User manual QUANTUM LTO-4

[. . . ] Quantum LTO-4 Half-Height Tape Drive User's Guide, P/N 20020140-001, November 2007. Quantum Corporation provides this publication "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability or fitness for a particular purpose. Quantum Corporation may revise this publication from time to time without notice. Making copies or adaptations without prior written authorization of Quantum Corporation is prohibited by law and constitutes a punishable violation of the law. [. . . ] C1 ECC As data is written to memory from the data processing unit, the DMA/ ECC interface generates C1 ECC bytes and writes them to memory. As data is written to tape, the C1 ECC is checked and an interrupt generated if there is an error. When data is read from tape and stored into memory, C1 ECC is checked and: · If the C1 ECC is good, the "Valid" bit for the codeword pair is set. · 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. 4 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. C2 ECC C2 ECC involves three distinct operations: 1 Encoding: Generating C2 ECC bytes from data bytes (performed by ECC coprocessor hardware). 2 Decoding: Generating ECC syndromes from data and ECC bytes, testing for all-zeroes (performed by ECC coprocessor hardware). 4 LTO-4 Half-Height Tape Drive User's Guide 26 Chapter 4 Theory Data Compression 3 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 subdata set (C2 codeword), the operation is performed by the ECC coprocessor 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 4 During a write operation, if the servo system detects an error that may result in adjacent data tracks being overwritten, the write operation is aborted. The write operation will not continue until the correct servo tracking is re-established. 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 that allow the same LTO-4 Half-Height Tape Drive User's Guide 27 Chapter 4 Theory Data Compression 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 4 In an effective data-compression method, several factors are important: · The amount of compression, which is measured by the compression ratio. [. . . ] See Cleaning the Tape Drive on page 20 and use a valid LTO-type cleaning cartridge to clean the tape drive. the tape drive has issued a message to the backup software to instruct you to clean the tape drive. See Cleaning the Tape Drive on page 20. LTO-4 Half-Height Tape Drive User's Guide 62 AInstallation Checklists Appendix A Use the following quick-start checklists to get your tape drive up and running as quickly as possible: · Internal LTO-4 Half-Height Tape Drive Quick Start · Tabletop LTO-4 Half-Height Tape Drive Quick Start LTO-4 Half-Height Tape Drive User's Guide 63 Appendix A Installation Checklists Internal LTO-4 Half-Height Tape Drive Quick Start Internal LTO-4 Half-Height Tape Drive Quick Start Use the following quick-start procedure to install the internal LTO-4 Half-Height Tape Drive. If you need more information about a step, see the sebsection referenced in the step. [. . . ]