Hal is a hardware engineer who sometimes programs. He is the former editor of DTACK Grounded, and can be contacted at halwh@ddj.com.
In general, there are three kinds of tape backups: the ones made by system administrators for servers on your office network, those you make on your PC, and the ones you should make on your PC, but don't. The first of these doesn't cost you any money, time, or effort, so you probably don't care whether or not MIS uses digital audio tape (DAT), linear DAT, or whatever.
Like many of you, I bought my first tape backup three years ago. (The December 7, 1993 PC Magazine included a full-page Colorado Memory Systems ad that urged readers to stop using floppy disks for backup!) But hard-disk capacities have gone up by a factor of 8 in that time, so you probably have a 120/250-MB tape backup but are using a 2.5-GB hard drive.
The problem has two solutions. One is to buy a new tape drive (and new media). This may cost a lot less than you think. The second solutionavailable to anyone currently using 2120, 2120XL, or 3020XL tape cartridgesis to upgrade to a longer tape with a lot more capacity.
Tape systems (drive, minicartridge, and format) are rated for both native (uncompressed) and compressed capacity. By a gentlemen's agreement among manufacturers, the rated compressed capacity is roughly double the native capacity. If only one capacity is mentioned in an ad, it is the compressed capacity. The actual compressed capacity is file-type dependent, but most folk find they can store at least 1.6 times the native capacity using compression.
I just bought a 3.2-GB tape-backup drive. This tells me the native capacity is 1.6 GB and that I can probably store at least 2.56 GB using compression. For the purposes of this column, I'll give capacity as native/compressed (rated); for instance "120/250 MB."
If you thumb through ads in the most recent Computer Shopper, you'll find a dizzying variety of tape drives, formats, media, capacities, and price points. Rather than review a few particular drives, I'll try to help you make sense of this variety.
Since we have banished expensive DAT drives to the outer darkness, there are only two kinds of tape available550 Oe (Oersteds) tape rated at up to 15K flux transitions per inch (FTPI, a.k.a. flux reversals per inch, or FRPI), and 900 Oe tape rated at up to 45K FPTI. In general, 1 flux transition = 1 bit, except that data bits require extra formatting overhead.
Minicartridge tapes are either 0.315 inches (8 mm) wide or 0.25 inches wide.
There are three basic types of minicartridges: QIC using 0.25-inch wide tape, QIC-W using 0.315-inch wide tape, and the Travan using 0.315-inch (8-mm) wide tape.
QIC is short for "Quarter-Inch Committee," and QIC-W for "Quarter-Inch Committee Wide." Travan is a newer standard set by a consortium of tape-backup suppliers to provide a longer tape for higher data capacity, while remaining compatible with QIC-W.
Each of the two kinds of tape (550 or 900 Oe) comes in two basic formats. The higher format has twice the data density of the lower format. QIC-W and Travan tapes have 25 percent more tracks than 0.25-inch tapes because the tapes are 25 percent wider; technically, these are different formats.
550 Oe 0.25-inch tape uses either QIC-40 ("Thetamat") or QIC-80 ("Ximat") formats. The first uses 20 tracks and 10K FTPI for 60/120 MB on a 307-foot tape; the second, 28 tracks and about 14.7K FTPI for 125/250 MB on a 307-foot tape. The QIC-40 format is obsolete. 900 Oe 0.25-inch tape uses either the 3010 ("Pimat") or 3020 ("Taumat") format. Both use 40 tracks. 3010 uses about 22.125K FTPI, 3020 about 44.25K FTPI.
Tapes are recorded in a serpentine fashion. The first track is recorded from the start of the tape to the end; tape motion is then reversed and the second track is written in the reverse direction.
Why use the lower-density format on a given tape cartridge? So you can use a tape drive that has a cheaper read/write head. The r/w head is the most expensive part of a high-density tape drive. Why use the higher density? You can store twice as much data on a given tape cartridge, lowering your media costs. My advice is to go for the higher density.
