Storage Space

Will Bigger and Faster Mass Storage Solutions Be Enough?

Linda Boyer

Accurately predicting the mass storage capacity your company will need over the next few years is a nearly impossible task, but one thing is certain: Your company will need more than it has now. In fact, if a recent study conducted by Strategic Research Corporation (SRC) is any indication, your company will increase storage capacity 60 percent by the end of 1998. (For more information, visit SRC's World-Wide Web site at http://www.sresearch.com.)

If your company now has a capacity of 1 TB and capacity continues to expand at this rate, your company will have a capacity of more than 10 TB within the next five years. With 10 TB, which is 10 trillion bytes, your company will have enough space to store the entire printed collection of the U.S. Library of Congress.

To what storage media will your company turn to meet its growing mass storage needs? For the next few years, your company is likely to retain the storage media it uses today: hard disks, tape cartridges, and optical discs. This article examines the capacity and performance these storage media currently offer, the technologies that are evolving to increase capacity and performance, and the drives and devices available for Novell networks.

HARD DISK DRIVE TECHNOLOGIES

The value of mass storage solutions is measured primarily in terms of capacity and performance. Generally, you want the mass storage solution that offers the highest capacity and performance for the lowest cost. So how do hard disk drives fare?

Hard disk drives offer relatively high capacity, ranging anywhere from 2.1 GB to 18.2 GB at a cost of about 10 to 15 cents per megabyte. Outperforming all other mass storage solutions today, hard disk drives offer access times of less than 10 milliseconds and data transfer rates exceeding 15 MB per second. In light of the cost, capacity, and performance of hard disk drives, it's not surprising that they are the preferred solution for primary, online mass storage on distributed networks.

Hard disk drive technology is advancing faster than any other mass storage technology. Just think how much capacity has increased and size has decreased in the last forty years. In 1956, IBM Corp. introduced the Random Access Method of Accounting and Control (RAMAC) 305 computer, which included the first commercial magnetic hard disk drive. IBM's RAMAC 305 used 24-inch hard disks with such limited capacity that 50 of these hard disks were required to provide 5 MB, which equals a capacity of about 2 kilobits per square inch. In 1996, IBM released a product that delivers more than 5,000 times that capacity in one-tenth the size: IBM's TravelStar VP laptop contains two 2.5-inch hard disks that offer a total of 1.6 GB, which equals a capacity of approximately 1.44 gigabits per square inch.

The ticket to increasing capacity is squeezing more bits onto a hard disk. (A hard disk stores digital information in the form of bits, which are arranged in tracks on the magnetically coated surface of the hard disk.) The smaller the length of each bit and the smaller the width of each track, the more bits you can fit on each hard disk. This measurement--the number of bits per inch multiplied by the number of tracks per inch--is called areal density.

Hard disk drive technology increases areal density and, therefore, capacity at an amazing rate. In fact, according to Professor Mark Kryder of Carnegie Mellon's Data Storage Systems Center (DSSC), a research organization committed to improving the competitiveness of the U.S. data storage industry, areal density on hard disks is increasing by 60 percent each year. Areal density has grown at this rate since 1991, when IBM introduced the first hard disk drive with a magnetoresistive (MR) head, forever changing hard disk drive technology.

Two Heads Are Better Than One

As manufacturers increase areal density, bits and tracks get smaller, and the signals generated by magnetized spots that represent bits get weaker. To ensure that hard disk drive heads can detect these signals and thus read recorded data, manufacturers must compensate for weakening signals.

One way to ensure that these heads can detect weakening signals is to make the heads fly closer to the hard disk. However, this approach has nearly reached its limit, barring the possibility of allowing the heads to actually touch the hard disk. Heads on today's hard disk drives typically fly two to three microinches above the hard disk--a space much smaller than a dust particle.

Another method of detecting weakening signals is to improve the sensitivity of hard disk drive heads. The inductive head technology that has been used since the introduction of the first hard disk drive is rapidly being replaced by MR head technology. MR heads can deliver many times the areal density possible with inductive heads.

To understand MR head technology, you need to understand how data is stored on hard disks. As you know, computers communicate using binary code, in which all letters and numbers are represented by a series of 0s and 1s called bits. For example, the letter B is encoded as 01000010. Hard disk drive heads record data by creating magnetic patterns corresponding to the bits that represent this data.

A hard disk drive head creates these patterns by changing the direction of the magnetic poles that are in microscopic spots on the hard disk's magnetic coat. These spots, or domains, have positive and negative poles like miniature magnets.

