The past few years' evolution of data processing technologies can rival even science fiction in its ability to amaze. PCs have both fired and been the exemplars of quantum-speed growth and change. We've gone from machines with no hard drives at all, through ones where 20M was considered cutting edge, all the way to one-gigabyte drives becoming commonplace. Memory and processor speed have taken similar leaps forward. But perhaps the most radical recent development in data processing technology is the introduction of optical data storage and its corollary multimedia capabilities into the PC equation. Furthermore, the case could be made that CD-ROM storage has its greatest impact in networked environments.
The existence of a network implies great attention to the need to distribute information in a timely fashion. Another of a network's reasons for being is the business advantage it offers. (Knowledge is not only power, it's also efficiency and effectiveness.) Unfortunately, a network link is not the best method for handing out some kinds of data. Large volumes of information that are only periodically updated or massive amounts of data regardless of the update ratio are frequently found on networks but aren't well-suited to being distributed by traditional networking methods and media. CD-ROM drives, however, can pass this stuff along with one hand tied behind their backs because of their enormous data storage capacities and their admirable data transfer abilities.
It's for these same two reasons that CD-ROMs have become the distribution media of choice for more software than you can shake a stick at. There are over 10,000 software titles that offer no other distribution medium than a CD-ROM. The following table summarizes only a small percentage of the very significant PC software available on CD-ROM.
Software Available on CD-ROM
Operating Systems
IBM OS/2
Microsoft Windows NT
Novell NetWare
UNIX (several flavors, including SCO)
Windows 95
Office Suites
Lotus SmartSuite
Microsoft Office
Novell Perfect Office
Applications
Word
WordPerfect
1-2-3
CorelDRAW!
Access
You already know the basics about CD-ROM drives from chapter 6, "The Workstation Platform." Additional benefits of using CD-ROM drives include
The characteristic that most distinguishes CD-ROMs from all other storage media is the same quality that makes them particularly valuable in a network setting: their unique combination of storage capacity, data integrity, and easy accessibility. While there are some tape systems that can rival CD-ROMs in the volume of data they're able to store, no tape can protect data as well as a CD-ROM can or retrieve it as quickly.
Let's discuss some of the characteristics of CD-ROM drives that are particularly relevant to networks. Among these are speed of access to data, speed of transfer of data from storage medium to memory, the amount of preparation time a device must put in before it is ready to begin data retrieval (also known as access time), and the amount of buffer space a device holds within itself.
NOTE: A buffer, whether in memory and known there as a cache or on a storage device and referred to simply as a buffer, is a subset of storage held aside for some special purpose. In RAM, it's used for quicker access to frequently used data or program instructions. On a storage device such as a CD-ROM drive, a buffer does a similar job, holding data whose retrieval is otherwise deterred by unevenness or irregularities in the flow of data.
Quadruple, or quad (denoted by 4X), speed not only denotes the current top rate at which most CD-ROM drives in common use can transfer data, but also testifies to the rate of development of this particular technology. It's only within the past year or so that we've gone from double-speed to quad CD-ROMs as the standard. The "single-to-double" phase of CD-ROM evolution, on the other hand, lasted about two years.
4X CD-ROM drives move data at up to 600 kilobytes per second (K/sec). They outdistance 2X drives by a factor of--you've got it--two. Those storage stalwarts of last year pushed bits at only 300 K/sec.
TIP: Applications like animation or video, which not only take in but also create huge amounts of data, are best served by 4X CD-ROM drives. The higher data transfer rates of these devices helps ensure smooth, flowing movement of the images produced.
CD-ROM Drives--Continuing To Evolve at Quantum Speeds
As the song says, "You ain't seen nothin' yet." Many manufacturers are about to or already have released six-speed (6X) CD-ROM drives, which ship data down the line at 900 K/sec. The advantages of such throughput to data-intensive networked applications like graphics and databases is self-evident. But because 6X drives are very new and correspondingly expensive, you should consider them for your environment only if the volume of data you must transfer is so large as to make throughput your only concern. On the other hand, the price of a 4X drive has been cut in half, and easily in half again, during the species' brief lifespan; 4X drives that once cost $900 now retail for about $250. This factor alone might be the best reason to choose a 4X CD-ROM drive as a network storage subsystem.Newer still are 8X CD-ROM drives. These shouldn't even be considered as a component for your network, at least for the immediate future. Their speeds of access and retrieval are fantastic, but these most recent CD-ROM devices have demonstrated a number of bugs, particularly in configuring, that rule them out of consideration for the next few months.
But while you shouldn't run out to purchase an 8X CD-ROM drive, you might, if your network must handle a large volume of archival data, consider purchasing a CD-ROM drive that can record as well as read. One such device is the Spresa 920 from Sony, which can function as a single- or double-speed internal CD-ROM reader and recorder. Other vendors such as Yamaha produce similar components. The Spresa is a SCSI-controlled component; other such devices may have proprietary controllers.
As previously mentioned, the unique combination of storage capacity, data integrity, and easy accessibility of these components makes them particularly well-matched with networks.
