MTCs Will Continue To Be Enterprise Storage's Choice For Removable Storage Media.
It seems unlikely that the 15-year-old magnetic-tape-cartridge storage medium will be the removable medium best suited to the ever-growing needs of enterprise storage in the next decade, but the development and refinement of the half-inch MTC medium has kept pace with enterprise computing's evolving and growing storage needs. The familiar MTC medium has the promise of further advancement.
MTCs are attractive to enterprise storage because they offer reliable, low-cost storage. They have everything going for them except interchangeability. There are no industry-wide standards to allow the easy transfer of data from one system to another. This lack of MTC standardization forces data centers to choose among manufacturers different proprietary standards to achieve the efficient leveraging of data necessary to their enterprises' strategic use of information and competitiveness. Now that Y2K projects are off the plates of data centers, it is time for many of them to determine their storage options and make those choices.
This article looks at:
* Current enterprise storage trends favoring the use of MTCs
* Recent MTC developments and design features
* Five state-of-the-art proprietary half-inch MTC products standards competing for enterprise storage's tape backup, archiving, off line-storage etc.
Storage Trends And Magnetic Tape Cartridges
The continuing information explosion, as well as new systems for image acquisition and processing of aerospace, healthcare, geophysics, and video-on-demand applications require greater storage capacities and quicker access times. To accommodate this ever-increasing amount of data, data centers must expand the capacities of their fixed disk drives, as well as increase the storage capacities of their tape backup devices.
While MTCs remain the choice for archival and near line storage, further automation and special software like Virtual Tape Systems (VTS) leverage magnetic tape cartridge's cost advantage. Industry statistics indicate that cartridges are used on average to 30 percent of capacity. VTSs do data stacking and fill up their virtual tapes. So when the data is transferred to real tape cartridges, they are in rum filled close to capacity, reducing the number of MTCs required to back-up and archive data.
There are some 60 million MTC slots in installed robotic tape libraries around the world. This installed base gives the MTC an overwhelming inertia or resistance to replacement for the next several years. The unfortunate irony is that these tape slots are the only commonality of MTC-based storage systems.
Over the past thirty years, the amount of recording tracks on half-inch tape media has increased from seven tracks to about 400 tracks and the recording density of tape media has increased from 800bpi (bits per inch) to the 90,OOObpi range; this is a 6,000 or 7,000 fold increase. Tape media recording tracks and bpi will continue to increase in similar increments over the next decade. The storage capacity of the MTC has grown in the past decade exponentially from 200MB to capacities outlined in the Table; (unfortunately quite a few of these new drives are not, or will not be, backwards compatible with their manufacturer's existing products.) As shown in the Table, two completely different methods are used to store and retrieve the information on the media. The helical scan recording method uses a slow moving tape (the Redwood drive, for instance, has a tape speed of 3.3inchlsec) and heads mounted in a drum rotating at around 1800rpm. In contrast to this, the linear recording method employs a serpentine recording method with one or multiple heads and a tape having a speed of up to four meters per second.
Although media manufacturers have optimized their formulations for each of the recording methods, the helical drives have a more aggressive head to media contact and more complicated tape paths. Some of these drives also employ a pinch roller that has contact with the data side of the media. In the linear recording tape drives, there is a gentle contact between the stationary head and the media and most stress components are in the direction of the tape motion, instead of perpendicular to or against the tape motion. This results in less wear and tear in applications where there is a lot of media shuttling. Most experts agree that 50-100 uses are a good life span for helical tape media.
In enterprise storage, linear recording is the dominant format in all half-inch tape technologies, including DLT, 9840, 3480/90, and 3590, as well as the 8mm 3570. There are very few helical systems in enterprise storage. Helical is prevalent in video tapes. If its tendency to wear down media can he overcome, it has great potential for increasing the number of recording tracks over the current standard as shown in the Table.
One inefficient result of these high capacity cartridges is the practice of double backups. Apparently, data center managers are not comfortable with having so much data on any one cartridge and with some good reason. If there is a problem with one of these new high capacity cartridges and a block of data cannot be read from it, then the rest of the cartridge cannot be read by the data center. Another downside of the high capacity MTC is the security risk. One cartridge can hold a lot of data and is easily concealed.