To record data, the hard disk drive head uses an electrical current to reverse the direction of a domain's magnetic pole whenever the head encounters a 1--a process called flux reversal. For example, if the positive pole were pointing to the right and the head encountered a 1 during the recording process, the head would point the pole to the left.

To read recorded data, the hard disk drive head flies over the hard disk and, through various means, senses the transitions or lack of transitions in the domains' magnetic poles. If the head senses a transition, it decodes the transition as a 1 and, domain by domain, bit by bit, reads and decodes the magnetic patterns that represent recorded data. The more sensitive the head is to the hard disk's domains, the smaller these domains can be, thus enabling an increase in areal density.

MR heads are far more sensitive than inductive heads. Because inductive heads use a single, bulky head for both reading and writing data, their sensitivity is limited. In contrast, MR heads actually consist of two heads: an inductive head, which is optimized for writing data, and an MR head, which is optimized for reading data.

MR heads are already capable of handling an areal density of 5 gigabits per square inch and are expected to eventually handle a capacity of 10 gigabits per square inch. Inductive heads, on the other hand, can handle only 400 megabits per square inch.

An MR head is composed of an alloy film, or MR sensor, which is located between two magnetic shields. These shields limit the MR head's region of sensitivity, preventing the MR head from sensing magnetic fields that might stray from domains on other tracks (and thus possibly corrupt the interpretation of recorded data). The electrical resistance of the MR sensor changes slightly when the MR head flies over the hard disk's domains.

A precision amplifier in the MR head measures the MR sensor's change in resistance--a measurement that increases or decreases depending on the direction of the magnetic poles. The precision amplifier then generates an analog signal based on the measurement and relays the signal to the hard disk drive's read channel. In this read channel, the signal is translated into a series of 0s and 1s representing the bits that comprise the recorded data.

Hard disk drive manufacturers, such as Quantum Corp., Seagate Technology Inc., and IBM, have contributed to the evolution of MR head technology, and these manufacturers use MR heads in most, if not all, of their hard disk drives. (See "Hard Disk Drive Products.") For example, Seagate Technology, which designed the now industry-standard MR read-write head configuration, uses MR heads in its Hawk, Barracuda, and Cheetah hard disk drives. In fact, Seagate Technology will incorporate MR heads in all of its hard disk drives by the end of 1997.

Quantum introduced hard disk drives with MR heads in 1994 and has continued to develop drives with MR heads, including the Atlas and Viking drives.

IBM, however, has clearly spearheaded MR head technology. As mentioned earlier, IBM demonstrated the first MR head in 1991. IBM now uses MR heads in all of its hard disk drives. This year, IBM demonstrated an MR head recording 5 gigabits per square inch, which is the equivalent of recording every word from 625 300-page novels in one square inch. At this areal density, each bit is 47-by-4 millionths of an inch--small enough that 1,000 of these bits could span the diameter of a human hair.

IBM also invented the next evolution of MR head technology: the spin-valve head. Spin-valve heads, which should extend the use of MR head technology into the 21st century, are more sensitive than MR heads: Spin-valve heads can read hard disks with an areal density that is greater than 5 gigabits per square inch.

Partial Response, Maximum Likelihood

Although improving MR heads can increase capacity, areal density increases dramatically when MR head technology is combined with partial-response-maximum-likelihood (PRML) technology. PRML technology ensures highly accurate readings of the analog signals generated by a hard disk drive head.

When a read channel receives an analog signal, the channel analyzes this signal to determine the high (positive) peaks and the low (negative) peaks, decoding these peaks into 0s and 1s. As areal density increases, the peaks in the analog signal begin to overlap. The traditional use of peak detection, which analyzes individual peaks in an analog signal, does not work well when these peaks overlap.

Rather than analyzing individual peaks in the analog signal, the PRML read channel samples points throughout this signal and then uses complex algorithms to determine the most likely position of each peak. As a result, the PRML read channel reduces the possibility of error when peaks overlap. Not surprisingly, hard disk drive manufacturers such as IBM, Quantum, and Seagate Technology use PRML read channels in many of their hard disk drives. (See "Hard Disk Drive Products.")

Like MR head technology, PRML technology may be used well into the 21st century, by which point hard disk drive manufacturers should be demonstrating hard disk drives with an areal density approaching 50 gigabits per square inch. However, every technology has its limits, and these technologies are no exception.

