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The graph called "Slope and amplitude of edge bumps" on this page shows the standard deviations for the amplitudes, or heights, of the irregularities in our eight test tapes. A larger number indicates both a greater frequency as well as a greater size of the jagged edges. This graph also shows the standard deviation for the slope of the bumps. A small standard deviation indicates that they are gentle; a larger number indicates a steeper slope. Notice that the two graphs match fairly closely with respect to LTO media manufacturer. Tapes that had a higher frequency of edges--and more that were jagged--also tended to have steeper bumps.
As mentioned earlier--and with respect to this single aspect of tape quality--the highest quality tapes were those that didn't have too many bumps, and those that did exist were fairly small. Also, the slope of those bumps was not too steep. Do these results suggest that you should only purchase tapes from TDK because one of its tapes showed the lowest amplitudes or that you should purchase tapes only from Fuji because one of its tapes showed the best slopes? Not necessarily.
Remember, we only examined one indicator of tape quality--the tape edge--and our test sample was small. A different test, or perhaps the same test repeated with different tape samples, may produce vastly different results. But in the absence of any other data or any other means of testing edge distortions,
In addition to the tests described, we also looked at many other tape edges and made an unexpected discovery: All the tape edges had the most damage at the beginning and the end of a tape. This was surprising because we had originally associated tape edge quality only with the slitting process, at least as far as new tapes were concerned. Because slitting is done on large rolls of tape--before the tape is cut into the cartridge size length (about 600 meters)--why would the opposite ends of the tape show more edge damage than the middle?
We concluded that this damage was caused by the equipment that spools the tape out onto the cartridge hub. This equipment attaches the end of the tape to the hub, and it also adds a leader to the beginning of tape. In all likelihood, it's this process that's causing further harm to the tape edge. Not all tapes showed the same amount of damage, but all suffered some damage. We think that there's room for improvement in this area.
Obviously, more conclusive testing would require a larger sample size, which would also produce higher quality test results. For instance, we only tested two samples of tape from each LTO tape vendor. The edge quality may fluctuate with changes in the manufacturing slitting process, so tests should be done on an ongoing basis.
Furthermore, we only ran tests on new tapes out of the box. Are the LTO drives really "tape-edge eaters," as has been rumored? To determine if there's any truth to that statement, we would need to test a new tape, run it in an LTO drive and then retest it after 1,000/5,000/10,000 passes to see if its edge further deteriorates. Finally, we tested only LTO tapes, but the same or similar tests could be done for other tape technologies as well.
Testing tape quality isn't easy, but it certainly can be done. Because a considerable proportion of a budget is regularly spent on purchasing LTO tapes, investing some resources to discover the quality of LTO tape would be money well spent. We believe that anyone who purchases tapes in quantities should seriously consider setting up a program that periodically tests not just the tape edge quality, but also tests other tape quality parameters such as the integrity of the servo track, the number of media defects and the mechanical components of the cartridge.
This was first published in March 2004