To fully leverage enterprise data, data centers are consolidating hardware and software into fully compatible high capacity systems with improved access and performance. These systems feature the new high capacity tape storage platforms. The days of multiple hardware platforms and operating systems working with multiple databases and software configurations within one enterprise are coming to a close.
As storage capacities and the amount of data to be stored grow, the rapid accessibility of data across the enterprise becomes increasingly important. Unfortunately, today the new magnetic tape cartridge backup and archiving storage systems are characterized by the technically different proprietary standards of each system's manufacturer. Even Linear Tape Open, LTO, is somewhat proprietary because it is not standardized globally. These standards reduce competition and tend to keep prices from falling to commodity levels.
Eventually, they will force users to choose one standard in order to achieve the full benefits of leveraging data across an enterprise. The question is will the user community accept this structure? Until recently, enterprise storage users were contending with the Y2K issue. By its nature, Y2K made users less willing to jump into new, relatively unproven tape technologies during that critical period of backup. It made them more receptive to refinements of well-established mainframe tape technologies, like the new 1GB 3490 cartridge and virtual tape systems.
Developments And Differences In Current MTC Technology
For each new magnetic tape cartridge storage system, the tape drive manufacturer, in cooperation with one or more selected media manufacturers, must balance the following key parameters to create a low cost, high capacity, reliable drive with optimum access time. The different ways this balancing process is achieved is what accounts for the different proprietary standards characteristic of MTC brands.
A. Reduced recording track width and use of servo-track technology
B. Increased recording density and its implications
C. Implications of increasing the tape length
Increased storage requirements have outstripped the mechanical track position abilities of the MTC drives. Servo-tracks were introduced to make it possible for record/playback heads to position themselves accurately over the tape. The concept behind servo-track positioning is to pre-record two or more tracks on the media. The record/playback head also contains read heads specifically for reading these pre-recorded tracks, thus enabling the head to position itself accurately on the media and interpolate the location of other numerous data tracks between the servo-tracks. Most new MTC tape drives use a variation of this proven servo concept, while the Super DLT uses a new optical servo technology, the Pivoting Optical Servo (POS). On the negative side, a cartridge with servo tracks cannot be degaussed because erasure would remove the head positioning ability of the drive (This is not the case with SDLT.).
Tape Coating/Formulation And Cartridge Design
To increase the track and recording density (capacity for data measured in bits per inch) of magnetic tape, smaller, more powerful magnetic particles must be used in a tape's magnetic coating. The need for increasing BPI mandates a thinner, smoother, high output layer of magnetic coating with a low error rate. Magnetic tape formulations have progressed from iron pigment (reel-to-reel) to chrome pigment (3480/90) to metal particulate, MP, (LTO) to the emerging metal evaporated, ME, or AME, using cobalt particles. AME media is currently used in some helical scan tape cartridges to enable higher bit and track densities.
The thickness of magnetic coatings has decreased to the point that it is influenced by the surface roughness of the tape's underlying base-film. An improved clean-room environment is required for the manufacturing of media to tolerances in that magnitude. To overcome the surface roughness issue and give the media physical characteristics closer to older-generation thicker media, an undercoat is applied to the base film. This dual layer coating technology places a non-magnetic base coat over the base film to smooth out surface roughness and to improve the thin media's stiffness and durability. This enables the tape to withstand the stress of being run repeatedly through a tape drive.
To obtain better physical characteristics for thinner media, new and improved base films are being developed. Unfortunately, they do or will carry a higher price tag.
The consequence of a longer tape length in a cartridge is increased data access time. To improve access time, the tape media in some of the cartridges is "parked" in the middle. Half of the tape is on one reel and half is on another. This required the use of two reels in the cartridge, reducing the amount of space for the media (i.e., shorter piece of tape), for example, lower storage capacity than the single reel cartridge. The access speed advantage does, however, disappear if initial access to more than one position is required. The dual reel design option also shifts the responsibility of manufacturing a stable and reliable tape path and tension control to the media manufacturer, which in turn increases the cost of the media. The 3590, for example, is a single reel device, while the 9840 is a dual reel device.
Some of the new cartridges, like AIT and LTO, have a MIC (Microchip In Cassette) feature, allowing the transmission of file access/file location data to the drive without actually mounting the tape. This placement of memory chips, i.e. "electronic labels," inside the shell of each magnetic tape cartridge will allow immediate access to a much more in-depth description of the data on each cassette and enable significantly improved data organization and improved library efficiency.