MR head technology and PRML technology are expected to reach their limit when hard disk drives achieve an areal density of 50 to 100 gigabits per square inch. At that point, says Professor Kryder, "we have concerns about the superparamagnetic effect." The superparamagnetic effect refers to a point at which the magnetic fields on a hard disk cannot remain stable at room temperature. However, hard disk drive manufacturers are nearly a decade away from encountering the superparamagnetic effect and will probably invent other technologies to counter this effect.

When One Hard Disk Drive Won't Do

Every storage medium has a sibling technology that enables you to incorporate multiple units with one device to increase capacity and improve performance. For example, you can place multiple tape drives and cartridges into a tape library, which can store terabytes of data. Similarly, CD-ROM jukeboxes can store terabytes of data using multiple optical drives and disks. (Tape libraries and CD-ROM jukeboxes will be discussed in more depth later in this article.) The sibling technology for hard disk drives is Redundant Array of Independent Disks (RAID).

RAID systems are generally known for providing fault tolerance. To provide this fault tolerance, RAID systems include two or more hard disk drives in one device, thereby increasing capacity. RAID systems also improve performance by enabling you to perform several read-write operations simultaneously.

RAID systems are based on different architectures, or levels, that offer various degrees of performance and fault tolerance. Low-level RAID systems provide data redundancy by ensuring that a copy, or mirror, of the data set exists for each hard disk in the array. Higher-level RAID systems, on the other hand, provide data redundancy using parity checking, which ensures that every byte of data contains either an odd or even number of 1s by adding an extra bit to each byte. If one bit of data is incorrect, the parity changes, signaling an error.

RAID levels 3 through 5 maintain a copy of all of the data stored in the array. In addition, RAID levels 3 through 5 store parity data, which is the version of the data that includes the extra bits. Depending on the RAID level, this parity data is either distributed across every hard disk in the array or stored on the parity disk. RAID systems use parity data to mathematically recreate lost data.

Several manufacturers offer RAID systems that are compatible with IntranetWare, NetWare 4, and NetWare 3, including nStor Corp., RaidTec Corp., and StreamLogic Inc. For example, nStor's CR8e has eight bays that support hard disk drives with a capacity of 4 to 9 GB, thus providing a possible total of 72 GB of storage space. RaidTec's FlexArray product family supports two to seven hard disk drives, offering up to 63 GB of storage space. In addition, the FlexArray products support hard disk drives from manufacturers such as IBM, Seagate, and Quantum.

TAPE DRIVE TECHNOLOGIES

Whether you use a single hard disk drive or a RAID system, the performance of hard disk drives is unbeatable, which is one of the reasons that hard disk drives have a corner on the online storage market. However, tape drives rule the offline storage market because tape drives run tape cartridges, which are low-cost, high-capacity media capable of storing anywhere from 5 to 35 GB of uncompressed data per cartridge. Unfortunately, tape drives offer a relatively slow transfer rate, ranging from 300 KB/s to 5 MB/s of uncompressed data, restricting the practical use of tape solutions to offline (and occasionally nearline) storage.

The low cost of tape drives makes up for their performance limitations and contributes to their popularity as a mass storage solution for backup and archival purposes. Tape drives can cost as little as U.S. $526 for a 2 to 4 GB 4mm digital audio tape (DAT) drive and as much as U.S. $7,500 for a 35 GB digital linear tape (DLT) drive.

These prices may seem high, but few network administrators purchase a tape drive to use with only one tape cartridge. When you amortize the cost of a tape drive over several tape cartridges, which cost from U.S. $7 for a 4mm DAT cartridge to U.S. $33 for a 10 GB DLT cartridge, the tape drive becomes much less expensive. For example, one 4mm DAT drive costing U.S. $526 and 10 4 GB DAT cartridges costing U.S. $7 each could store 40 GB of data--as much information as you would find on one floor of a local library--for less than a penny per megabyte.

Although many tape drive technologies exist, the most common technologies in the small- to medium-sized network market are quarter-inch cartridge (QIC), DLT, 4mm DAT, and 8mm.

The QIC Fix

Although QIC is rumored to be a dying technology, it continues to live. According to Quarter-Inch Cartridge Drive Standards Inc., an international trade association dedicated to promoting QIC technology, more than 15 million QIC tape drives were in use in 1996--more than twice the number of any other drives for removable storage media.

