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Linear Tape-Open
From Wikipedia, the free encyclopedia
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 Seagate, 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]
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).
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]
LTO-DC achieves an approximately 2:1 compression ratio when applied to the Calgary Corpus. This is inferior to slower algorithms such as bzip2, but similar to 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 compression was attempted. This expansion on tape is prevented by the LTO tape drive's detection of uncompressible data.
Average tape seek/filemark search time is 75 seconds.
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.
The servo bands are used to keep the head precisely aligned within the 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.
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.
HP Half-Height LTO drive in an enclosure for desktop use
Current Compliance-Verified licensed manufacturers of LTO technology mechanisms are IBM, Hewlett-Packard, Quantum, and Tandberg Storage.[13]
HP's Dark Red LTO-2 cartridge
The colors of LTO Ultrium cartridge shells are somewhat standardized. HP is the notable exception.
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]
Contents[hide] |
[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.
[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
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.
- Uses the same data compression as AIT
- Tape encoding is RLL 1,7
- Bit density is low, compared to second and third generations.
- 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]
[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 non-computer definitions for bytes capacities.
- The units in this section are as follows:
- B = byte(s) = 8 bits
- KB = kilobyte(s) = 103 bytes
- MB = megabyte(s) = 106 bytes
- GB = gigabyte(s) = 109 bytes
- TB = terabyte(s) = 1012 bytes
- m = meter(s)
- mm = millimeter(s) = 1 m / 1,000
- um = micrometer(s) = 1 m / 1,000,000
- 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] Technical features
[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. This is the same as the method described by Sony in their AIT-3 specification. It used the algorithm ALDC[10] which is a variation of LZS. In addition, LTO-DC is designed so that it does not apply the compression to uncompressible data (i.e. data that is already compressed or sufficiently random to defeat the compression algorithm). LZS is a patent-encumbered algorithm, controlled by Hi/Fn.[11]LTO-DC achieves an approximately 2:1 compression ratio when applied to the Calgary Corpus. This is inferior to slower algorithms such as bzip2, but similar to 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 compression was attempted. This expansion on tape is prevented by the LTO tape drive's detection of uncompressible data.
[edit] Positioning times
Maximum rewind time is 98 seconds. 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.Average tape seek/filemark search time is 75 seconds.
[edit] Reliability
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.[edit] Tape durability
Estimated- 1.2 million passes (NOTE: many passes are required to fill up a tape)
- 30 years of archival storage
- 20000 loads and unloads
[edit] Tape layout
LTO Ultrium tape is laid out with 4 data bands sandwiched between 5 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.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.
The servo bands are used to keep the head precisely aligned within the 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.
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] 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[12] 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] Mechanisms
[edit] Cartridges
Compliance-Verified licensed manufacturers of LTO technology media are Maxell, TDK, Imation, EMTEC, Fujifilm, and Sony.[13] All other brands of media are manufactured by these companies under contract. Since its bankruptcy in 2003, EMTEC no longer makes LTO media products. Verbatim[14] and Quantegy[15] both licensed LTO technology, but never produced compliance-verified media.[edit] Colors
| 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] Sales figures
| Year | Drives sold |
|---|---|
| 2002 | 175,000 |
| 2003 | 262,000 |
| 2004 | 354,000 |
| 2005 | 461,000 |
- In September 2006, the LTO consortium announced[16] that over 1.5 million LTO drives and 50 million LTO cartridges have shipped.
- In 2005, the LTO Program reached the milestone of more than 1 million tape drives shipped and more than 30 million tape cartridges shipped since September 2000, when products based on the format first became commercially available.
- In July 2003, LTO Program announced 350,000 drives sold and 10 million cartridges sold since September 2000 (date first available).
- in 2002 LTO outships SDLT by nearly 2 to 1. Sales since then have dominated other "super" formats (SDLT, SAIT).
- Some sales data from Freeman Reports and the LTO consortium.
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