As other media are developing, tape is getting cheaper, more reliable and able to hold more data.
It allows you to re-read data stored in older archives and it's a low-cost solution. Brian Dooley looks back at the history of tape and examines options for the future.
Despite the vast amount of progress being made in optical media and other alternatives, tape remains a popular low-cost option for backup. Tape is a proven archival solution and provides a variety of special advantages for backup. One important factor is compatibility between tape generations, making it possible to re-read data stored in older archives. Tape technology is also low in cost per megabyte and has proven archive stability.
Because it has evolved gradually in a mixture of styles provided by different manufacturers, tape exists in a bewildering variety of formats, ranging from solutions designed for the desktop to solutions designed for enterprise network storage.
All of the major formats have shown a steady evolution, generally retaining some compatibility with previous generations. A number of new formats have also emerged recently which do not maintain compatibility with earlier tape but provide significant advances in capacity and data transfer rate.
At the low end, the most popular solutions are 4mm helical scan digital audio tape (DAT) and quarter-inch linear tape (QIC). Midrange and mainframe systems use a variety of tape storage systems, including the old reel-to-reel nine-track, IBM 3480/3490 and newer systems starting with 8mm.
With all tape systems, compression and error correction play an important role in determining actual capacity, reliability and data transfer rate.
These are software factors that can be difficult to gauge, however. Vendors rate most drives by a compressed capacity and rate, which is normally twice the "natural" for both areas.
Actual capacity and transfer rate greatly depend on the type of data being stored, however, and there are questions as to whether compression and error correction are implemented in software, hardware or firmware - and the resulting effect upon speed and efficiency. In this article, we have tried, wherever possible, to report the native capacities and rates.
Low-to-medium range storage. The low-to-medium range of storage is dominated by QIC, with a number of derivatives, and DAT. Versions of both are being developed for the high end of the medium range. These systems are commonly used on workstations; they may also be used to back up individual workstations in a network or to back up smaller networks.
QIC, introduced in 1972 by 3M, is a two-reel cartridge, with the reels driven by an internal belt. QIC uses linear recording to parallel tracks along the tape, with either MFM (modified fre-quency modulation) or RLL (run length limited) encoding.
QIC uses a stationary, linear read-write head, which the tape moves past at a rate of 100 to 125 inches per second. Performance is increased by adding read-write heads, to a maximum of about 36.
The format has suffered from a wide array of standards and lack of compatibility between standards. Formats include QIC-80, QIC-3010, QIC-3020, QIC-3080 and QIC-3095, which are now being replaced by Travan. The early formats contained up to 50 parallel tracks; later standards use 72 to 144 tracks.
Travan, an extension of QIC, provides higher storage capacities. TR-1 stores 400Mb (native); TR-2 stores 800MB; TR-3, 1.6GB; and TR-4, 4GB.
They have 36, 50, 50 and 72 tracks, respectively, and maximum data trans- fer rate (DTR) is 125Kbps, 125Kbps, 250Kbps and 70Mb/min. Compatibility with earlier QIC is good; all except TR-4 can read QIC 80.
The "TR" designation is being abandoned in favour of a simple GB rating - such as 4GB Travan - that better accommodates rapid expansion of this medium.
Tandberg's recently introduced Travan NS20 Pro stores up to 10MB (native), with a compressed DTR of 7.2 GB/hour.
DAT was originally a video format. In 1998, it became more widely used after Sony and HP defined the digital data storage (DDS) standard. DAT is a 4mm tape which uses helical scan recording, similar to video tape.
DAT uses a two-reel cartridge, but instead of simply streaming past the head, the tape is wrapped around a drum containing read and write heads. The drum spins at 2000rpm, and the tape moves in the direction opposite the spin at less than one inch per second, for a combined effective speed of 150 inches per second. Data is stored in short diagonal tracks across the width of the tape.
DAT has two formats, DDS and DataDAT, with DDS being most common. Current standards are DDS (2GB native), DDS-1 (2GB), DDS-2 (4GB), DDS-3 (12GB). Maximum data transfer rate (DTR) is 55Kbps, 1.1Mbps, 1.1Mbps and 2.2Mbps. Helical scan is slower than linear but its storage capacity is higher. DDS-3, used for networks, adds PRML (partial response maximum likelihood), a protocol devised to reduce the effects of noise.