QIC tape drives have many advantages: For example, QIC tape drives have a migration path that promises a capacity of up to 50 GB and backward compatibility with the largest installed tape drive base in the world. (For more information about QIC, visit Quarter-Inch Cartridge Drive Standards's web site at http://www.qic.org.)

Commercialized by Imation Corp., QIC is a reliable mass storage solution that offers the following:

As a result, QIC is a staple for workstations, peer-to-peer networks, and small networks. (See "Tape Drive Products.")

QIC tape drives record data in a linear fashion, which is commonly described as a serpentine recording approach. (See Figure 1.) In a QIC tape drive, the tape passes over a stationary head, which records data down the length of the tape. When the tape drive reaches the end of the tape, the tape drive head steps to the next track and continues recording in the opposite direction, wrapping data back and forth from one end of the tape to the other. A QIC head generally has either a single channel (for reading and recording data in both directions) or two channels (one channel for each direction).

QIC tape drives are available in two sizes:

Tape cartridges for 5.25-inch QIC tape drives have as much as 1,500 feet of quarter-inch magnetic-coated tape that can store up to 13 GB of uncompressed data on as many as 144 tracks. Tandberg Data Inc. claims nearly 90 percent of the 5.25-inch QIC market, and the release of the Multichannel Linear Recording 1 (MLR1) tape drive has probably clinched Tandberg Data's market dominance.

MLR1 is a 5.25-inch QIC tape drive that provides a capacity of 13 GB, which far exceeds the capacity offered by other QIC tape drives and rivals the capacity offered by DLT tape drives. MLR technology incorporates elements of MR technology, which contribute to MLR1's increased capacity. MLR1 also provides excellent performance because the MLR1 head can write to multiple channels simultaneously. In fact, Tandberg Data anticipates that by 1999, MLR technology will allow for a capacity of 80 GB and a transfer rate of 12 MB/s.

The smaller 3.5-inch QIC tape drives are also popular. These tape drives run Travan minicartridges, which are as small as a deck of playing cards. Developed by 3M Corp. and HP Colorado (a subsidiary of Hewlett-Packard Co.), Travan minicartridges have 750 feet of .315-inch tape and provide a capacity of up to 2.5 GB.

Travan minicartridges are increasingly popular not only because of their capacity but also because of their size: Smaller tape cartridges take up less space. Travan minicartridges are used by most QIC tape drive and tape cartridge manufacturers, such as Tandberg Data and Seagate Technology.

More Storage With DLT

Although Travan minicartridges are convenient, they can't compete with the capacity of DLT cartridges, which offer up to 35 GB. Similarly, the 30 MB/m transfer rate of a 3.5-inch QIC tape drive pales in comparison with the 5 MB/s transfer rate of a DLT drive. Not surprisingly, many network administrators consider DLT to be the premier tape drive solution.

Originally developed by Digital Equipment Corp. (DEC), DLT technology is now owned by Quantum. DLT drives are available in a 5.25-inch size and run tape cartridges that hold up to 1,800 feet of .5-inch tape (twice the width of QIC tape), which allows for a track density of 416 tracks per inch. Like QIC tape drives, DLT drives use the serpentine recording approach, in which data is written to tape that moves past a stationary head. (See Figure 1.)

In addition to high capacity, DLT's claim to fame is performance. Although the 5 MB/s transfer rate of DLT drives is impressive, a tape drive's transfer rate does not necessarily reflect its throughput. If the transfer rate of a tape drive is faster than the data rate of its host system, the tape drive has to stop frequently to reposition the tape. As a result, performance--particularly in terms of throughput--suffers.

DLT technology overcomes this problem by monitoring the host system and adjusting the DLT drive's cache buffering operations to match the host system's data rate. In this way, DLT technology minimizes the performance drain that repositioning the tape can cause.

So why doesn't everyone rush out to buy a DLT drive? Perhaps because these tape drives seem expensive. Low-end DLT drives (with a capacity of 15 GB) cost approximately U.S. $2,000, and high-end DLT drives (with a capacity of 35 GB) cost nearly four times that amount. (See "Tape Drive Products.")

DLT cartridges are also relatively expensive, costing U.S. $33 for a 6 to 10 GB cartridge and U.S. $100 for a 20 to 40 GB cartridge. However, when you amortize the price of a DLT drive over several DLT cartridges, DLT provides one of the lowest cost per GB of any mass storage solution.

