Ein Artikel aus 2002 zum Vergleich DLT - LTO
Dieser Text ist uns im April 2005 per E-Mail aus den USA zugesandt worden. Wir haben fast nichts verändert, nur kommentiert und teilweise übersetzt.
3 Jahre sind eine sehr sehr lange Zeit in der EDV und so haben sich manche Bewertungen des Marktes und auch die genannten Preise dramatisch verändert. Inzwischen hatte LTO (wie auch immer) bis Anfang 2005 angeblich 60-70% des Tape Marktes oberhalb von 100 Gigabyte erkämpft. Und ganz plötzlich hatte Quantum eine der drei Firmen aufgekauft.
Introduction (wie gesagt aus 2002)
With the growth of e-commerce and data-intensive applications, backups need to be stored more frequently, at a faster rate, and need to be reliable. There are two types of media that accomplish this: DLT and LTO. These tape technologies are widely used by most medium and large-scale networks. They are similar, yet each offers features that the other does not. There are also other backup devices available such as the 4mm DAT, 8mm, and quarter-inch (QIC).
LTO technology was designed to accommodate a range of storage requirements, from single server to complex network environments, in both fast-access and high capacity formats. For this reason, two implementations of the technology were developed: Ultrium and Accelis.
DLT tape systems are known for their outstanding performance, reliability, and storage capacity. Currently, DLT tape systems lead in market share in mid-range tape backup and archiving. There are many reasons why organizations need to make backups and archive data. One reason is due to the high “growth of Internet, Intranet, and e-commerce applications, many of which require constant backup of very large databases.” Another reason is due to the substantial increase in hard drive capacity and performance, which means the amount of data that needs to be backed up, continues to grow. Also, the move to client/server is another reason for tape backup. The DLT tape system is easy to use and is no longer used just for backups.
Historie der DLT Technik (bis 2002) von RDE
|Erscheinungs-Jahr||Model||Kapazität netto||Transfer Gewschw.||Band Länge|
|1989||DLT 260||2,6 GB||??||1.2000ft|
|1993||DLT 2000||10||1,25 MB/s||1.2000ft|
ergänzt durch RDE in 2005
|Erscheinungs-Jahr||Model||Kapazität netto||Transfer Gewschw.|
|2002 ??||S-DLT 320||160|
|2003 ??||VS 160||80|
|2004 ??||S-DLT 600||300|
History of DLT
In 1984 a group of engineers led by Fred Hertrick, from Digital Equipment Corporation developed a medium for system backup. Using the same conventional magnetic tape used in mainframe reel-to-reel systems, the team devised a drive that combined the qualities of a cartridge tape system and a reel-to-reel. This new device would use a cartridge that contained half-inch magnetic tape, but would only have one reel. This device later became known as the DLT Tape System. From 1984 to 1994 Digital introduced various models of the DLT system, each surpassing the previous model in storage capacity and transfer rate.
In 1994, Quantum Corporation acquired Digital’s disk and tape divisions. Quantum continued to introduce new products, which lead them to substantial growth in sales and market share. They increased the actual tape length from 1,200 feet to 1,800 feet and all models were backward compatible with previous models. In 2000 Quantum released the Super DLT tape technology, which can deliver over 1 TB of storage on a single tape cartridge. The Super DLT tape technology is considered “the next generation of DLT tape technology.”
The Super DLT is based on a Laser Guided Magnetic Recording (LGMR) technology, which uses a unique combination of the best of optical and magnetic technologies and increases the number of recording tracks on the media. Besides LGMR, the Super DLT tape technology uses five other advanced technologies to increase density and performance. Listed below are some of the DLT models, along with some specifications.
History of LTO
Linear Tape-Open is an open standard for a backup tape system, providing formats for both fast data access and high storage capacity, developed jointly by Hewlett-Packard, IBM, and Seagate. These companies have been jointly developing LTO technology over the last two years, and in August of 2000 IBM released the first LTO products. Like existing tape systems, LTO uses a linear multi-channel bi-directional format.
LTO adds to existing technologies timing-based servo (a device that automates a process of error correction for a mechanism), hardware data compression, enhanced track layouts, and efficient error correction code. Since not all users require the same features and functionality, two formats of LTO were created: Ultrium and Accelis.