These tapes are 750 feet long and 0.315 inch wide. Tr-1 uses 550 Oe media and is roughly equivalent to the QIC-80 format. Tr-2 and Tr-3 use 900 Oe media and are equivalent to the QIC-W (3010 and 3020) formats. The Tr-4 is for DAT drives.
Travan tapes are a standardized way to cram a lot of tape (0.315 inchx750 feet) into a single cartridge, while retaining the ability to read QIC and QIC-W tapes.
Tr-1EX and Tr-3EX tapes, presumably 1000-feet long, have just been introduced.
0.25-inch tape is available in 205-, 307-, 400-, and 1000-foot lengths. 0.315-inch tape is available in 400- and 1000-foot lengths, plus the 750-foot Travan cartridges.
The new 2120EX(tra) and 3020EX tape cartridges are recent developments by Verbatim. The 400-foot tape length of a 2120XL cartridge is determined by the width of the two side-by-side tape bobbins in the cartridge. Verbatim's 2120EX cartridges hold 1000 feet by using larger bobbins that are staggered, not side-by-side. The physical cartridge is a heck of a lot longer than a standard 2120, but the height and width are unchanged.
Verbatim's 3020EX is to the 3020XL as the 2120EX is to the 2120.
Travan modifies the size and shape of the cartridge to hold more tape; the "neck" of the cartridge is the same as a QIC cartridge, but the part that remains outside the tape drive is slightly larger in all three dimensions. (Although the lengths and widths of the Tr-1 and 2120EX cartridges differ, the area of the enclosed tape is about the same, thus the capacities are the same.)
If you have a 120/250- or 680/1360-MB tape drive, it can use the newer cartridges with longer tapes if you update the software.
The Verbatim 2120EX and 3020EX tapes come with Arcada Backup 5.0 for Windows 3.1/95 on a 3.5-inch floppy, plus a 24-page manual. You can record 400/800 MB on your old 120/250-MB drive or 1.6/3.2 GB on your old 680/1320-MB drive! (A four-page info card tells you where to write for free DOS-compatible software.)
Most tape cartridges are sold with preformatted media. A 3000XL cartridge is unformatted; you can format it as either a 3010XL or 3020XL cartridge (with the right tape drive and software).
If you have only one computer, internal tape drives are usually cheaper. If you have more than one computer (or if you don't have another available front-panel slot) an external drive will be best.
All tape-backup drives are slow. You are definitely not going to sit in front of your computer waiting for completion of a full backup/verify. With hard-disk capacities of 850 MB and up, you can perform an incremental backup/verify over lunch, but a full backup/verify should be considered an overnight operation. (An incremental backup is a backup of only those files more recent than the last backup. Incremental backups, plus the occasional full backup, are a way to provide frequent backups without going broke buying tape cartridges.)
You should always verify after backing up, even though this doubles the elapsed time.
Some tape drives, such as my old Trakker 250, are noisy. Close a door between your bedroom and your computer. No door? Make sure you buy a quiet drive.
The backup time depends mostly on how fast data is recorded onto the tape. The data rates are standardized: 500 Kbits, 1 Mbit, or 2 Mbits/sec.
If you have an internal drive that uses the floppy controller, you're limited to 500 Kbits unless your floppy controller is 2.88-MB compatible, in which case 1-Mbit data rates are available. To provide the 2-Mbit/sec data rates of which 3020 and Tr-3 tapes are capable, you need a special controller card. Special controller cards usually include a data buffer that allows continuous recording. Absent that buffer, there will be pauses while software builds the next block of data to be recorded.
External drives use the parallel port. An ordinary unidirectional printer port is limited to 500 Kbits/sec. If bidirectional, 1 Mbit/sec. The newer EPP/ECP printer ports are compatible with 2-Mbit/sec data rates (or even-faster data rates when new tapes and drives permit).
