There are a large number of tape formats and it is hard to keep track of them all, especially with their different generations. This Techworld article is one of a series that will describe many of them and enable you to better compare an AIT tape drive, say, against an LTO or SDLT one. We start at the entry level with details of the QIC and DAT/DDS tape formats and include some road map details.
Old entry level. This is a long-lived ¼ inch catridge (QIC) tape format with serpentine recording. There is one head, which reads or writes a track at a time. Tracks are parallel to the tape. If a file is on track 3 then the head must read all of track 1 and track 2 before starting track 3. It is not the fastest of formats. Traditional suppliers were HP and Seagate and Imation, for example, supplied media. A current drive supplier is Seagate's tape division, now called Certance, with its TapeStor brand. Some examples of the format are:
|Raw Transfer Rate||c60MB/min||–||1MB/sec|
|Compressed Transfer Rate||c120MB/min||–||2MB/sec|
|Notes||IDE, SCSI-2 and USB||IDE||IDE. Overland's VR2 technology.|
Veteran entry level tapes for the embedded PC/server tape drive market. This is a 4mm helical scan technology based on digital audio tape (DAT), named digital data storage (DDS) and supplied by Sony, Seagate and HP. Sony owned most of the intellectual property with HP owning the rest. After the fourth generation Sony withdrew and promoted its own Advanced Intelligent Tape (AIT) format instead. Seagate and HP devised a follow-on fifth generation, called DAT-72, and there is a roadmap for the future. DAT-72 is backwards read-compatible with DDS-3 and DDS-4 cartridges, which helps users of those formats upgrade to DAT-72.
The DDS market is the largest installed tape customer base in terms of drives; DDS represents approximately half the total tape units shipped worldwide, according to the Gartner 2002 Tape Drives Market Report, published in 2002.
According to some suppliers, the DDS market is in decline and several formats are positioned as replacements, for example, Sony’s AIT-1 and Quantum’s VS 80. Exabyte’s VXA is also aimed at this part of the tape market. HP and Seagate’s tape division, now called Certance, don’t agree.
|Raw Transfer Rate||c720KB/sec||1.5MB/sec||3MB/sec||3MB/sec|
|Compressed Transfer Rate||c1.4MB/sec||3MB/sec||6MB/sec||6MB/sec|
|Notes||120m tape||125m tape. Better error resistance||150m tape. Reads and writes DDS-2 and 3.||170m tape. Thinner tracks. Sealed chamber. reads and writes DDS-4 and 3.|
More information about the DAT standard and its future roadmap can be found on the DAT website at www.DATMGM.com.
The DDS roadmap has a further two generations outlined. These may be called DAT-140 and DAT-240. Potential capacities, transfer rates and availability are:
|Raw Transfer Rate||5MB/sec||8MB/sec|
|Compressed Transfer Rate||10MB/sec||16MB/sec|
Future documents will describe ADR, SLR, DLT, SDLT, AIT, S-AIT, VXA, LTO and IBM and StorageTek formats.