Technical Description - LTO Technology
The LTO design is based in part on a bi-directional, multi-channel adaptations of linear technology already in use today. The LTO format specification divides the full tape width into smaller data bands to minimize the effects of tape shrinkage over time. The number of these data bands depends on the implementation: Ultrium has four data bands and Accelis has two. The tape head spans one band, and fills each data band sequentially. At the top and bottom of each data is a servo band. The servo bands provide location information to the head as it writes and verifies data tracks within that band. The process of positioning the head on the tape is a dynamic interaction between the head, the media and the servo elements of the system. The innermost bands are written first. To afford protection to data written in the outermost bands, two blank areas called edge guard bands border the top and bottom edges of the tape.
The cross-product ECC is interleaved both across tracks and along track over a large block size. This ECC is powerful enough to ensure reliable recovery of data even with the loss of one of eight tracks on a read operation and to 1% of the bytes on the remaining tracks being in error. Dynamic rewrite of bad blocks permits writing through a region of tape, which is bad in some tracks. IT is also powerful enough to permit recording a good copy of all user data even if one or more writes heads is nonfunctional. Beyond rewrite of bad data blocks, data is protected by dynamically discontinuing write operations in any region of tape were the servo’s position error signal is unreliable. The data is then rewritten down tape were the servo signals are again reliable. The reliable detection of format features, when used in conjunction with the precise LPOS data derived from the servo bands, allows position of formatted blocks on tape to be known with a precision exceeding any previous linear tape product. This allows rapid search operations and precise executioner error recovery operations (dramatically simplifying them).
Finally, the LTO-CM is an electronics and interface module, embedded in both the Ultrium and Accelis cartridges, which contains 4 KB (32 Kbits) for storage and retrieval of information about the cartridge and data. LTO-CM permits the drive to know where on tape a record exists without requiring reading of any directory or table off the tape. LTO-CM also permits blocks to be recorded with an absolute Write Pass number and sequence number. This permits simple determination and disregard of old data, as well as reliable read and write operations in even the most challenging environments. It can also contain user specified information. For example, a customer may need to store manufacturers data for warranty purposes, or data concerning the age of the cartridge, how many loads it has endured, how many temporary errors have accumulated, how much tape had been demarked, etc.
Technical Description - Ultrium Format
The Ultrium tape format is optimized for high capacity and performance with outstanding reliability, in either a standalone or an automated environment. The Ultrium tape format uses a single-reel cartridge to maximize capacity and is ideally suited for backup, restore and archive applications. The technology providers developed Ultrium to enable high-capacity, high-performance tape back-up solutions for the data storage industry.
Optimized for high capacity and transfer rates, Ultrium provides a technologically solid migration path that allows for maximum expandability. The first generation of this technology allows for storage of up to 100GB of data (>200GB compressed) on a single cartridge at data rates as high as 20MB/sec. (>40MB/sec. Compressed). The performance is made possible through the use of linear recording techniques that employs either a four or eight channel head and closed loop servo technologies. The high capacity results from applying LTO to a new data cartridge that ahs been designed to maximize the amount of tape surface area while still enabling very small form factors. The cartridge has a locking mechanism that maintains pack tension during shipping and storage. It also has a write-protect mechanism identified by a visual lock mark when in the “protected” position. A cutout in the front side of the case prevents the cartridge from being inserted into the drive upside-down. This feature also prevents the use of unsuitable cartridges of similar, but not identical construction.
Ultrium offers a clear migration path. Maximum transfer rates and native capacity are intended to double in successive generations of the product line. Second, third, and fourth generation products are intended to deliver a better than 30 percent increase per generation in the number of tracks. Third generation products will also offer improvements in the maximum tape length, and fourth generation products will employ more advanced recording media.
Technical Description - Accelis Format
The Accelis tape format is optimized for fast access to data, with exceptional reliability and performance characteristics. Using a two-reel cartridge that loads at the middle of the tape to minimize access time, the Accelis tape format is targeted at automated environments and can enable a wide range of ‘online’ data inquiry and retrieval applications. The Accelis format will utilize all the advantages of LTO described for Ultrium except that the capacity has been reduced for the purpose of improving the access time to data dramatically. The capacity reduction is the result of making the tape narrower (hence fewer tracks) and by putting two reels in the cartridge instead of one. This results in 216 meters of 8mm wide tape, which contains 25GB of data (>50GB compressed). The dual real cartridge implementation provides a number of advantages. Because the tape path is fully contained in the cartridge, the tape can be loaded at the mid-point, which, in conjunction with the eliminated thread time, improves search times to sub-10 second averages. The Accelis implementation of LTO is an ideal choice for automated tape solutions focusing on digital library applications and other read intensive tape applications.
