LTO: A better format for mid-range tape

In the last two years, Linear Tape-Open® (LTO®) tape drives have become clear leaders in the mid-range tape marketplace. Tape drives designed to the LTO Ultrium® format were the first of the super drives to be shipped to mid-range tape customers. This paper describes some of the eclectic features designed into the LTO format. The technical emphasis is on aspects of the logical format that are new or different from preceding drives, though some aspects of the LTO roadmap and physical format are also discussed. The logical format comprises all of the data manipulations and organization involved in writing customer data to tape. This includes data compression to compact the data, appending of error-correction codes (ECCs) to protect the data, run-length-limited encoding of the ECC-encoded data, prepending headers to the encoded data to make it self-identifying on read-back, and storing of information about the data and the way it is stored in a cartridge memory module. Physical format aspects that are discussed include encoding data into the servo pattern and write shingling. Also discussed are the format-enabled aspects of drive functionality that have been improved over previous tape drive products, including enabling backward writing, elimination of problematic failure mechanisms, dynamic rewrite of defective data, handling servo errors without stopping tape, and enabling robust reading. Contrasts are made with previous products and competing products based on other format choices. Also discussed throughout is the way in which an eclectic format can be created by cooperation among three format-development companies.