The migration path for DLT drives is the Symmetric Phase Recording (SPR) technology on which Quantum's DLT 7000 is based. Quantum claims that with SPR technology, DLT drives can achieve a transfer rate that exceeds 20 MB/s and DLT cartridges can provide a capacity of up to 200 GB.

The SPR format enhances traditional DLT drives by changing the angle of the tape drive head to record data on adjacent tracks. Changing this angle not only eliminates cross-track interference but also makes it possible to reduce track width and, in turn, increase capacity. The SPR format further enhances traditional DLT drives with Parallel Channel Architecture (PCA), a four-channel system that enables four channels of data to be read from or written to simultaneously.

DAT's It!

Despite DLT's high capacity and performance, DLT struggles for a substantial share of the market in which DAT is comfortably entrenched. When it comes to backing up servers on medium-sized networks, 4mm DAT drives have long been the most popular tape drive solution.

In contrast to QIC and DLT drives, which use the serpentine recording approach, 4mm DAT drives use the helical scan recording approach. (See Figure 1.) With the helical scan recording approach, 4mm DAT drives wrap data around a rotating head, writ-ing data on the tape in parallel, diagonal stripes.

4mm DAT drives are based on the digital data storage (DDS) specifications developed by the DDS Manufacturers Group, which is headed by HP and includes Seagate Technology and Sony Electronics Inc. The current specification, DDS-3, allows for 24 GB of compressed data and a transfer rate of up to 2 MB/s. 4mm DAT drives in this range typically cost about U.S. $2,000--almost twice the amount of 4mm DAT drives based on the DDS-2 specification or lower.

Sometime in 1999, you may begin seeing 4mm DAT drives based on an upcoming specification, DDS-4. These tape drives should provide a capacity of 48 GB and a transfer rate of up to 6 MB/s.

8mm--Alive and Well

Adapted from 8mm home videotape technology in the mid-1980s, 8mm tape drives meet the needs of most small- and medium-sized networks. Contrary to popular opinion, 8mm is not DAT. "It is a recurring mistake to link 8mm with DAT," explains Mark Kulaga of Exabyte Corp., "but DAT is generally used for 4mm only." 8mm tape drives were introduced to the market before 4mm DAT drives, which adopted the same helical scan recording approach that 8mm tape drives use. The common use of this recording approach may have led to the misconception that 8mm is DAT.

Today's 8mm tape drives offer a capacity of up to 20 GB for uncompressed data and a transfer rate as high as 3 MB/s. Exabyte, which pioneered 8mm technology and continues to dominate the 8mm market, expects 8mm tape drives to offer a capacity of 60 GB and a transfer rate of 12 MB/s by the turn of the century.

What 8mm tape drives lack in capacity, they compensate for in mean time between failure (MTBF) and expected head life. Exabyte says that its Eliant 820 8mm tape drive has an MTBF of 200,000 hours, compared with an MTBF of 80,000 for Quantum's more expensive DLT 4000 tape drive. Exabyte also says that the expected head life of Mammoth, its flagship product, is about 35,000 hours, compared with only 10,000 hours for the DLT 4000.

Exabyte's claims of a lengthy expected head life are aimed at dispelling a common concern about the helical scan recording approach. Because tape drives that use the helical scan recording approach wrap the tape tightly around the heads, these tape drives supposedly wear out the tape and the heads more quickly than tape drives that use the serpentine recording approach.

In fact, tape drives that use the serpentine recording approach typically have a higher MTBF than tape drives that use the helical scan recording approach. For example, Tandberg Data's 5.25-inch QIC tape drives have an MTBF as high as 300,000 hours. Nevertheless, tests conducted by the National Media Laboratory (NML) show that serpentine tape drives don't always surpass helical scanning tape drives: In its tests of Exabyte's 8505XL (an older version of Exabyte's Eliant 820), NML predicted an expected head life of up to 40,000 hours (30,000 more hours than Quantum's DLT 4000).

Autoloaders and Tape Libraries

If one QIC, DLT, DAT, or 8mm tape drive isn't enough, you can increase capacity by using an autoloader or an automated tape library. An autoloader consists of one tape drive that can automatically load as many as 12 tape cartridges. For example, Seagate Technology manufactures a DAT autoloader with 12 tape cartridges, which provide a capacity of up to 96 GB.

An automated tape library, on the other hand, consists of multiple tape drives that can automatically load hundreds of tape cartridges. For example, StorageTek's Timberwolf 9710 DLT supports ten DLT 4000 or DLT 7000 tape drives and holds up to 588 DLT cartridges, offering a capacity of 600 GB to 20.58 TB in a device that occupies less than 16 square feet.