Accelis records the LTO format in two date bands instead of four for Ultrium and each data band contains 128 tacks (256 tracks total). Like Ultrium, the data bands can be recorded with eight-channel or four-channel heads and eight servo positions are defined in the servo band to support the recording. The very unique aspect of Accelis cartridge design is that the media could be pre-positioned or post-rewound to further improve system performance.
Also, in conjunction with the LTO-CM, and offline device (such as a smart picker or a queing device) can locate to a specific point on tape prior to tape derive insertion. This is a very powerful concept that will enable unprecedented solutions unique to Accelis.
Accelis offers a clear migration path. Maximum transfer rates and native capacity are intended to double in successive generations of the product line. Second, third, and fourth generations products are intended to deliver a better than 30 percent increase per generation in the number of tracks. Third generation products will also offer improvements in the maximum tape length. Forth generation products will employ more advanced recording media.
Hier ein einfacher Vergleich
Warum gibt es zwei LTO tape formate?
Two formats were created because not all users require the same features and functionality. Some applications are read-intensive that require the fastest access to data. And other applications are write- intensive and fill tape cartridges very quickly, which requires the highest single-tape-cartridge capacity possible. Accelis is for fast access and Ultrium is suited for high-capacity environments. Plasmon s new tape automation offers automation utilizing the Ultrium format. Plasmon will also support LTO Accelis when the drive is available with its proven MP-series automation line.
Warum sollte man Ultrium wählen ?
The tape market is flooded by a variety of proprietary tape formats. This has lead to customer confusion. LTO changes this dynamic. Ultrium offers an open tape storage solution that can be licensed by any manufacturer. As a result, Ultrium has endorsement in the tape storage industry and is backed by a multitude of hardware and media licensees. And as said above the Ultrium format is based on the best-of-available technologies to meet the capacity, performance and reliability needs of today s demanding storage environment.
Technical Description - DLT Technology
The DLT Tape system uses half-inch wide tape, which is bigger than other widely used technologies, i.e. Quarter-inch (QIC), 4mm, and the 8mm tape. DLT tape drives also read and write data in a linear pattern. For example, when data is being recorded, each track goes the entire length of the tape. Once the end of the tape is reached, the heads are repositioned to record a new set of tracks, and this time the recording is done in the opposite direction. This process continues until the tape is full. In the DLT 7000 and DLT 8000 Drives, writing the data in an angled pattern, allowed for more capacity and increased data density.
The Head Guide Assembly (HGA) also makes the DLT tape technology superior to others. This is a patented design and is different than other competing technologies. These Helican Scan (AIT) HGA systems are designed to move, and must reach out and hook the tape and wrap it around the read/write drum. This then holds it in position and moves the tape back into the cassette. The DLT tape HGA is completely different. First of all, it remains stationary. As mentioned before, the DLT tape system consists of six precision rollers. The tape is gently pulled out of the cartridge and is guided around the HGA, which gently wraps the tape around the take-up reel in the drive. It is important to note that because the rollers guide the tape, the contact between the guide and the tape is minimized, which reduces tape wear. The HGA in the Super DLT tape drives has now incorporated only four rollers, which reduces the contact between the tape and the guides even more.
The DLT tape system is unique because it has only one reel. The take-up reel was built into the unit itself. This convention allowed the actual cartridge to be fully filled with tape, instead of half filled with air and another reel. This explains why these tapes are heavier and have higher capacity. The cause for elimination of two reels allows more space for tape and storage capacity.
S-DLT oder LTO im Tabellen-Vergleich (aus 2002)
|Quantum S-DLT 220||IBM LTO||Seagte LTO|
|Kapazität netto||110 GB||100 GB||100 GB|
|Transfer geschw.||11 MB/s||15 MB/s||16 MB/s|
|Sicherungs Rate||ca 40 Giga/Std||ca 54 Giga/Std||ca 58 Giga/Std|
|Verkaufspreis Drive||5.000 US $||4.800 US $||5.300 US $|
|Verkaufspreis Band||127 US$||124 US$||124 US$|
Der Vergleich (aus 2002 !!)
When comparing DLT and LTO, many attributes come to mind: speed, core technology, market share, storage, compatibility, and cost. To begin, there are two disciplines of speed, the transfer rate and the backup rate. For Quantum, the DLT tape system is its core technology. However, for the companies behind LTO (IBM, Seagate, and HP) it is not their core technology. LTO does however; provide customers with these powerful benefits, seamless data interchange and unprecedented levels of scalability, reliability and performance, as well as faster paced innovation, lower prices, and true multivendor compatibility.
LTO’s logical format permits a higher recording density than any linear tape technology available in the industry.
About the Technology-