You can specify the point at which the Fileshare Server displays a warning when the drive containing the log file is becoming full using the /p option:
fs /d dbase.ref /l logfilename /p nnn
where nnn specifies the percentage disk space remaining, below which the Fileshare Server displays a warning message. The default value is 5, that is, the Fileshare Server displays the warning message when the drive containing the log file contains less than 5% free space.