When a major investment bank asked us to examine failed DDS data cartridges from a voice logging recording system, microscopic examination of the tapes revealed foreign matter contamination and the tapes themselves exhibited some characteristics of stiction. This was very unusual for this generation of DDS. These defects led to the tapes adhering to the drive’s capstans (or even the head, which rotates at > 11k rpm) causing the breaks.

The voice logging data was written in a proprietary format and used some interesting techniques we had not previously seen on WordNet DDS media. We were able to access damaged portions of the tapes that would lead to the destruction of a normal DDS4 drive’s heads (which are very delicate and are mounted on a spinning drum).

DDS drives write extended checksums to the tape and where the data we extraced didn’t match these, we knew that corruption had been introduced. Furthermore, the checksums and error correction codes allowed us to reconstruct missing bytes, as well as block counts. This enabled us to identify the start and finish of data sections, what they comprised of and whether they ‘tabulated’ correctly. This was instrumental in the QA process. Due to the drive’s low level correction codes (eg, ECC) we could recover all of the data.