In a data storage subsystem, drive-level processing treats data storage
media as WORM by automatically advancing a write append limiter as data is
written, and preventing changes to data occurring before the write append
limiter. Despite this media's WORM nature, the drive-level processing
permits limited overwriting of data at the end of tape since the write
append limiter lags the current write location by the margin of a write
allowance index. Thus, despite the drive's treatment of the media as WORM,
the drive permits overwriting of trailing metadata in order to facilitate
write append operations.
