One of the most significant of the new formats is the next generation of Digital Linear Tape (DLT), otherwise known as Super DLT. This is important because developer Quantum accounted for around 80% of the tape drive market by early 1999. Drives based on Super DLT technology will far exceed the 35GB native capacity of the DLTtape IV format – with which it aims to be backwards compatible.
Using a combination of optical and magnetic recording techniques known as Laser Guided Magnetic Recording (LGMR) Super DLT uses lasers to more precisely align the recording heads. At the core of LGMR is an optically assisted servo system referred to as Pivoting Optical Servo (POS). This combines high-density magnetic read/write data recording with laser servo guiding. Designed for high duty cycle applications, the POS has a much lower sensitivity to external influences, which allows a much track density than is possible with other tape systems. The POS system decreases manufacturing costs and increases user convenience by eliminating the need for preformatting the tape. Furthermore, 10-20% more capacity is gained by deploying the optical servo on the unused backside of the media, making the entire recording surface available for actual data.
As the media moves through the POS, the optical tracking laser follows along on the backside of the media, tracking the embedded optical targets. The POS assembly pivots around a single mounting point to keep the magnetic read/write heads aligned with the optical tracks and reading data from or writing data to the tape. Another technological advance is the application of an advanced form of the Partial Response Maximum Likelihood (PRML) – a technique more usually associated with hard disk drives – to linear tape technology. This both further increases capacity and boosts data transfer rates by providing high encoding efficiency recording densities.
As indicated by the following table, the ultimate goal is to cram up to 1.2TB of uncompressed data onto a single cartridge with transfer rates rising to an eventual 100MBps uncompressed. Initial products, however, offer a more modest 110GB with sustained data transfer rates of 11MBps in native mode:
| SDLT
220 |
SDLT
320 |
SDLT
640 |
SDLT
1280 |
SDLT
2400 |
|
|---|---|---|---|---|---|
| Native Capacity | 110GB | 160GB | 320GB | 640GB | 1.2TB |
| Compressed Capacity
(2:1 compression) |
220GB | 320GB | 640GB | 1.28TB | 2.4TB |
| Native DTR | 11MBps | 16MBps | 32MBps | 50+MBps | 100+MBps |
| Compressed DTR | 22MBps | 32MBps | 64MBps | 100+MBps | 200+MBps |
| Media | SDLT I | SDLT I | SDLT II | SDLT III | SDLT IV |
| Interfaces | Ultra2 SCSI
LVD HVD |
Ultra2 SCSI
Ultra160 SCSI |
Ultra 320 SCSI
Fibre channel |
TBD | TBD |
| Date | Q1 2001 | Q1 2002 | Q3 2003 | Q1 2005 | Q3 2006 |