The drive mechanism and media tolerances must therefore be tightly controlled to maintain a very precise alignment between the path of the head and the data tracks written on the tape. As previously mentioned, this particular architecture suffers from a number of inherent weaknesses that negatively impact reliability, performance and cost. Whenever the flow of data is interrupted, the drive must stop the tape, back it up, accelerate it to the appropriate speed, and then continue the data transfer in the same orientation as before. Degraded Reliability Backhitching. Backhitching also seriously impacts data reliability because changes in tape direction cause high transient forces which accelerate wear on the media and decrease mechanism life.
Worn tapes increase the rate of head wear and are a source of debris and contamination.
These factors all ultimately impact the reliability of data on the tape and decrease the useful life of the media and tape drives. The performance of streaming tape devices depends on the geometry of the recorded tracks, i.e., the straightness of the tracks, the alignment between the track and the edge of the tape, and the horizontal position of the track with respect to the edge of the tape. There are many factors that contribute to changes in track geometry - in normal storage environments, tracks tilt and bend due to temperature, humidity, tape wear, drive tension variations and accumulated debris. In addition to changes in track geometry, differences in drive mechanisms can affect the ability of one drive to read a tape written by another. Through use and over time, the alignment of heads in the tape drive can drift, further decreasing confidence in the long-term reliability of data availability and interchangeability.