Massive plate to improve file performance
Original Publication Date: 2001-Sep-01
Included in the Prior Art Database: 2003-Jun-20
Disk drives increase capacity in part by increasing the track pitch of the drive. This increase in track pitch makes the drive more susceptible to being off track during a read or write operation. When sufficiently off track during a read, the data cannot be read. When off track during a write, the write is aborted to prevent either damaging data on an adjacent track, or writing the data where it cannot be read. These events are called "soft errors" because trying again after one revolution of the disk will result in success. Despite the ability to recover from them, soft data errors decrease the drive's performance since waiting a revolution is lost time. One particular source of off track motion is operational vibration, which is the shaking of the drive by external forces. This shaking is independent of track pitch, so as track pitch drops, the off track caused by operational vibration increases as a portion of track pitch, meaning that each generation of drives has to take greater measures to protect against it. There are a number of known solutions to this problem. One solution is to increase the servo bandwidth, or its ability to follow the motion of the disk. A disadvantage of this approach is that such a scheme puts more energy into the actuator, which can cause it to vibrate more at structural resonances. Increasing the servo bandwidth makes the mechanical design more stringent. This stringency is realized either in increased cost or increased inertia, which in turn reduces performance. Another solution is to reduce the head to pivot distance. In this way, rotational off track couples less into radial motion due to the shorter moment arm. But a shorter head to pivot distance reduces the area over the disk where data can be stored, which reduces the capacity of the design. Yet another solution is to mount the drive more rigidly in the first place. But this is the responsibility of the disk drive customer and not the designer. Further, this increases the customer's cost, and also prevents putting the current disk drive into legacy boxes. This article discloses an idea without any of these disadvantages: Add a metal plate onto the drive of such a size that the next larger form factor is not exceeded. For example a 3.5 inch drive, with a 1 inch z-height can add a plate about .6 inches in thickness onto the cover side without exceeding the next form factor of 1.6 inch z-height. Similarly, a 2.5 inch drive could add a plate that stays within a 3.5 inch form factor. (That is, the "plate" can have a hollow spot to hold the drive, while the overall size is still within the form factor of a 3.5 inch drive. This plate would substantially increase the mass of the disk drive proportionally reducing the amount of motion caused by a given rotational force. If all the drives in a box have this plate added, the effect will be greater, as the vibration force caused by the adjacent drives will be reduced as well.