SCSI tape drives are usually too expensive to be considered for personal use and hence are excluded from this article.
A 500-Kbit/sec rate results in 2.5-MB/ minute native-formatted data recording if your interface has a buffer, or (roughly) 1.8 MB/minute without a buffer. 1 Mbit/sec = 5-MB/minute native throughput with a buffer or 3.6-MB/minute without; 2 Mbit/sec doubles the 1-Mbit/sec numbers. Using compression can (up to) double the native data rate.
The maximum bit rate depends on the media and format: QIC-80, 3010, Tr-1, and Tr-2 tapes are limited to 1 Mbit/sec, while 3020 and Tr-3 tapes are capable of 2 Mbit/sec. Slower data rates are possible to accommodate nonoptimum interfaces; most (all?) manufacturer's software/hardware packages allow using the next-lower bit rate when nonoptimum interfaces are involved.
If you're using compression on your hard disk, remember that the "native" data is the uncompressed data. Plus, it may take a lot longer to uncompress the files on the hard disk and then recompress them for the tape drive.
I recently bought a new Exabyte Eagle 96 internal tape drive, locally on sale at Fry's, for a munificent $119.95 plus tax. When I opened the box I found the drive (which fits a standard 5.25-inch slot), a 2-Mbit/sec controller card with buffer and connecting cable, and an apparently complete Arcada Backup software package for DOS, Windows 3.1, and Windows 95. It didn't come with a tape cartridge.
The Eagle 96 uses 0.25-inch tapes and records 680/1360 MB on a 3020XL, or 1.6/3.2 GB on a 3020EX. It will read old QIC-80 tapes. I've seen this drive advertised at another local retail outlet for $153.00 and in the May 1996 Computer Shopper for $172.00.
3020EX cartridges are available via mail order for under $25.00. That means my media costs are just under a penny per megabyte using compression.
Perhaps half of tape minicartridge sales coincide with the purchase of the tape drive itself. Since shipments of 120/250-MB drives are almost nil, shipments of 2120 tapes are also down, and there may be lots of 2120s gathering dust on manufacturer's shelves.
I've seen sales of name-brand 2120 tapes at $0.00 (!) (after mail-in rebate) and also at $3.98 with no mail-in rebate. If you hold your hard-disk partitions to the capacity of one of these tapes, this is another cheap way to store data without buying a new tape drive.
If you buy a new tape drive, the tapes with which it is compatible will be prominently printed on the outside of the box. Here's what you'll find:
The tape-backup market is unsettled to say the least, with new models appearing in rapid succession. Like hard drives, anything you buy this year will be obsolescent and overpriced next year. The problem is, you need to back up your hard drive now.
Tape drives and cartridges are considered accessories and are subject to large retail markups (my $120 drive apparently has an MSRP of $235). You should shop around and watch for sales unless you like to pay high prices.
The information in this column and in Table 1 should help you choose among the large variety of competing tape backups.
Classification/Width/Media Tape Length Native/Compressed Capacity
2000 205' 80/160 MB
QIC-80/0.25"/550 Oe 2120 307' 120/250 MB
2120XL 400' 175/350 MB
2120EX 1000' 400/800 MB
3010XL 400' 340/680 MB
QIC/0.25"/900 Oe 3020XL 400' 680/1360 MB
3020EX 1000' 1.6/3.2 GB
QIC-W/0.315"/550 Oe 5122F 400' 208/420 MB
3010XLF 400' 420/850 MB
QIC-W/0.315"/900 Oe 3020XLF 400' 850/1700 MB
Travan/0.315"/550 Oe Tr-1 750' 400/800 MB
Tr-1EX 1000'* 500/1000 MB
Tr-2 750' 800/1600 MB
Travan/0.315"/900 Oe Tr-3 750' 1.6/3.2 GB
Tr-3EX 1000'* 2.2/4.4 GB