Access time is that period needed by any data storage device to prepare itself to retrieve the information you've asked for. This includes locating the bag of bytes, as well as moving to its site. A good 4X CD-ROM drive should find (as opposed to display to you) the item you've requested in no more than 600 milliseconds, particularly since this level of access can even be found in some 2X drives. 4X devices with the best access times can find what you're looking for in as little as 300 or 450 milliseconds.
Consider this as a means of appreciating these intervals: human reaction time--that is, the time between, let's say, your eye recording the image of a tree and your saying to yourself "What a lovely fir!"--is about one-tenth of a second. An "average" 4X CD-ROM drive's access improves upon this rate by about 300 times.
NOTE: Access times have the greatest effect on overall application performance when dealing with very large databases.
The variation in access times arises out of the fact that CD-ROM drives, dealing as they do with different types of data, have a variety of access times. This, in turn, is due to the varying rates at which CD-ROM-stored data can be read. Audio input, for example, is normally read at 150 K/sec, while graphics are ingested at 300 K/sec, and "just data" data at rates as high as 600 K/sec. Since the drive has no way of knowing till it gets to it what type of data, and in what order, it must read, CD-ROM drives must slow down upon approaching audio, speed up when getting close to data, and so on. The variation in read speeds between categories of information is responsible for the variety of access rates that CD-ROM drives demonstrate.
NOTE: Remember that getting to data is a different function and is therefore measured in a different way than transferring that data. Access time represents the getting to and has a single, flat measurement in time, such as 450 milliseconds. Transfer, on the other hand, is expressed as a ratio of so much data per such-and-such an amount of time, as in 600 K/sec.
NOTE: Another factor affecting access time on CD-ROM drives is the layout of the CD-ROM itself. Data is imprinted on it in concentric circles. Therefore, finding and reading data at the outside edge of the CD-ROM takes longer than searching out data near its center.
TIP: Any drive with an overall access time larger than 300 milliseconds shouldn't be considered as a component for your network.
Plextor, a leading manufacturer of CD-ROM drives, recommends considering transfer rate (for example, 600 K/sec) as more important than access time in selecting a drive, if these two criteria turn out to be the deciding ones.
Top-performing CD-ROM drives have a data buffer of 256K. Even lower-end models buffer their input in appreciable chunks, the most common being 64K.
The ability to send data to the CPU in more readily managed units, provided by buffering of any sort, speeds up overall throughput because it allows the CPU to take a break, lessening the likelihood of the processor's being bogged down by a large, lengthy stream of data.
Not only the presence of a buffer, but also something called the buffer-full ratio (BFR), influences a CD-ROM drive's transfer rate. The BFR is a measurement of how full a buffer must be, relative to the total size of the buffer, before the drive will actually transfer data to the CPU. Too large a BFR slows overall processing almost as much as a complete lack of buffering and for the same reasons. The CPU again bogs down under the weight of too much data sent to it too fast. A very small BFR, on the other hand, and its corollary more frequent transmissions to the processor, will tie up that engine in another way--too many individual requests that it must respond to.
TIP: Look for a BFR between 45% and 65%. For a CD-ROM drive with a 256K buffer, this works out to beginning data transfer when the buffer holds between 115K and 165K.
Recent tests by PC Magazine showed little if any difference in performance between Enhanced Integrated Device Electronics (EIDE) and Small Computer Systems Interface (SCSI) controlled drives.
When considering drives that employ these disparate controllers, keep the following sections in mind. They'll make factoring a CD-ROM drive into your network's equation much simpler.
EIDE Drives. EIDE drives, sometimes called ATAPI, are easier to install and configure than their SCSI counterparts. If yours is one of the many environments that still employs IDE controllers, incorporating an EIDE drive into your configuration is as easy as adding an adapter.
SCSI Drives. SCSI controllers can support larger, more powerful devices. They can also manage more components than IDE or EIDE interface boards. A SCSI controller allows you to daisy-chain up to seven components from itself. What's even better, these seven can communicate among themselves without having to route those conversations through a PC's CPU, which is to say that SCSI controllers are less likely to engender bottlenecks. In a network that demands ease of expandability coupled with a high degree of reliability, SCSI is the way to go.
NOTE: SCSI controllers, no matter what types of devices they manage, open up expansion slots in a PC. That's one reason they were developed, and it's still one of their most important contributions.
Another reason for considering a SCSI-based CD-ROM drive, particularly in a network setting, is that SCSI more readily supports multitasking and is the only controller that can unite Apples and PCs. Macintoshes don't have IDE capabilities but do have a SCSI port.
TIP: SCSI controllers come in 8- and 16-bit versions. The 8-bit SCSI cards are adequate for handling 2X CD-ROM drives. But the transfer rates common to 4X CD-ROM drives and the volume of data encountered in many CD-ROM-reliant applications such as graphics are such that a 16-bit board is necessary with these faster CD-ROM delivery systems.