Medium to large. The medium-to-large end of the tape market begins with the old mainframe reel-to-reel formats, but today's systems are more likely to use 8mm or DLT. These systems are used to back up media to large networks, minicomputers and mainframes.
Tape storage at the high end is often combined with library systems and autoloaders, which make backup more efficient and permit automatic storage of gigantic amounts of data. Hierarchical storage management (HSM) systems are also evolving; these systems distribute storage across various media according to need, optimising costs.
8mm tape was originally designed for video, but is now being used for data. It employs a helical scan technique (like DAT) but, due to added width, has a higher capacity than DAT. The basic formats are standard 8mm, Mammoth from Exabyte and Advanced Intelligent AIT from Sony.
Mammoth is a new 8mm format designed by Exabyte to be driven by a recorder with fewer parts than standard 8mm and a capstanless design to reduce wear.
AIT (advanced intelligent tape) is an 8mm design from Sony aimed at the midrange server market. The tape incorporates several breakthroughs, making it stronger, thinner and more stable. This is combined with new head technologies and a unique memory-in-cassette (MIC) feature, consisting of a 16KB EEPROM used to store all of the information generally place on the first segment of a tape, including directory information. The drive also incorporates IBM's advanced lossless data compression (ALDC) technology, providing hardware compression.
8mm includes standards from 2.5GB to 14GB (mainly Exabyte), with Mammoth holding 20GB in native format and AIT-1 holding 25GB in native format. Mammoth can read previous 8mm tapes, while AIT cannot. Maximum DTR is 32 to 120MB/min for standard 8mm, and 360MB/min for Mammoth and AIT.
Digital linear tape is a format developed by Digital Equipment in the 1980s. The technology was acquired by Quantum in 1994 and subsequently licensed to a variety of OEMs. DLT uses a single-reel design. When it is inserted, a leader tape interfaces with the end of the media tape and extracts it from the cartridge. It pulls the media internally in the tape drive and wraps it around an internal drum. Media is half-inch metal particle tape, with data stored in a serpentine pattern on pairs of parallel tracks, each track running the length of the tape. Additional tracks are added as the tape reaches the end and records in the opposite direction in a different position. This continues until the tape is full. Currently, DLT can contain either 128 or 208 tracks, with higher density achieved by angling the data pattern on adjacent tracks using symmetric phase recording (SPR).
DLT is recorded using a head guide assembly (HGA) featuring an aluminium plate with six large rollers which guide but do not pull the tape. Contact between tape and guide rollers is minimised, and the recorded side of the tape never touches the rollers. Tape movement is facilitated by a computer-controlled dual motor system. The net result is a head life of 30,000 hours compared to 2000 hours for 8mm helical scan.
Data is read and recorded using multiple simultaneous channels produced by a stationary head.
DLT also minimises search time by using an index located at the logical end of the tape.
This index is updated each pass and using 64 segments times the number of tracks has many thousands of addressable segments. Current DLT types are DLT2000XT (15GB native capacity), DLT4000 (20GB) and DLT7000 (35GB).
Data transfer rates are 2.5Mbps, 3Mbps and 10Mbps using compression. SuperDLT is expected to be available late this year, starting with 100GB native per cartridge and a product roadmap up to 500GB. While using new media called Advanced Metal Particle (AMP), SuperDLT will be read compatible with DLT4000 and DLT7000.
In its QIC format family, Tandberg provides its SLR and MLR technologies, which are suited to medium-to-large facilities. SLR has a 4GB capacity at 48Mb/min; MLR1 has a 16GB capacity and 1.5Mbps sustained transfer rate, MLR3 has a 25GB native capacity with a 2.0Mbps sustained transfer rate. Both SLR and MLR use a centre-loaded tape and multi-channel thin-film magneto resistive read head technology for speed and reliability, and a servo design.
Automating DLT backup
According to a Dataquest survey of mid-range tape systems, the DLT tape drive is the overwhelming market choice. And with 86 per cent of mid-market customers opting for DLT in 1997, vendors are making a commercial decision to push the DLT technology toward totally automated backup.
Automated backup is based on the presupposition that an organisation will need one backup tape per night, with cleaning and scratch tape also loaded to make sure that the backup is completed even if a fault occurs during the night.
Typically, users are able to purchase a single drive 5Ð10 cartridge autoloader that should allow hands-free backup for a week, as backup software takes charge over the lengthy process.
