Linear Tape-Open
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Linear Tape-Open (or LTO) is a magnetic tape data storage technology developed as an open alternative to the proprietary Digital Linear Tape (DLT). The technology was developed and initiated by Quantum, Hewlett-Packard, and IBM. The standard form-factor of LTO technology goes by the name "Ultrium".
In the late 1990s, Quantum's DLT and Sony's Advanced Intelligent Tape (AIT) were the leading options for high-capacity, high speed tape storage for PC servers and UNIX systems. Those technologies were and still are tightly controlled by their owners. Consequently, their availability were fairly limited. IBM, HP and Seagate sought to counter this by introducing a more open format.[1] Much of the technology is an extension of the work done by IBM at its Tucson lab during the previous 20 years.[2]
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[edit] Form factors
LTO technology was designed to come in two form factors, Ultrium and Accelis.
- Accelis – 8 mm tape, dual reel cartridge, biased toward fast access time, very similar to Sony's AIT product.
- Ultrium – 1/2" tape, single reel cartridge, biased toward high capacity, very similar to Quantum's DLT product and IBM's 3590 Magstar product.
As of 2006, LTO Ultrium is very popular and there are no commercially available LTO Accelis drives or media. In common usage, LTO generally refers only to the Ultrium form factor.
[edit] Accelis
Accelis was developed in 1997 for fast access to data by using a two-reel cartridge that loads at the midpoint of the tape to minimize access time. IBM's (short-lived) 3570 Magstar MP product pioneered this concept. The real-world performance never exceeded that of the Ultrium tape format, so there was never a demand for Accelis. Even Sony has acknowledged the popularity of the single reel, 1/2" form factor by producing the SAIT variant of their AIT technology.
[edit] Ultrium
1/2" magnetic tape has been used for data storage for more than 50 years. In the mid 1980s, IBM and DEC put this kind of tape into a single reel, enclosed cartridge. IBM called their cartridge 3480. DEC's DLT was later sold to Quantum. Both technologies have evolved since then and are still widely available. LTO Ultrium was developed as a (more or less) drop-in replacement for DLT. This made it easy for robotic tape library vendors to convert their DLT libraries into LTO libraries.
An Ultrium cartridge's dimensions are 102.0 x 105.4 x 21.5 (mm).
- An Ultrium drive is expected to read data from a cartridge in its own generation and at least the two prior generations.
- An Ultrium drive is expected to write data to a cartridge in its own generation and to a cartridge from the immediate prior generation in the prior generation format.
[edit] Generations
| Generation | LTO-1 | LTO-2 | LTO-3 | LTO-4 | LTO-5 | LTO-6 |
|---|---|---|---|---|---|---|
| Release Date | 2000 | 2003 | 2005 | 2007 | TBA | TBA |
| Native Data Capacity | 100 GB | 200 GB | 400 GB | 800 GB | 1.6 TB | 3.2 TB |
| Max Speed (MB/s) | 15 | 40 | 80 | 120 | 180 | 270 |
| WORM Capable? | NO | NO | YES | YES | PLANNED | PLANNED |
| Tape Thickness | 8.9 μm | 8.9 μm | 8 μm | 6.6 μm | ||
| Tape Length | 609 m | 609 m | 680 m | 820 m | ||
| Tape Tracks | 384 | 512 | 704 | 896 | ||
| Write Elements | 8 | 8 | 16 | 16 | ||
| Wraps per Band | 12 | 16 | 11 | 14 | ||
| Linear Density (bits/mm) | 4880 | 7398 | 9638 | 13300? | ||
| Encoding | RLL 1,7 | PRML | PRML | PRML? |
[edit] LTO-1
- Originally designed to come in 4 lengths of tape: 10, 30, 50, and 100 GB.
- Tape encoding is RLL 1,7
- First commercially available in September 2000.[3]
[edit] LTO-2
- Doubled capacity and transfer speed
- Switched to PRML encoding
- First mechanisms approved in February 2003.[4] First media approved in March 2003.[5]
[edit] LTO-3
- Doubled capacity and transfer speed again
- Introduced WORM feature
- Doubled number of write elements in head
- First media approved in November 2004.[6]
At the full native data rate (80 MB/s), LTO-3 drives can write data faster than most hard disk drives can read. Even the minimum streaming data rate (~30–40 MB/s) is faster than many hard disk drives.
[edit] LTO-4
- Doubled capacity again to 800 GB.
- Added 256-bit AES-GCM drive level encryption.