New Mainframe/Server Magnetic Tape Cartridge Systems--A Choice Of Proprietary And International Standards
IBM 20GB Magstar - The 3590E has 20GB native capacity. It has a single reel, uses linear recording, and the same cartridge as the 10GB product. It is competitively priced and available from more than one manufacturer. 40GB media will be announced for year 2000 delivery. It has 256 tracks, plus three servo tracks.
Linear Tape Open Ultrium-This has 100GB native storage capacity with a single-reel, linear recording format. Drives are being made by IBM, Hewlett-Packard, and Seagate who formed the Linear Tape Open Consortium to introduce an open MTC standard into the marketplace. As of last count, five media manufacturers have obtained LTO licenses to produce an Ultrium product to LTO specifications. The LTO is less proprietary than the other MTC products and could become a worldwide standard. Drives and cartridges will be available in the first half or 2000. Ultrium has 384 tracks plus servo tracks.
Super DLT - This has linear recording and the new Pivoting Optical Servo format. It will compete against the LTO Ultrium. It has a 100GB native storage capacity with 416 tracks. It is scheduled for delivery in 2000. A limited number of hardware and media manufacturers will support it.
StorageTek 9840 - This 20GB native storage capacity, linear track design, two reel medium fits in a standard MTC silo. This tape cartridge offers both speed and capacity, but it is only available from one manufacturing source under various brand names. (288 tracks plus three servo tracks.)
Linear Tape Open Accelis-Accelis ill be a 25GB, dual-hub cartridge, similar to the current IBM 3570 cartridge and will be built for speed, making for fast tape access. It will use 8mm media and be targeted for the mid-range/open system/server environments. Deliver is expected in 2000.
AIT-2 - Containing 50GB native storage capacity, it is a helical scan recording tape system using 8mm media. This product, along with the Mammoth 2, is targeting the mid range/open system market.
It should be noted that none of the above cartridges would fit into existing robotic tape silo without some kind of modification. The Aegis Tape Library, recent offering from StorageTek, has addressed this problem and supports mixed media, including LTO, DLT, SDLT, Ultrium, and 9840 due to the similarity of the cartridge sizes.
High capacity magnetic storage for enterprise data systems will continue to focus on magnetic tape in the next decade. New tape drives and MTC storage systems will have innovative features to reduce access time and increase performance Storage on magnetic tape will continue to grow exponentially. LTO/Ultrium specifications, for example, call for an 800GB cartridge by 2008 (The first generation Ultrium has 100GB of native capacity.). Double backups will be a byproduct of these ever-increasing capacities. Technically, the question will be how many exponential jumps in bpi can metal particulate technology support. Metal (cobalt) evaporated media is most likely the next step, but will it have the needed mechanical properties we have gotten used to? Its cost must come down. As bit density goes up and tape coatings become thinner, the tape surface will become smoother, but still should be able to withstand the wear and tear of daily use.
Magnetic tape cartridges are small. They are removable. They are reliable and they are inexpensive. Their storage cost per megabyte is the lowest. These four simple reasons are why MTCs will remain the choice of data centers for backup and archiving for several more years. Leapfrogging proprietary technology and advancements have led to a market governed by proprietary standards. Currently, LTO offers a possible path away from the continuation of proprietary standards into the foreseeable future.
Gerrit Nijssen is the director of applications engineering at EMTEC DataStoreMedia, the North American Subsidiary of EMTEC Magnetics GmbH (Bedford, MA).
Media Format Present Near Term Future Mini data cartridge Linear 10GB 15GB 0.25-in. Cartridge Linear 25GB 50GB 8mm 3570/LTO Linear 5GB 25GB 200GB 0.315-in. (Travan) Linear 20GB 30GB 100GB 0.500-in. Cartridge Linear 40GB 60GB 100GB 0.500-in. LTO/Ultrium Linear 100GB 800GB 8mm Helical Scan 20GB 60GB 200GB 4mm Helical Scan 12GB 24GB 48GB 12.65mm Helical Scan 40GB 100GB 200GB 19mm Helical Scan 100GB 300GB 400GB
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|Title Annotation:||Technology Information|
|Publication:||Computer Technology Review|
|Date:||Jan 1, 2000|
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