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Apparatus and method for distorted track data recovery by rewinding and re-reading the tape at a slower than nominal speed
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Inventors: Kauffman, Gerald C.; Hughes, Timothy C.; Heins, Don; Slovacek, Patricia; Abou-Jaoude, Fadi;
Assignee: Exabyte Corporation (Boulder, CO)
Primary Examiner: Young; W. R.
Assistant Examiner: Habermehl; James L.
Attorney, Agent or Firm: Nixon & Vanderhye
A helical drive system (10) reads tracks (18) on a storage medium (12), including tracks which appear as distorted tracks. Each track (18) comprises a plurality of blocks of data, with each block having unique block-identifying information. A read head (16C) traverses predetermined original azimuthal paths (P0) across the storage medium (12) for reading the blocks recorded along each of the original azimuthal paths (P0). A controller (50) uses the block-identifying information to determine whether any blocks expected to be read during the traversal of the original azimuthal paths (P0) were not read. If expected blocks were not read, the controller (50) rewinds or otherwise reverses the direction of travel of the storage medium (12); sends a signal to a tape transport drive (81) to slow the speed of the medium (12); and, directs that the medium (12) be re-read at a slower tape reread speed. During the slow re-read attempt, the read head (16C) traverses modified azimuthal paths (P1, P2, P3 , . . . P10) which are separated from one another by a distance less than the track pitch, thereby providing opportunities to read blocks which would not otherwise be read due to distortion of the tracks (18). |
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DETAILED DESCRIPTION OF THE DRAWINGS A helical-scan drive system 10 for recording on and reading magnetic tape 12 is illustrated in FIGS.
1 and 2.
A drum 14 is angularly oriented with respect to the edges and direction of travel 15 of magnetic tape 12.
As indicated in FIG.
2, drum 14 has heads 16A, 16B, and 16C mounted thereon to establish a physical relation between the heads on the drum 14 and the tape 12.
Head 16A is a write (or recording head); head 16B is a servo head; and, head 16C is a read (or playback) head.
The servo head 16B is pictured in the illustrated embodiment in view of its common use in helical-scan drive systems.
However, the servo head 16B is not employed in the data recovery method of the present invention.
By the illustrated arrangement, data is recorded on the tape 12 at an angle with respect to the direction of travel 15 of the tape 12, and hence, as indicated in FIG.
1, is recorded as discrete tracks or stripes 18 when the drum is rotated at a high speed relative to the speed of the tape 12.
As indicated in FIG.
2, the tape is preferably moved at a predetermined nominal rate (for example, 10.
89 millimeters per second in one embodiment) while the drum is rotated (for example, at 1800 rpm in one embodiment).
The tape speed is controlled by the rotational speed of capstan 19.
It is to be realized, however, that the operating speeds as set forth are by way of example and the invention is not meant to be limited thereto.
FIG.
3 shows a plurality of discrete tracks 18.
sub.
1, 18.
sub.
2, 18.
sub.
3, and 18.
sub.
4 properly recorded on tape 15 according to one embodiment of the invention.
Being properly recorded, each of the tracks 18 extends in a straight line for a predetermined length (depicted by line 22) at an angle 24 (also known as a "track angle" or "stripe angle") relative to the direction of tape travel (indicated by arrow 15).
The centerlines of adjacent tracks are separated by a track pitch, represented by reference numeral 26 in FIG.
3.
In the illustrated embodiment, the tracks are separated by inter-track guard bands 28
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