Shoe-Shining Effect
Tape Data Recovery - Shoe-Shining Effect
Shoe-shining effect is a condition which occurs when the data transfer rate to a magnetic tape falls below the minimum capacity at which the tape drive heads are designed to transfer data to a running tape.
The shoe-shining effect significantly affects the attainable data rate. This is not desirable in data backup processes. Shoe-shining effect also creates undue stress on the drive mechanism and the tape medium itself, resulting in hardware failure.
To overcome this effect, the tape drive must, at first, decelerate the tape, and then stop it, rewind back a little, and accelerate it to an appropriate speed and continue the process from the earlier position.
This action, however, was not possible in earlier tape drives that had large tape spools. The higher inertia of the larger spools prevented them from starting and stopping easily. To overcome this, several feet of loose tape were played out and pulled by a suction fan down into two deep open channels on either side of the tape head and capstans. These long thin loops had far less inertia than the two reels and could be repositioned rapidly.
Later, most of the tape drive models were provided with internal data buffer to reduce start-stop situations. In these models, the tape was stopped only when the buffer is empty with no data to be written or when it was full of data during reading.
The latest models do not operate at single fixed linear speed; rather, they have a few speed levels. They feature an algorithm that dynamically matches the tape speed level to computer’s data rate.
