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. Seagate is a trademark of Seagate Technology LLC. Other product names are trademarks or registered trademarks of their respective owners. [. . . ] 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. More data can be stored on a given 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. The amount of compression is measured by the compression ratio. 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 the size of the record is larger after a compression attempt than the native (uncompressed) size, then the record is written in its native form. The intelligent data compression utilizes two compression schemes: · · Scheme-1 is a LZ1 based compression scheme using a history buffer to achieve data compression. Scheme-2 is a pass-through compression scheme designed to pass uncompressible data through with minimal expansion. There are three specific requirements for compliance with the LTO specification. · · · First: the output data stream must be decompressible following LTO rules to create the input sequence of records and File Marks perfectly. Second: an LTO compressed data stream may not contain any of the eight reserved Control Symbols. Third: while control symbols allow switching to Scheme 2, this should never be used by operational software because this capability is only for diagnostic and testing purposes. Software data compression should never be used because the LTO-1 and LTO-2 drives' built-in intelligent data compression is much more efficient than software data compression systems. The LTO-1 and LTO-2 drives use a derivative of ALDC-2 lossless data compression that includes additional control codes for intelligent data compression. 43 5. Specifications This chapter provides technical specifications for the LTO-1 and LTO-2 drives. The topics covered in this chapter are: · · · · · · · · "Physical Specifications" on page 44 "Power Specifications" on page 47 "Drive Performance Specifications" on page 48 "Environmental Requirements" on page 49 "Reliability" on page 50 "Mean Time Between Failures" on page 50 "LTO Cartridge Specifications" on page 51 "Regulatory Compliance" on page 52 Physical Specifications Table 8 on page 44 lists the physical specifications of the LTO-1 and LTO-2 drives. [. . . ] If the operation has stopped, eject the tape and clean the drive. If the operation has not stopped, wait for it to finish and then clean the drive. Check the tape drive users manual for device specific cleaning instructions. " This message means you should use a supported cleaning tape. 86 Troubleshooting Guide Manually Removing a Cartridge Slow Backups There are many factors that can make backups appear to be "slow. " To achieve the highest possible transfer rate, the LTO-1 or LTO-2 tape drive MUST be attached to a Low Voltage Differential ( LVD ) SCSI controller capable of a minimum of 80 MB/s and MUST not share the same SCSI bus as another active SCSI device such as hard drives. Is the tape drive attached to an LVD SCSI controller? [. . . ]