Oracle Secure Backup Installation And Configuration Manual page 166

write window close time
the volume set until it expires (as determined by its expiration policy), or until it is
relabeled, reused, unlabeled, or forcibly overwritten.
A write window is associated with a family. All volume sets that are members
media
of the media family remain open for updates for the same time period.
write window close time
The date and time that a volume set closes for updates. Oracle Secure Backup
computes this time when it writes backup image file number 1 to the first volume in
the set. If a volume set has a write window close time, then this information is located
in the volume section of the
volume label.
write window time
The length of time during which writing to a volume set is permitted.
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