I appreciate the numerous references to migrating data tapes every 5 years or so. However, that should not be misinterpreted to mean simple physical migration but should include a change of file format if warranted.
As for the physical make-up of data tape I'm not sure. I do know that DV-CAM, R-DAT and other like miniature digital tape types are manufactured using evaporated metal. This method yields the most unstable tapes and should be used only for production and storage in the 3 - 5 year time frame only. I personally have seen tapes of both formats generate huge error counts after only a couple years.