Linear Tape-Open
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Image:LTODriveWithTape.jpg Linear Tape-Open (or LTO) is a computer storage magnetic tape format developed as an open alternative to the proprietary Digital Linear Tape (DLT). The format was developed and initiated by Certance, Hewlett-Packard, and IBM. An implementation of the LTO tape format goes by the name "Ultrium".
Current manufacturers of LTO tape drives are IBM, Hewlett-Packard, Certance (acquired by Quantum in 2005), NEC, Seagate, Qualstar, Exabyte and Tandberg Data.
LTO Ultrium manufacturers: IBM StorageSmart, Seagate Viper, HP SureStore, Dell
Contents |
Overview
| Format | Date | Capacity (GB) - with 2:1 compression | Speed (MB/s) - with 2:1 compression | WORM availability |
|---|---|---|---|---|
| LTO1 | 1999 | 100 - 200 | 20 - 40 | No |
| LTO2 | 2002 | 200 - 400 | 40 - 80 | No |
| LTO3 | 2005 | 400 - 800 | 80 - 160 | Yes |
| LTO4 | TBA (2006) | 800 - 1600 | 120 - 240 | Yes |
| LTO5 | TBA (2008) | 1600 - 3200 | 180 - 360 | Yes |
| LTO6 | TBA (2010) | 3200 - 6400 | 270 - 540 | Yes |
Factual Notes
LTO originally came in two varients Accelis and Ultrium
- Ultrium -- The high capacity variant
- Accelis -- The high speed variant
Accelis was developed in 1997 to meet customer demands for fast access to data by using a two-reel cartridge that loads in the middle of the tape to minimize access time. However, the performance never exceeded that of the Ultrium tape format so there was never a demand for Accelis. So LTO came to mean the same as Ultrium.
The LTO-1 (Ultrium-1) tape format was a quick to market design with a strong view to the future, it is required that:
- 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.
Because it was quick to market the original LTO-1 was created using easy technology.
- Uses the same data compression as AIT
- Tape encoding is RLL 1,7
- Bit density is low.
- The cartridge is fairly large at 102.0 x 105.4 x 21.5 (mm)
| LTO-1 | LTO-2 | LTO-3 | |
|---|---|---|---|
| Tape Width | 12.65mm | 12.65mm | 12.65mm |
| Tape Thickness | 8um | 8um | 8.9um |
| Tape Length | 680m | 680m | 609m |
| Tape Tracks | 384 | 512 | 704 |
| Encoding | RLL 1,7 | PRML | PRML |
| Data Rate | 10..20Mb/s | 20..40Mb/s | 40..80Mb/s |
- Tape speed adjusts to available stream speed.
Logical format.
The tapes use a compression method labeled LTO-DC this is the same as the Sony AIT-3 algorithm ALDC which is a variation of LZS and LZ77 tuned to work with very compressible data (Like MS-Word documents and BMP images). In addition LTO is configured so that it does not apply the compression to uncompressable data, ie data that is already compressed or is encrypted.
| The Calgary Corpus | |
| Compression method | Compressed size |
|---|---|
| None | 3251493 |
| lzop | 1592692 |
| AIT-3 | 1558353 |
| LTO-2 | 1558353 |
| ncompress -b13 | 1510478 |
| DLT | 1479577 |
| ncompress | 1367363 |
| gzip -6 | 1068037 |
| bzip2 -9 | 890079 |
The tapes contain a strong error correction algorithm that makes data recovery possible when lost data is within one track or up to 32mm of the tape medium.
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.
Tape layout
Tape layout has 4 data bands numbered 3,1,0,2 across the tape. The bands are filled in numeric order so the edge of the tape is used last. Each band has servo tracks above and below the data. Tracks are written in passes, each pass writes 8 tracks using 8 heads. Alternate sets of tracks are written in opposite directions (like QIC). The 8 heads are spaced two tracks apart so that two tracks written in the forward direction are separated by one in the reverse.
Estimated durability
- 1 million passes,
- 30 years of archival storage,
- 20000 loads and unloads.
Maximum rewind time 98 seconds. Note due to the back and forth writing this rewind time is reached at fairly low utilisations and is essentially random after that.
Average tape seek/filemark search time 75 seconds.
LTO-CM
The cartridge has internal EEPROM of 4096 Bytes which uses non contacting passive RF interface for access.
WORM
New for LTO-3 is a WORM capability, normally only useful for legal record keeping, an LTO-3 drive will not erase or overwrite data on a WORM cartridge.