You can purchase autoloaders and automated tape libraries for QIC, DLT, DAT, or 8mm tape drives from most tape drive manufacturers, such as Exabyte, Quantum, Tandberg Data, and Imation.

OPTICAL DRIVE TECHNOLOGIES

If hard disk drives dominate the online storage market and tape drives dominate the offline storage market, where do optical drives fit into the mass storage picture? Like tape drives, optical drives offer removable storage media with a relatively long life expectancy. Optical drives also offer respectable transfer rates--certainly better than tape drives. When you look at optical drives in that light, as Professor Kryder points out, "You could say they have the best of both worlds."

However, optical drives fall short of the performance provided by hard disk drives and are more expensive than tape drives. The performance of optical drives is limited by their massive recording heads, which can't move as quickly as hard disk drive heads. And unlike tape drives, the capacity and cost of optical drives don't always compensate for their good, but not-as-good-as-hard-disk-drives, performance. For example, Sony Electronics's CMO-R540-10 external, 5.25-inch magneto-optical (MO) drive costs U.S. $2,900 and supports 2.6 GB optical discs that cost U.S. $80. These drives seem a bit costly compared to a Quantum DLT drive that costs U.S. $2,000 and holds 15 GB DLT cartridges that cost U.S. $38.

Still, every mass storage market has its benefits, and the optical market is no exception. For example, MO drives are an ideal nearline mass storage solution for a large records-based database--the type of database an insurance company might maintain. If a customer called requesting information about a claim, you wouldn't want the database storing this information to be on a tape cartridge because it would take a minute or more to access the claim. Instead, you would want the database to be on an optical disc so that the customer would have to wait only seconds.

The optical market also comprises what is perhaps the most popular form of removable storage media: CD-ROMs.

CD-ROMs Rise Above the Pits

CD-ROMs are a storage media for which nearly everyone has a drive. In addition, CD-ROMs offer a capacity of 650 MB--the equivalent of about 450 floppy diskettes--for the relatively low cost of about 1.5 cents per megabyte.

The CD-ROMs you buy in a store have three layers: a polycarbonate substrate layer, a reflective metal layer, and a protective lacquer coating. These CD-ROMs are created from a mold for mass duplication. The mold presses microscopic pits into the polycarbonate substrate layer, which is the data layer. CD-ROM drives, in turn, read data by translating the presence or absence of these pits into 1s and 0s, respectively.

The speed with which a CD-ROM drive translates the presence or absence of pits--that is, the rate at which the drive can play back data--is designated as 1x, 2x, 4x, and so on. For example, a 1x CD-ROM drive plays back data at a rate of 150 KB/s, a 2x CD-ROM drive plays back data at a rate of 300 KB/s, and a 4x CD-ROM drive plays back data at a rate of 600 KB/s.

The fastest CD-ROM drives are 32x. Toshiba Inc.'s 32x CD-ROM drive plays back data at a rate of 4.8 MB/s--double the speed of a 16x CD-ROM drive. (See "Optical Drive Products.")

You can also use CD-ROM servers, making CD-ROM drives a good nearline mass storage solution for IntranetWare, NetWare 4, and NetWare 3. Many CD-ROM servers provide NetWare emulation, which enables these servers to appear as IntranetWare or NetWare servers in your Novell Directory Services (NDS) tree and CD-ROMs to appear as volumes. As a result, you can control users' access to a CD-ROM server and to the CD-ROMs themselves using IntranetWare or NetWare's file system security.

CD-ROM servers are available from several manufacturers, including Ornetix Network Products Inc. and Future Echo Inc.

CD-Recordable to the Rescue

Until recently, the most conspicuous drawback to CD-ROM technology was that it was not rewritable. However, CD-recordable (CD-R) technology and CD-rewritable (CD-RW) technology are now available.

As the name implies, CD-R drives allow you to create your own CD-Rs. CD-R drives record data by using a laser to burn pits onto a CD-R's organic dye layer (an extra layer that sits between the polycarbonate substrate layer and the reflective metal layer of a traditional CD-ROM). Because a CD-R is a write-once, read-many (WORM) medium, you can record data to the CD-R only once. In other words, you cannot erase the data.

