Never
Never format a track. If a disk I/O
error occurs, BackupST is aborted with an error
message.
Always
Format every track before trying to write on
the track. After formatting of the track the
behavior of BackupST is as if format On
error was selected.
On error
Format a track if an I/O error occurs.
After formatting of this track, writing to the
track is tried again. Up to 5 retries will
take place. If the retries have no effect,
BackupST is aborted.
When every track needs reformatting, it turns
out to be a time consuming proces. If more
than 3 tracks need formatting on a particular
side of a disk the remaining tracks on that
side will be formatted before trying to write
on that side.