ICI has extended the technique which certifies the performance of a Terabyte optical tape to include applications with direct-read-after-write verification. The tape quality is guaranteed as a statistical upper limit on the probability of uncorrectable errors. This applies when the optimum verification strategy is used. Different strategies have been modelled and compared. The optimum strategy in practice is to rewrite records in which 4 or more bytes per codeword are in error (out of 8 maximum for full error correction). In the tape which is 35 mm wide, at least 99% of defective regions over 1 mm diameter are eliminated. This reduces uncorrectable errors by up to 3 orders of magnitude, and adds typically 10 years to service life.
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