Control service allows you to know reliability of your backup or archive tapes.
Check your tape media regulary, secure you to restore your data after disaster.
Control process is a physical reading of the support, byte by byte without translation to preserve confidentiality.
A log file store control attribute, bytes, blocks, tape-marks count and blocks detected with read corrections or read errors. With these informations, you can determine a management strategy of your tape, storage as it is, regeneration or add new copy.
Control allows you verify compatibility of your media with other one drive, than the one it wrote.