Exabyte has been a leader in the tape storage industry for more than a decade, pioneering the use of 8mm tape for backup, incorporating Sony’s camcorder-based mechanisms into over 1.5 million tape drives. While camcorder-based mechanisms are adequate for low duty cycle applications, it is less appropriate for today’s demanding server-based applications. Introduced in 1996, Mammoth is a more advanced and reliable technology and represents Exabyte’s response to the requirements of this mid-range server market.
Mammoth features an Exabyte-designed and manufactured deck with 40 percent fewer parts than previous 8mm drives and specifically designed to improve reliability by reducing tape wear and tension variation. A solid aluminium deck casting provides the extra accuracy and rigidity needed to maintain tight tolerances. The casting shields the internal elements from dust and contamination and directs heat away from the tape path. A three-point shock-mount system isolates the casting from the sheet-metal housing, providing protection from external forces. With seven custom application specific integrated circuits (ASICs), Mammoth calibrates itself regularly, searches for and reports any errors.
The capstanless design eliminates the part of the tape drive that creates unpredictable wear and exerts the most pressure on the media. Without a capstan, damage to the edge of the tape is prevented during repositioning. The gentle tape path supports advanced metal evaporated (AME) media, a thinner, more sensitive media expected to emerge in the future. AME is a data-grade tape, which stores more data per cartridge. Its anti-corrosive properties improve tape durability and reduce tape wear, allowing the media to achieve a 30-year archival rating. The smooth surface is a key element behind Mammoth’s head-life specification of 35,000 hours. In addition, Mammoth’s custom scanner is optimised to operate with the AME media.
Mammoth supports up to 64 variable-length partitions. A partition is a segment of tape that is used as an entity into itself. Data within a predefined partition can be erased and new data written in its place. This feature will become more valuable as media capacity continues to grow, allowing Mammoth to support such applications as multimedia and video servers.
Preserving data is paramount in a tape storage product. Error correction can make or break the reliability of the device. Mammoth uses a two-level Reed-Solomon ECC. Exabyte’s ECC corrects errors on the fly by rewriting the blocks within the same track.
Exabyte’s Mammoth-2 drive set new standards of high speed and capacity in the tape market when it was introduced in late 2000. The drive has a quoted native transfer rate of 12MBps, while the 8MM AME tapes can store a maximum of 60GB. Along with an Ultra 2/LVD SCSI interface and a huge 32MB buffer, the drive uses a new multichannel helical scanning head, the latest ECC3 error-correction algorithms and offers a 2.5:1 compression ratio using ALDC (Adaptive Lossless Data Compression) for a maximum capacity of 150GB per tape. A subsequent fibre channel version offered an increased native DTR of 30MBps.
The introduction of the Mammoth marked the end of a period in which tape backup had been viewed as a very conservative medium whose capacities and transfer rates increased only slowly, and certainly far behind the speed of improvements in magnetic disk and other random access technologies. In the second half of the 1990s several new tape formats were to be launched which provided levels of performance and storage capability commensurate with the hard disk capacities that had been reached by the end of the millennium.