- Increase data transfer rate by 50% to 120 MB/s.
- First mechanisms approved in April 2007.[7] First media approved in May 2007.[8]
[edit] Notes
- Data Capacity and Speed figures above are for uncompressed data. Most manufacturers list compressed capacities on their marketing material. Capacities are often stated on tapes as double the actual value; they assume that data will be compressed with a 2:1 ratio (IBM uses a 3:1 compression ratio in the documentation for its Mainframe tape drives. Sony uses a 2.6:1 ratio for SAIT). See LTO-DC below. The marketing material also uses decimal definitions for byte capacities.
- The units for data capacity generally follow the (decimal) SI prefix convention. (eg. mega = 10^6)
- The units for data transfer generally follow the binary prefix convention. (eg. mega = 2^20)
- Minimum and maximum reading and writing speeds are drive dependent.
- Tape speed adjusts to available data stream, within the minimum and maximum streaming speeds.
[edit] Positioning times
Maximum rewind time is 98 seconds.[citation needed] Note that due to the back and forth writing, rewinding rarely takes this long. If a tape is written to full capacity, there is no rewind time, since the last pass is a reverse pass leaving the head at the beginning of the tape. Although this depends on the block size used when writing to the tape as the end of the tape could also be at the tape head when the writing is complete.
Average tape seek/filemark search time is 75 seconds.[citation needed] Although these times vary with the type of LTO drive that you have and the overall drive performance.
[edit] Tape durability
Estimated
- 1.2 million passes[citation needed]
- 30 years of archival storage[citation needed]
- 20,000 loads and unloads[citation needed]
To fill up a tape, LTO requires 48 passes, LTO-2 requires 64 passes, LTO-3 requires 44 passes, and LTO-4 requirs 56 passes. So the actual life of the tape is somewhat shorter than 1.2 million uses, total.
But even for LTO-2, which requires the most passes to span the entire tape, this still amounts to an estimated tape life of 18,750 full-tape reads and writes, which is 50 years of use when fully writing a tape every day.)
[edit] Technical features
[edit] Error detection and correction
The tapes contain a strong error correction algorithm that makes data recovery possible when lost data is within one track or up to 32 mm of the tape medium.[citation needed] When data is written to the tape it is verified by reading it back using the read heads that are positioned just 'behind' the write heads. This allows the drive to write a second copy of any data that fails the verify without the help of the host system.
[edit] Leader pin
The tape inside an LTO cartridge is wound around a single reel. The end of the tape is attached to a perpendicular leader pin that is used by an LTO drive to reliably grasp the end of the tape and mount it in a take-up reel inside the drive. When a cartridge is not in a drive, the pin is held in place at the opening of the cartridge with a small spring.
A common reason for a cartridge failing to load into a drive is the misplacement of the leader pin as a result of the cartridge having been dropped. The plastic slot where the pin is normally held is deformed by the drop and the leader pin is no longer in the position that the drive expects it to be.
Older tape technologies used different means to load tape onto a take-up reel. Some 9 track tape drives used a burst of air against the spinning reel to automatically separate and grasp the loose end of the tape. This worked without a leader pin. DLT tapes have a hole punched in the end of the tape that a drive can use to grasp the end of the tape.
[edit] LTO-CM
Every LTO cartridge has a Cartridge Memory chip inside it. It is made up of 128 blocks of memory, where each block is 32 Bytes for a total of 4096 Bytes. This memory can be read and/or written, 1 block at a time, via a non contacting passive RF interface. This memory is used to identify tapes and to help drives discriminate between the different generations of the technology.
Every LTO drive has a CM Reader in it. External readers are available, both built into tape libraries and handheld. The non-contact interface has a range of 20 mm.[9]
[edit] LTO-DC
The LTO specification describes a Data Compression method LTO-DC, also called Streaming Lossless Data Compression (SLDC)[10]. It is very similar to the algorithm ALDC[11] which is a variation of LZS (a patent-encumbered algorithm controlled by Hi/Fn[12]). The primary difference between ALDC and SLDC is that SLDC does not apply the compression algorithm to uncompressible data (i.e. data that is already compressed or sufficiently random to defeat the compression algorithm). More specifically, for each block of data that the algorithm works on, it saves a copy of the raw data and compares it to the "compressed" data. If the "compressed" data is larger than the raw data, it marks that block as raw and only saves the raw data to tape.