CD-Rs are available in the form of 63- or 74-minute CD-Rs, which provide a capacity of 650 MB or 680 MB, respectively. CD-R drives, which designate speeds for both reading and writing data, offer a read rate as high as 8x (1,200 KB/s)--a rate these drives are not likely to surpass any time soon because a CD-R drive head makes higher speeds impossible.

However, CD-R drives generally offer a write rate of only 2x. Although the write rate is measured in the same units as the play-back rate for CD-ROM drives, this write rate refers to the speed at which the CD-R drive can write data. For example, a 2x CD-R can write data at a rate of 300 KB/s, allowing you to burn a 74-minute CD-R in a little over 30 minutes.

Not long ago, CD-R drives were vastly expensive devices (costing U.S. $25,000) designed primarily for mass production. However, because the cost has decreased considerably, manufacturers are marketing CD-R drives to network administrators. Depending on their read and write rate, CD-R drives are now available for less than U.S. $2,000, with many drives costing less than U.S. $1,000 and some drives costing as little as U.S. $500. (See "Optical Drive Products.")

CD-R drives are even more cost effective when you consider the fact that CD-R drives can read CD-ROMs. In addition, CD-Rs, which can be read by both CD-R and CD-ROM drives, usually cost approximately U.S. $5 each.

Of course, the WORM limitation of CD-Rs is not to be taken lightly. If you are nearly finished recording data on a CD-R and something goes awry, you're left with a shiny piece of plastic that's good for little else than the trash. Fortunately, the CD-R industry recognized this problem long ago and has developed a solution: CD-RW technology.

CD-Rewritable--A.K.A. CD-Erasable

CD-RW drives were called CD-Erasable drives until the end of 1996. About that time, CD-RW manufacturers began referring to these drives as CD-RW drives, purportedly because the word erase has negative connotations (as in, "What if I erase something important?").

The main difference between CD-Rs and CD-RWs is that you can erase and rewrite data multiple times on CD-RWs. The other difference is the way CD-Rs and CD-RWs store data. Instead of burning pits onto the disc (as CD-R drives do), a CD-RW drive records data by changing the material in tiny areas on this disc from a crystalline state to an amorphous state. These states are translated into 1s and 0s, respectively.

HP claims to be the first manufacturer to release a "full-function" CD-RW drive, which is called CD-Writer Plus. (See "Optical Drive Products.") This claim alludes to the fact that CD-Writer Plus is the first CD-RW drive to use the file-by-file rewrite capability as defined in the CD-universal device format (CD-UDF) specification. In September, HP began shipping CD-Writer Plus to resellers, distributors, and retailers at a cost of U.S. $499 for an internal drive and U.S. $610 for an external drive. (The suggested retail price is not yet available.)

A CD-RW is quite expensive, costing U.S. $32, compared with U.S. $5 for a CD-R. The good news is that CD-RW drives are backward compatible with both CD-Rs and CD-ROMs. However, if you use a CD-RW drive to write data onto a CD-R, the advantages of CD-RW technology are lost: You can write data only once to the CD-R.

The Next Big Thing

Digital video disc (DVD) is an evolution of its parent technology, CD. DVD technology is backed by a group of 10 companies called the DVD Forum, which includes Hitachi, Philips, Sony, and Toshiba.

The term digital video disc stems from the original focus of DVD technology, which was designed to store video data in the same way that CDs store audio data. The first DVD players were released at the end of 1996, and an estimated 600 titles will be available on DVD by the end of 1997. For example, Columbia's TriStar Home Video has already started shipping movies on DVD, including "Legends of the Fall" and "Sense and Sensibility."

However, DVD technology offers more than a great video solution. Because DVD technology supports all types of data--such as audio, video, still images, and raw data--some manufacturers use the term digital versatile disc instead.

The fact that a DVD provides seven times the capacity of a CD will undoubtedly ensure the success of DVD technology. A DVD looks like a CD and stores data in a similar manner. A DVD is comprised of two discs, which are bonded together to form one disc that is the size of a standard CD.

On both CDs and DVDs, data is represented by microscopic pits. And like CD drives, DVD drives translate the presence or absence of these pits into 1s and 0s, respectively.

DVD-ROM technology differs from CD-ROM technology by using a unique read-write approach, which allows more pits to fit onto the same size surface. As a result, a DVD can hold more data--a lot more. For example, one layer of a one-sided DVD can store 4.7 GB of data, compared with the 650 to 680 MB of data a CD can store. If you record data on the second layer, capacity reaches 9.4 GB.