Recent product announcements from data backup specialist Overland claim to additionally enable Web access to their Data LXL DLT4000 based Loader, independent of the server and backup software that is used for configuration and diagnostic purposes.
This technology supports the ability to remotely set up, configure and monitor loaders and backups as is increasingly a market requirement.
Finally, adding to the attraction of the world of automated backup is the yet-to-be-released Quantum DLT8000 drive. Poised to become the first DLT drive to feature Variable Drive Speed that allows the drive to slow down or speed up according to the server transfer rate, the DLT8000 should reduce the stop/start action of current drives that is sometimes known as "shoe-shining". This feature will also be part of the SuperDLT 100GB per cartridge drive to be released later this year.
Andataco GigaSTOR/8000 (Deskside/Rackmount)The GigaSTOR/8000 (JBOD) series is an Ultra SCSI tape storage system.
Andataco provides continuous data availability with tape backup storage.solutions for UNIX and NT environmentsAvailable in rackmount and deskside tower models, this system provides storage for terabytes of data.
Features include redundant hot-swappable components, an Ultra-SCSI cableless backplane, proactive system, monitoring and management software.
The GigaSTOR Product Family houses 3.5in and 5.25in disk drives and tape drives (8mm and DLTTM ).
Andataco certified disk and tape drives are available in a wide variety of storage arrays within the GigaSTOR Product Family built with modular Enterprise Storage Packaging (ESP) enclosure technology:
GigaSTOR/3000 (Single-Ended or Differential) desktop system,GigaSTOR/8000 (Single-Ended or Differential) Deskside Tower System, or aGigaSTOR/8000 (Single-Ended or Differential) Rackmount System.
New Mammoth-LT tape drive
Exabyte's new entry-level addition to Mammoth tape platform.
High-reliability tape drive for small-to-medium business customers or for those in video, multimedia and sound production.
The Mammoth-LT delivers 28GB of capacity and 240MB/min throughput, and can back up 14.4GB in an hour, making it the fastest drive in its class.
Upgradable to the Mammoth 40GB/6MB/sec.
Mammoth-LT's format will be backward compatible with an installed worldwide base of more than 1.5 million Exabyte 8505XL and Elianta 820 drives, and libraries, further protecting the user's investment in Exabyte products.
Reliable robotics that automate backup procedures and data management.
Increased capacity over the stand-alone tape drive eliminates the chance for operator error and lowers data management costs.
Mammoth LT is available in internal or external Low Voltage Differential (LVD) and single-ended SCSI configurations.
8mm Tape Drive
Typical application: large department networks with application servers or automated libraries.
Multi-option SCSI-2 interfaces for easy integration to PCs, workstations and servers.
Fast data transfer rate (360MB/min) allows 43GB backup in less than two hours.
Flexibile architecture for easy software and O/S compatibility.
LCD display with drive status in multiple languages.
Advanced Metal Evaporated (AME) 8mm EXATAPE Data CartridgeDesigned specifically for use with Exabyte Mammoth drives.
Capacity of up to 40GB.
Archival life more than 30 years.
Dual layer, AME recording surface expands recording capacity, suppresses noise and improves data integrity.
Recording Surface Protective Coating (RSPC) increases tape durability, data security and long-term storage ability.
Low abrasivity and reduced head wear.
Over 20,000 passes on full-length data cartridge.
Exabyte 220 8mm Tape Library
Typical application: large client-server networks or departmental application servers.
Supported applications: unattended network backup/restore, remote storage, automated archiving, imaging and hierarchical storage management.
Capacity up to 800GB.
Data throughput of up to 43.2GB/hour.
Multidrive capability allows faster transfer of data and provides fault tolerance.
Removable magazines facilitate offline storage.
Front access to drives and media improves serviceability.
4mm data tapes offer
full automation for backing up the largest servers or networks.
High-output media provides reliable read/write operations.
Fast backup with 4mm drive technology.
Capacity 1.3GB, 2GB, 4GB, 12GB.
Usable lifetime of up to 2000 passes.
These pre-formatted, ready-to-use cartridges protect data from static-induced errors with a unique, anti-static drive belt and proprietary backcoated tape.
Assure uniform operation and safeguard data with Acculign baseplate and Dura-Stat II drive roller.
Available in a variety of formatted and unformatted capacities: DC 2000, DC 2120 and DC 3000.
Minicartridge accessories available.
Black Watch DLT Cartridges
Combine growing capacity and throughput in 1/2in format.