LTO-DC achieves an approximately 2:1 compression ratio when applied to the Calgary Corpus. This is inferior to slower algorithms such as gzip, but similar to lzop and the high speed algorithms built into other tape drives. It should be noted that plain text, raw images, and database files (TXT, ASCII, BMP, DBF, etc.) typically compress much better than other types of data stored on computer systems. In contrast, encrypted data and pre-compressed data (PGP, ZIP, JPEG, MPEG, MP3, etc.) would normally increase in size if data compression was applied. This expansion on tape is avoided by the SLDC algorithm.
[edit] Tape layout
LTO Ultrium tape is laid out with 4 wide data bands sandwiched between 5 narrow servo bands. The data bands are numbered 3,1,0,2 across the tape and are filled individually, in numeric order. The head unit straddles the 2 servo bands that border the data band that is being written or read. The servo bands are used to keep the head precisely aligned within the data band.
Data tracks are written in forward and reverse passes, also called wraps. It takes several wraps to completely fill a data band. All of the write elements in the head write simultaneously as the head passes over the data band from the physical start of the tape to the physical end. This makes one forward wrap. At the end, the head shifts to line up the write elements with a new set of tracks within the same data band. It is now ready to make a reverse wrap. All tracks written by the same write element in the same direction are grouped together. This leads to a set of serpentine patterns in each data band. To determine the number of passes required to fill up a tape, divide the total number of tracks by the number of write elements. For example, an LTO-2 tape requires 64 passes.
The block structure of the tape is logical so inter block gaps, file marks, tape marks and so forth take only a few bytes each. In LTO-1 this logical structure has CRC codes and compression added to create blocks of 403884 bytes. Another chunk of 468 bytes of information (including statistics and information about the drive that wrote the data and when it was written) is then added to create a 'dataset'. Finally error correction bytes are added to bring the total size of the dataset to 491520 bytes before it is written in a specific format across the eight heads. The formats for LTO-2 and LTO-3 are similar.
[edit] WORM
New for LTO-3 is Write Once Read Many (WORM) capability. This is normally only useful for legal record keeping. An LTO-3 drive will not erase or overwrite data on a WORM cartridge, but will read it. An LTO-3 WORM Cartridge is identical to a normal LTO-3 tape cartridge except its LTO-CM chip identifies it to the drive as WORM. There is nothing different about the tape medium in a WORM cartridge. Typically the WORM cartridges have a different color packaging.
[edit] Caution
[edit] Cleaning
Normal cleaning cartridges are abrasive and frequent use will shorten the drive's lifespan. HP LTO drives have a cleaning strategy[13] that will prevent the drive from actually using the cleaning tape if it is not needed. There is an internal mechanism that also handles cleaning tasks based on error rate criteria and time. The internal tape head cleaner is also activated when the cleaning cartridge is loaded.
[edit] Erasing
The magnetic servo tracks on the tape are factory encoded. Using a bulk eraser (or otherwise exposing the cartridge to a strong magnetic field) will erase the servo tracks along with the data tracks and make the cartridge unusable.
[edit] Cartridges
Compliance-Verified licensed manufacturers of LTO technology media are Maxell, TDK, Imation, EMTEC, Fujifilm, and Sony.[14] All other brands of media are manufactured by these companies under contract. Since its bankruptcy in 2003, EMTEC no longer manufactures LTO media products. Verbatim[15] and Quantegy[16] both licensed LTO technology, but never manufactured their own compliance-verified media.
[edit] Colors
The colors of LTO Ultrium cartridge shells are somewhat standardized. HP is the notable exception.
| UCC | LTO-1 | LTO-2 | LTO-3 | LTO-4 | |
|---|---|---|---|---|---|
| EMTEC | Black | Black | Purple | ||
| FujiFilm | Black | Purple | Slate-Blue | Green | |
| HP | Orange | Blue | Dark Red | Yellow | Green |
| IBM | Black | Purple | Slate Blue | Green | |
| Imation | Black | Purple | Blue-Gray | Teal | |
| Maxell | Gray | Black | Purple | Blue-Gray | Teal |
| Quantum | Black | Black | Purple | Blue | |
| RPS | Black | Purple | |||
| Sony | Black | Purple | Gray | ||
| StorageTek | Purple | ||||
| Tandberg | Grey | Black | Purple | Blue-Gray | |
| TDK | Gray | Black | Purple | Blue-Gray | Blue-Green |
| Verbatim | Black | Purple | Blue-Gray |
- UCC means Universal Cleaning Cartridge, which works with all drives.