DVD-ROM drives use a laser with a shorter wavelength than the laser used in CD-ROM drives, but DVD-ROMs also include special lenses to read CD-ROMs. However, some DVD-ROM drives cannot read CD-Rs because the data layer on CD-Rs doesn't properly reflect the wavelength of the DVD-ROM drives' laser. Exceptions to this rule do exist: For example, Hitachi's DVD-ROM drive can read CD-ROMs, CD-Rs, and CD-RWs.

Most manufacturers of CD-ROM drives are shipping DVD-ROM drives. (See "Optical Drive Products.") Toshiba was the first manufacturer to get a DVD-ROM drive to market, shipping its SD-M1002 in November 1996.

In addition, PCs with integrated DVD-ROM drives are now available. For example, IBM shipped its Aptiva with an integrated DVD-ROM drive in June 1997.

DVD-RAM drives are also starting to appear, despite predictions that these drives would not ship until well into 1999. DVD-RAM drives allow you to erase and rewrite data many times on DVD-RAM discs, which offer a capacity of 2.6 GB. Because DVD-RAM drives are backward compatible, they can also read CD-ROMs and read and write to CD-Rs and CD-RWs.

Hitachi shipped samples of its DVD-RAM drives in June 1997 and expects PCs with these drives to appear before the end of 1997. Werner Glinka, director of Marketing for the Storage Products Group of Hitachi America Ltd., believes there is great "potential for rewritable DVD products to become the computer industry's preferred device for removable storage in home and business environments."

CD-ROM Towers and Jukeboxes

With seven times the capacity of a CD-ROM drive for as little as U.S. $500, a DVD-ROM drive is a convenient and cost-effective alternative--instead of requiring six CD-ROMs to store the data in all of the U.S. white page directories, you would need only one DVD-ROM.

The only optical devices that can compete with the capacity of a DVD-ROM drive are a CD-ROM tower or a CD jukebox. A CD-ROM tower holds several CD-ROM drives, enabling users on your company's network to share centrally located CD-ROM drives. For example, TAC Systems Inc.'s LAN Mini, which holds seven CD-ROM drives, connects directly to a 10Base-T Ethernet network. In addition, the Eclipse CD-ROM towers from CMS Enhancements provide all IntranetWare, NetWare 4, and NetWare 3 clients instant access to up to 14 CD-ROM drives.

Like a CD-ROM tower, a CD jukebox holds multiple CD drives. Unlike a CD-ROM tower, however, a CD jukebox also stores the CDs themselves and has a robotic arm capable of automatically inserting these CDs.

DISC Inc. offers CD-ROM jukeboxes that support up to 16 CD-ROM or CD-R drives. These jukeboxes, which hold anywhere from 238 to 1,478 CD-ROMs or CD-Rs, can exchange these CD-ROMs or CD-Rs in as little as 3.5 seconds--up to 800 exchanges per hour. Cygnet Storage Inc. also offers CD jukeboxes that support up to 16 CD-ROM or CD-R drives and hold 250 to 500 CD-ROMs or CD-Rs.

No DVD-ROM jukeboxes are on the market yet, largely due to the fact that no DVD-ROM drives with a SCSI interface exist. Within 90 days of the release of a DVD-ROM drive with a SCSI interface, which is expected to occur by the end of 1997, Cygnet Storage claims that it will ship a DVD-ROM jukebox.

FILLING UP ALL THAT SPACE

You may not immediately need the capacity offered by today's mass storage solutions, but you will eventually require this capacity. Applications and files keep growing because users continue to add more complex elements, such as graphics, audio clips, and video clips.

Fortunately, Novell is way ahead of you. The next version of IntranetWare--code-named Moab--will include Novell Storage Services (NSS), which holds files of up to 8 TB. (See "Hold Your Breath for Novell Storage Services.") NSS is designed to support all new mass storage technologies--even technologies, such as atomic force microscopes (AFMs), that sound like science fiction today. AFMs burn pits so small that they are measured in billionths of a meter, or nanometers, which may provide areal density in the hundreds of gigabits per square inch. Although AFM is still in the development stage, within 10 or 20 years, AFM just might be the technology behind the mass storage solution you choose.

You can view a list of mass storage-related web sites and companies at http://www.novell.com/nwc/nov.97/massn7/vendor.html.

Linda Boyer works for Niche Associates, which specializes in technical writing.

NetWare Connection, November 1997, pp. 6-21