This folder can be used by a tape writing procedure to mark backup and freeze
archives as actually written to tape.

The marker format is a file USERID/ARCHIVE/onTape
where onTape only holds the actual date when tape writing completed.

As an example a user XYZ could have the marker XYZ/archive-JYiIVm/onTape
containing the time stamp
2020-09-30T15:51:17+0200
where the timezone offset is expected to match the local time zone.
