User manual QUANTUM CL400LWXX

[. . . ] CERTANCE Online User's Guide LTO - 1 / LTO - 2 Ta p e D r i ve s i Copyright and Trademarks Copyright © 2003 by Certance LLC. Part Number 50001007 August 2003 Certance and the Certance logo are trademarks of Certance LLC. Other product names are trademarks or registered trademarks of their respective owners. Certance reserves the right to change, without notice, product offerings or specifications. [. . . ] Otherwise, a pointer to the invalid Codeword Pair is passed to the C1 ECC correction engine. · · If the C1 ECC correction engine can correct the error, then the corrected bytes are written to memory, and the Valid bit is set. Otherwise, the Valid bit is left cleared. As data is read from memory to the Data Processor for decompression, the C1 ECC is again checked and an interrupt generated if it is not correct. 40 Theory Data Integrity C2 ECC C2 ECC involves three distinct operations: 1. Encoding: Generating C2 ECC bytes from data bytes (performed by ECC co-processor hardware) Decoding: Generating ECC syndromes from data and ECC bytes, testing for all-zeroes (performed by ECC co-processor hardware) Correction: Generating corrected data from syndromes. The correction depends on the number and types of errors involved: · · · For one known C1 codeword pair in error in a sub-data set (C2 codeword), the operation is performed by the ECC co-processor hardware. For two or more known C1 codeword pairs in error, the matrix is computed by firmware and the correction is performed by hardware. For one or more unknown C1 codeword pairs, syndromes are generated by hardware, error location is computed by firmware, the matrix is computed by firmware and the correction is performed by hardware. Servo-tracking Faults During a write operation, if the servo system detects an error that may result in adjacent data tracks being over-written, the write operation is aborted. The write operation will not continue until the correct servo tracking is re-established. 41 Theory Data Compression Data Compression Typical data streams of text, graphics, software code, or other forms of data contain repeated information of some sort, whether it is at the text level where you can readily recognize regular repetitions of a single word, or at the binary level where the repetitions are in bits or bytes. Although most data is unique and random, the binary level data exhibits patterns of various sizes that repeat with varying degrees of regularity. Storage efficiency is increased if the redundancies or repetition in the data are removed before the data is recorded to tape. Data compression technology significantly reduces or eliminates redundancies in data before recording the information to tape. This increases the amount of data that can be stored on a finite medium and increases the overall storage efficiency of the system. With data compression, the redundant information in a data stream is identified and represented by codewords or symbols, which allow the same data to be recorded in a fewer number of bits. These codewords or symbols point back to the original data string, using fewer characters to represent the strings. Because these smaller symbols are substituted for the longer strings of data, more data can be stored in the same physical space. Some important benefits result from data compression in tape drives: · · · · The same amount of information can be stored on a smaller length of tape. Performance can more closely parallel to that of high-transfer-rate computers. More information can be transferred in the same time interval. Data Compression Considerations In an effective data-compression method, several factors are important: · The amount of compression. This ratio compares the amount of uncompressed data to the amount of compressed data. It is obtained by dividing the size of the uncompressed data by the size of the compressed data) The speed with which data is compressed and decompressed relative to the host transfer rate. The data integrity of the compressed data. · · · The amount of compression possible in a data stream depends on factors such as: · · · · · · Data pattern Compression algorithm Pattern repetition length Pattern repetition frequency Object size (block of information to be compressed) Starting pattern chosen The transfer rate depends on factors such as: · Compression ratio 42 Theory · · · · Drive buffer size Host computer input/output (I/O) speed Effective disc speeds of the host computer Record lengths that the host computer transmits Data Compression Data compression algorithms can be tailored to provide maximum compression for specific types of data. Because varying types of data are encountered in normal day-to-day operating circumstances, however, an effective data compression method for a tape drive must serve various data types. Additionally, the data compression method must adapt to different data types, automatically providing optimum handling for all types of data. Intelligent Data Compression The tape's compressed capacity is maximized through the use of intelligent data compression. The intelligent data compression hardware determines the compressibility of each record. [. . . ] If you insert a cleaning tape that is not expired but the tape is being ejected by the tape drive without performing the cleaning, you may see the message: "The last cleaning cartridge used in the tape drive was an invalid type: 1. Then use a valid cleaning cartridge. " This message means the tape drive does not recognize the cleaning tape as being of a valid type. You may have purchased a cleaning tape that is not supported by the tape drive. If the tape drive issues a message to backup software to instruct you to clean the tape drive, you may see the message: "The tape drive needs cleaning: 1. [. . . ]