Hewlett-Packard Company

Mark E Mills

John L Moore

Kenneth G Richardson

Mark E Nash

Erik R Habbinga

Stephen G Uhlmann

Mark Millican

Frame-based heroic data recovery on data retrieved from mass storage in which identifiable blocks have been detected to be corrupt. Logical sets of blocks are configured into frames. The invention becomes operable when standard data recovery techniques such as Error Correction Code (&ldquo;ECC&rdquo;), working on a frame-by-frame basis, are unable to recover all the corrupt data within the frame because there are just too many corrupt data blocks. The invention then sequentially applies a preselected series of heroic techniques, each heroic technique in the series applied concurrently to all blocks in the frame. The invention combines the corrective effects of the individual applications of heroic techniques in the series, until sufficient individual data blocks overall in the frame are recovered to allow standard frame-based recovery techniques such as ECC to complete the job.

Frame-based heroic data recovery

An improved heroic data recovery technique in which the inventive mechanism initially calibrates data storage devices' read/write mechanism misalignment characteristics and then reduces such calibration to an off-track positioning table. The table reflects a histogram indicating statistically where the misalignment is most likely to be found based on measurement of the characteristics of the device. The device's off-track positioning mechanism uses this table to execute a series of off-track read attempts in statistical order of likelihood of recovering unreadable data. The read head moves first to the off-track position in the table where statistically the misalignment is most likely to be found, and then to the next most likely, and so on, until the data is either found and recovered, or the series embodied in the table is exhausted. If the table becomes exhausted, an alternative heroic technique must be applied.

Retry off-track positioning table

A method for reliably measuring preformatted servo patterns, on a magnetic tape, for positioning a magnetic head. The tape has constant frequency stripes marking servo pattern areas. The drive reading the preformatted tape has a read channel amplifier with automatic gain control (AGC). When a stripe is detected, AGC is enabled. Before leaving a stripe, AGC is placed on hold. The amplitudes of two servo bursts are then measured with a gain that has been calibrated by a signal from a stripe. During the time AGC is enabled, the amplifier peak output is limited to less than half the maximum amplifier peak output. The servo pattern signal amplitude is about twice the signal amplitude of a stripe, so that servo patterns are measured with almost the maximum signal-to-noise ratio. When a stripe is detected, a counter counts pulses resulting from the stripe signal, for a fixed time, to ensure that the stripe detection is valid. If the stripe is qualified, the servo pattern measurements are used for head alignment adjustment. If the strip is not qualified, the servo pattern measurements are discarded.

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Loveland, CO, United States of America

Mark E Mills