International Business Machines Corporation

Colleen Renee Stouffer

Alex Chliwnyj

Karl Allen Nielsen

Steven Carter Wills

Kenneth Wayne Todd

Lee Jason Sanders

Matthew John Fairhurst

David Frank Mannenbach

Kevin Keith Kartchner

Ronald K Rhodes

Method, system and computer program product are provided to improve the reliability of data transfers from RAID systems. Although some read errors may be detected by the RAID controller, other errors may not be; undetected errors may affect the integrity of the data. In accordance with the present invention, the host or client issues a first command to the RAID controller to read specified data. After the RAID controller obtains the data from the RAID drives and transmits it to the host, the host verifies the data to detect any errors. If an error is detected by the host, the host issues a second command to the RAID controller to reconstruct the specified data, rather than merely re-read the data. The reconstructed data is then transmitted to the host. Consequently, previously undetected and uncorrected errors may be detected and corrected by the host.

Host-initiated data reconstruction for improved RAID read operations

A method, system, and article of manufacture for recovering from a track format error detected by a host computer associated with a storage controller associated with a storage disk array. The recovery method begins with saving a copy of the track format information associated with the data track that triggered the track format error in a predetermined location. Next, the track format information associated with the data track that caused the error is invalidated and the subject data is restaged. Subsequently, the restaged data is compared to the saved copy of the track format information to determine if the track format error exists with respect to the restaged data. If the track format error is detected with respect to the restaged data, the method further consists of reconstructing the data, preferably by performing a reconstruct read recovery. The reconstructed data is then compared to the saved copy of the track format information to determine if the track format error exists with respect to the reconstructed data. The method is completed by rebuilding the track format information to match the reconstructed data, writing the reconstructed data to the storage disk array, and passing the reconstructed data to the host.

Recovering track format information mismatch errors using data reconstruction

Servo errors can be avoided in a bi-directional reel-to-reel tape transport in which magnetic tape is moved in either of two opposite directions for data recording by providing a fine-line tachometer for each reel and a directly coupled tension sensor. Control of tape speed is implemented in a servo algorithm that uses tachometer inputs to determine parameter values for generating reel motor drive currents. If the linear velocity of both reels is the same then the tension output must be within a tolerable range. The directly coupled tension output provided an is indication of the actual current of the tension sensor. The difference between the linear velocities of the tape from each reel is calculated and monitored together with the tape tension. A trip level is set when an error occurs to stop tape motion and permit recovery without damaging the tape. The status of each outputs indicates the status of the tape velocity and whether the tape is slack or stretched on one reel which could cause a servo error which must be detected in order to prevent chopped blocks of data or data slivers. Motor problems may also be detected using the invention.

Servo error detection of bi-directional reel-to-reel tape drives using fine line tachometers

A method and system are disclosed for providing a hard stop for a robot included within an automated tape cartridge loading/unloading system. The system includes a tape drive having a loader which includes a movable loader tray. The loader tray is moved by a loader motor included within the loader. A determination is made of an insertion of a tape cartridge by the robot into a front of the tape drive. This determination is made utilizing a sensor included within the tape drive. In response to the determination, the tray is continuously held against the front of the tape drive while the tape cartridge is being inserted into the drive by the robot, thus providing a hard stop for the robot once the tape cartridge is completely inserted into the tray.

Method and system for providing a hard stop for a robot in an automated

Accurate tape servo track following is achieved by sampling servo edges at tape head alignments established with non-servo information, and processing the samples to (1) estimate optimal tape head index positioning to best align data as well as servo components, and (2) provide corrected position error signals (PESs) including a calculated error for comparison during ongoing servo track following to maintain the tape head at an optimal alignment for accurate alignment with the servo edges as well as data tracks on the tape.

Servo edge correction using edge samples taken by independently

Servo elements contained within a tape head detect a lateral displacement the magnetic tape relative to the tape head and generate position error signals corresponding to such lateral displacement. To aid in servo monitoring, the position error signals are sampled at predetermined times and the samples output or stored in machine-readable form. Each sample is classified as bad if it exceeds a predetermined threshold. Samples are analyzed to determine, for each time a bad position error signal occurs, how many successive position error signals are also bad. Samples are also analyzed to determine the relationship between bad position error signals samples and total samples. This data may be used for a number of different purposes. For example, this information may be used to identify differences between performance on top and bottom servo edges, or problems with the servo writing mechanism. Performance variations among different servo elements may also be identified. Such data may also be used to help recognize large 'dropouts' or 'fades' in the tape media. Furthermore, the data may also be analyzed to yield an overall indication of the media surface and edge quality of the media. Importantly, this information may be employed to pinpoint servo read errors, distinguishing between media problems and servo element malfunctions. Data obtained in accordance with the invention may also be used to evaluate tape media, with one possible implementation applying a numerical rank to factory-new tape media and subsequently binning the media according to their numerical ranks.

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Tucson, AZ, United States of America

Colleen Renee Stouffer