The erase of a tape is a write of a tape, just as every write.
Tapes are certifyed for a number of reads, a number of writes and a timeframe.
In DP there are (fairly save) defaults for these numbers and DP records them. Once these numbers are reached, the media is marked as 'poor' and not used for writing anymore. A format of the tapes can reset this...
DP also has tresholds for these numbers and once one of the tresholds is reached (number of months for example) the tape is marked as 'fair'. With normal and fair tapes in a robot, DP first uses the normal tapes, before fair tapes are used for writing.
Hence, reuse is possible. erase is not an option for most tapes (and other media) however, you can always write new data over the old. Formatting a tape in DP is writing a header on it. For tape wear, this counts as a write.
Erasing a tape for data security can best be done by writing random data to tape, best several times, just as disks are cleared. In the end, you can always remove the tape from the cartridge and run it trough a paper schredder.
Comes to mind, about 20 jears ago, I was a student on a trip to a large data-center. They needed to securely erase some tapes. We ended up bowling with tape-reels ;-)
