tape. The drive calculates the EWP,
ensuring that the calculated EWP is not less than 3 mm before the PEOT. If data is
written beyond the EWP, the AWEP bit is set on the last basic group completely or
partially recorded before that point. The AEWP now represents the position of the
EWP for the next read. The system log is also updated at unload time to reflect this.

Initialization

Initialization refers to the process of preparing the tape for recording user data for
the first time. The reference area, system area and the vendor group are all
recorded per DDS-3 standard requirements in preparation for recording of the first
recorded data group to tape.
Performing the Initialization step on a previously recorded tape effectively destroys
all data contained on the tape, including that found in the reference area, system
area and in the vendor group.
Chapter 6
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