The Quarter-Inch Cartridge (QIC) tape format has been around for years. In fact, QIC cartridges come in two cartridge sizes, each of which hosts a large number of encoding variants. The two cartridge sizes are 4x5x0.625-inch and 3.25x2.5x0.6-inch. QIC tape model numbers begin in either DC or MC. The DC tapes use the larger form factor, whereas the MC tapes use the smaller one.
The first QIC tape standard, QIC-02, used a proprietary interface card, for which Linux drivers exist in the standard kernel. Most subsequent forms used the SCSI or floppy interfaces, with the larger form factor designs generally favoring SCSI interfaces and the smaller ones using floppy interfaces.
Two of the most popular QIC tape formats in the mid-1990s were QIC-40 and QIC-80. These two formats stored 40MB and 80MB of data per tape, respectively, although longer tapes could increase those values by 50%. These drives were popular because they were affordable to home users. By today's standards, these drives and their immediate successors are woefully short on capacity, but the most modern MC QIC formats can store several gigabytes of data. As a general rule, MC QIC drives can read from lower-capacity MC QIC tapes, but the capability of a drive to write to a lower-capacity tape varies. Like floppy disks, most MC QIC tapes require formatting by appropriate software before they can be used. The Ftape package includes a tape-formatting utility.
The DC drives have traditionally stored more data per tape than their MC cousins, which is not surprising given the physically larger size of the media. The largest DC drives can store a respectable 25GB uncompressed. Like MC drives, DC drives can usually read from lower-capacity tapes. Write capability varies, but is generally better than that of MC drives. Most DC tapes come preformatted, and don't need any special attention before being used.
Although still competitive in terms of capacity, QIC drives have fallen out of favor in recent years. Instead, Travan drives have taken over the low-end and mid-range market, whereas DAT,
DLT, and others compete in the mid-range and high ends. Nonetheless, if you have a QIC drive 8
that's adequate to your needs, or if you can buy one at a good price, there's no reason to avoid doing so, except perhaps for a scarcity of media. A
3M (now Imation; http://www.imation.com) developed its Travan technology as a proprietary P
offshoot of QIC drives. Most Travan drives aren't manufactured by Imation, though; they're made by other companies. Imation dominates the market for blank Travan media, however. Travan drives and media come in several variants:
• TR-1 The first Travan format stores 400MB of data, uncompressed. These drives generally use floppy-based interfaces.
• TR-2 This improved Travan version stores 800MB uncompressed. Most TR-2 drives use the floppy interface.
• TR-3 TR-3 doubles the capacity again, to 1.6GB uncompressed. These drives continue to use the floppy interface.
• TR-4 TR-4 represents a more substantial improvement in capacity, to 4GB. Most manufacturers switched from floppy interfaces to ATAPI and SCSI interfaces with their TR-4 models.
• TR-5 TR-5 increases the capacity to 10GB uncompressed. TR-5 drives use ATAPI or SCSI interfaces.
• NS-8 NS-8 is the name given to TR-4 drives that include built-in compression. These drives also support read-after-write operation (which I describe later in this chapter, in the section "Read-After-Write Verification"). Most NS-8 drives use SCSI interfaces.
• NS-20 NS-20 is the compressed variant of TR-5. Like NS-8 drives, NS-20 drives generally use the SCSI interface and support read-after-write verification.
NS-8 drives use TR-4 tapes, and NS-20 drives use TR-5 tapes. Some tapes are marketed for one line or another, but marketing aside, there's no difference between TR- and NS- tapes.
In addition to these versions, a few companies offer nonstandard Travan-like drives. These drives have peculiar capacities, such as 5GB. The media for these drives often look just like ordinary Travan media, but they're incompatible. I recommend sticking with a standard Travan format, in order to increase your choice in media.
Unfortunately, most Travan drives cannot write to lower-capacity Travan media, although they can usually read lower-capacity media. This fact can make upgrading a Travan drive difficult, because you must replace the (expensive) media along with the drive.
Modern Travan drives generally use the EIDE or SCSI ports on your system, but a few models use unusual interfaces, such as the parallel port or even the USB port. It's best to stick with the EIDE or SCSI interfaces.
As a general rule, Travan drives are inexpensive ($200-$500 for TR-4 or TR-5 drives in early 2000, for example), but the media are costly ($20-$40 for TR-4 or TR-5 tapes). This fact makes Travan drives an economically good choice if you expect to purchase few tapes, but if you expect to buy many tapes, you might want to consider DAT instead.
Travan drives have a reputation for noise; they make a loud whirring sound, not unlike that of a dentist's drill, when in operation. Because the tapes spin at such high speed, they also tend to generate a substantial amount of heat, so you should place the drives away from other heat-generating components whenever possible, to avoid exacerbating heat stresses on all components.
Digital Audio Tape is a tape format that was developed for the storage of audio data, but that's been adapted for use as a computer data storage medium. DAT cartridges are physically
smaller than QIC or Travan cartridges, but they store a lot of data. This feat is accomplished, in part, by the use of more advanced head technology. QIC and Travan drives record data in a handful of linear tracks on the drive. A DAT drive's read/write head resembles that of a VCR— it's tilted at an angle and spins, so that the data tracks cut crosswise. This recording method is known as helical scan recording (see Figure 8.3 for a comparison of these data storage methods). DAT drives also use a different encoding method than do linear drives like QIC and Travan devices. This more advanced design allows more data to be stored per square inch on a DAT tape than on a QIC or Travan tape, all other things being equal.
Linear tape technology:
Linear tape technology:
The rotating DAT head design yields a more efficient data storage pattern on the tape.
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