- Different manufactures use different names for the same color sometimes. The names in the table above come from each manufacturers' own documentation.
- WORM (Write Once, Read Many) cartridges are two-tone, the top half of the shell is the normal color of that generation for that manufacturer, and the bottom half of the shell is a light gray.
[edit] Labels
The LTO cartridge label uses the bar code symbology of USS-39. A description and definition is available from the Automatic Identification Manufacturers (AIM) specification Uniform Symbol Specification (USS-39) and the ANSI MH10.8M-1993 ANSI Barcode specification.
[edit] Mechanisms
Current Compliance-Verified licensed manufacturers of LTO technology mechanisms are IBM, Hewlett-Packard, Quantum, and Tandberg Storage.[14]
[edit] Sales figures
| Year | Drives sold this year [17] |
Total drives sold (as of Sept.) [18] |
Cartridges sold this year |
Total cartridges sold (as of Sept.) [18] |
|---|---|---|---|---|
| 2001 | 1,000,000 | |||
| 2002 | 175,000 | |||
| 2003 | 262,000 | 350,000 (July) | ||
| 2004 | 354,000 | |||
| 2005 | 461,000 | 1,000,000 | 30,000,000 | |
| 2006 [19] | 1,500,000 | 50,000,000 | ||
| 2007 [20] | 2,000,000 | 80,000,000 |
- In 2002 LTO outshiped SDLT by nearly 2 to 1. Sales since then have dominated other "super" formats (SDLT, SAIT).
[edit] References
- ^ LTO (November 4, 1997). "HP, IBM, And SEAGATE Agree To Establish Open Format Specifications For Enterprise And Network Storage". Press release. Retrieved on 2007-10-15.
- ^ IBM storage history
- ^ LTO (November 05, 2001). "Linear Tape-Open Program Ships One Million Ultrium Tapes in First 12 Months of Availability". Press release.
- ^ LTO (February 12, 2003). "HP, IBM Pass LTO Ultrium Format Generation 2 Mechanism Compliance". Press release.
- ^ LTO (March 27, 2003). "LTO Program Announces LTO Ultrium Generation 2 Compliance-Verified Licenses". Press release.
- ^ LTO (November 08, 2004). "Fujifilm, Imation, Maxell, Sony, TDK Pass LTO Ultrium Generation 3 Data Interchange Compliance Testing". Press release.
- ^ LTO (April 11, 2007). "HP And IBM Pass Mechanism Compliance Testing For LTO Ultrium Format Generation 4 Tape Drives". Press release. Retrieved on 2007-10-15.
- ^ LTO (May 7, 2007). "Fujifilm, Imation, Maxell, Sony and TDK Pass LTO Ultrium Generation 4 Data Interchange Compliance Testing". Press release.
- ^ Fujitsu Cartridge Memory documentation
- ^ ECMA 321 – Specification of SLDC
- ^ IBM ALDC documentation
- ^ Patent claim by Hi/Fn
- ^ HP cleaning strategy
- ^ a b LTO Compliance-Verified Licencees
- ^ LTO (August 3, 1998). "EMTEC, IMATION, and VERBATIM License Linear Tape-Open Technology". Press release.
- ^ LTO (October 21, 1998). "Linear Tape-Open (LTO) Technology Continues Licensee Momentum with Signing of Fujitsu and Quantegy". Press release.
- ^ Freeman Reports
- ^ a b LTO consortium press releases
- ^ LTO (September 25, 2006). "LTO Ultrium Format Maintains Momentum With More Than 1,500,000 Tape Drives And 50,000,000 Cartridges Shipped". Press release. Retrieved on 2007-10-15.
- ^ LTO (September 5, 2007). "More than 2,000,000 LTO Ultrium Format Tape Drives and 80,000,000 Cartridges Shipped". Press release. Retrieved on 2008-03-13.
[edit] External links
- IBM's LTO Redbook – IBM System Storage Tape Library Guide for Open Systems
- Linear Tape Open – Consortium Homepage
- www.tandbergdatacorp.com/support/LTO1_2TapeUsersGuideFeb2.pdf Tandberg drive manual with lots of generic details (link inactive as of 2008-05-18)
- TDK brochure with a diagram of tape and cartridge construction
- ECMA 319 – Specification of Ultrium 1
- IBM LTO Ultrium Cartridge Label Specification, Revision 3
- An online generator for LTO barcode labels
[edit] See also
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