Fit a variety of midrange work environments, including workstations accelerating up the storage curve, growing LANs, and expanding data centres.
Cost-effective choice for large-file storage applications, including multimedia, databases, imaging, exploration, film, video and Internet.
Exclusive Imation Black Watch backcoating dissipates static to reduce errors caused by airborne debris, and minimises tape compression to protect recording surface from being flattened.
Travan NS 8GB
Read-while-write capability eliminates verify pass for data transfer rates up to 2MB per second.
Scalability increases total capacity with incremental improvements, instead of a complete overhaul.
Supported by top drive companies, including AIWA, Exabyte, HP Seagate, Tandberg Data and Tecmar.
Allows unattended, automated network backup.
Innovative 2:1 hardware compression doubles total capacity.
Built-in features improve performance and durability by reducing warping, dissipating static and decreasing exposure of tape to dust and debris.
Up to 1.2MB per second data transfer speedError rate of 10-8 or better.
740 feet of high-capacity 900 Oe Gamma Ferric Oxide magnetic media.
Preformatted per QIC-170.
DLT Tape IV
Suitable for rapid backup of network server and workstation data, and for DVD mastering.
Capacity 35GB (native), up to 70GB (compressed) with DLT7000 drive.
Capacity 20GB (native), up to 40GB (compressed) with DLT4000 drive.
Data transfer rate of 5MBps (up to 10MBps compressed) using the top-end DLT7000 drive.
Minimised tape and head wear with 500,000 pass reliability.
Tape tension servo control system and low-contact head.
All DLT systems designed to have backward compatibility.
Digital Data Storage (DDS) cartridges
Suitable for a wide range of needs, from PCs to servers.
Capacity up to 12GB.
Using helical scan technology.
High performance magnetic material for long-term archival storage and a low error rate.
High Cross Linkage (HCL) binder helps assure reliability under the stress of repetitive read/write operations.
RDP mechanism helps maintain smooth tape winding.
Advanced Intelligent Tape (AIT) cartridgesCapacity 25GB (native), up to 50GB (compressed).
Transfer rates of 3MBps (up to 6MB compressed).
Diamond Like Carbon (DLC) protective layer improves the tape's anti- abrasion properties and reduces error rates while maintaining high output.
The third-generation AIT-3 is scheduled to deliver up to 100GB native and 200GB compressed capacity.
Quantum DLT 7000 half-inch tape drive
Typical application: data storage and retrieval for backup, archive and near online applications in a professional environment such as workgroup networks, corporate intranets and enterprise computing.
Capacity: 35GB (native)
Utilises Symmetric Phase Recording Technique (SPR) and a four-channel recording system to achieve a native transfer rate of 5MB per second.
DLT 7000's head life is rated at around 30,000 hours.
Media reliability estimated at in excess of 1,000,000 media passes.
Works in UNIX, NetWare, Windows NT environments, as well as with proprietary operating systems.
Uses linear recording technology and the same tape guiding system and adaptive control mechanism as previous DLT drives.
Quantum DLT 4000 half-inch tape drive
Typical application: high-capacity tape backup for mid-range and high-end computer systems, such as high-end workstations, servers and network backup facilities.
Capacity: 20GB (native)
DLT 4000 deliver a sustained 1.5MBps native transfer rate.
Utilises dual channel read/write system and a tape mark directory to maximise performance.
The drive features Reed Solomon Error Correction Code, a 64-bit cyclical redundancy check and parity checking on the SCSI bus and internal data path.
Quantum DLT tape Media
The Quantum DLTtape family of half-inch cartridges, approved for use in all DLT tape drives and autoloaders, delivers the capacity of up to 35GB or 70GB in compressed mode.
A patented tape leader ensures consistent tape motion, while a unique tape/reel locking mechanism prevents tape slack to ensure accuracy.
A special high-grade metal particle (MP) formula reduces tape and head wear.
1,000,000 passes with soft error rates and a 30-year archival life.
Integration Systems (distributor for Andataco)Tel (02) 9975 5877 www.insyst.com.auExabyte 1800 350 350 Exabyte distributor: 1World Systems, a division of SealCorp Australia Tel (02) 9878 8888Imation Tel (02) 9479 9000Sony Tel (02) 9887 6666Digital Tape Solutions (distributors of Quantum DLT products). DTS also distributes Overland Data Tape ProductsTel (02) 9888 3488