Proprietary Controllers. Mitsumi, Panasonic, and Sony are among the many manufacturers of CD-ROM drives who offer proprietary interfaces for those drives. Such boards are usually quite inexpensive. However, they do tie you a little more tightly to the particular vendor. If ease of upgradability is a significant concern, proprietary interfaces aren't an option.
Chinon, Plextor, Sony, and other major CD-ROM drive manufacturers offer internal and external drives that are, functionally, mirror images of one another. The only difference in these components is where they sit.
External CD-ROM drives rest quietly beside your computer, occasionally and covertly blinking in red or green. However, external components do have drawbacks. For instance, external CD-ROM drives, like external modems or hard drives, are more expensive than their internal counterparts, by as much as $100 per model. On the other hand, they are light-years easier to install and configure. In addition, performance criteria such as access times and data transfer rates are identical within models between the external and internal members of that model.
NOTE: External drives offer the additional advantage of being portable--that is, easily transferred between servers.
External drives are predominantly SCSI devices. Only a few IDE external CD-ROM drives are available. Because connector cables for IDE and EIDE devices are about 18 inches long, any device they attach to must nestle side by side with its host computer. On the other hand, SCSI cables can be up to three meters long, thereby allowing some breathing room between drive and computer. Even this asset can have its problems, though. SCSI devices can sprawl out to take up too much desk or counterspace. If your workspace is limited, this "extension cord" capability of SCSI can become a drawback, particularly if you take advantage of the SCSI controller's ability to daisy-chain.
Ease of Installation. Anything more frustrating or stress-inducing than disassembling a network node, installing a new internally housed component, and reassembling and bringing back online the enhanced machine under a tight deadline is hard to imagine. Since most of us work under what might be called the "I need it yesterday" imperative, the much greater ease of installing an external CD-ROM drive is one of its most attractive characteristics, at least balancing out its cost.
CAUTION: Some external CD-ROM drives connect to their host by means of a parallel port. Since such a port sports a throughput rate worthy of a tortoise, as little as 30-40 K/sec, be sure to know the type of port any CD-ROM drive you're considering talks to.
Audio Connectability. If you intend to make any use at all of the sound capabilities of a CD-ROM drive--for instance, in creating multimedia presentations--there are a number of points you must keep in mind.
Talking to Internal CD-ROM Drives. Internal CD-ROM drives should offer Red Book-compliant analog audio connectors and should be bundled with enough cable to hook up to the (similarly Red Book-compliant) audio connectors on the sound card through which they talk.
Talking to External CD-ROM Drives. External CD-ROM drives, on the other hand, must offer analog line-out RCA connectors if you're to use CD-ROMs to help build those dynamite presentations.
A Blueprint for a Networked, Audio-Capable CD-ROM Drive. If your network needs sound, the CD-ROM drive that provides it should, in addition to the traits already presented, have the following minimum characteristics:
TIP: Microsoft's specifications for sound-related application program interfaces and drivers are recommended here largely because, as is the case with so many types of applications, software in this sub-genre was developed to adhere to the Microsoft standard. You can't go wrong by using these criteria.
NOTE: CD-ROM drives will often be used in a network setting as servers. Therefore, audio connectivity is probably the least important consideration in evaluating these subsystems for many people. But CD-ROM-driven audio is a topic of some complexity; pitfalls might await anyone trying to provide sound across a network. The information just provided should put the administrator who must provide sound on a network on firmer ground.
Loading. Some CD-ROM drives are more fastidious than others in protecting their media. Such devices use plastic caddies or cases into which a CD-ROM must be placed before it can be dropped into a drive. While caddies do minimize the potential for damage that any data storage medium is heir to, they also increase both cost and transfer speeds.
Another trait of caddy CD-ROM drives that can present problems is the nature of their loading and closing mechanisms. Automatic-loading drives begin to close and attempt to start spinning when a CD-ROM and its caddy are about halfway into the drive. This characteristic, intended to facilitate loading discs, can result instead in damaged drives when users mistakenly try to jam the caddied CD-ROM all the way into the device.
NOTE: Manual caddy drives are available and are considered virtually impervious to damage by even the impatient or inept.
In a "fast-food data" scenario, a caddyless, multi-disc drive might be your best option. Internal multi-disc CD-ROM drives most frequently offer a three-disc carousel. External multi-disc CD-ROM drives currently available can hold six or seven CD-ROMs at a time.
CD-ROM Changers. The next step up on the CD-ROM ladder is a CD-ROM changer. One such device, the DRM-1804X from Pioneer, houses three six-disc carousels. Such a storage device, while it does not provide simultaneous access to the media it houses, does greatly increase the overall capacity and decrease time needed to change those media.
To use any CD-ROM changer, you need specialized software to manage it. One such package is CD-View, from Ornetix. CD-View allows a dedicated PC housing a CD-ROM changer to emulate a NetWare server. Therefore, any Novell workstation can map and attach to this pseudo-server and access the CD-ROM drive it offers.
CD-View, unlike other similar packages, supports IDE-, EIDE-, and SCSI-based CD-ROM drives. But don't think that loading CD-View makes a machine into a real server. It doesn't; NetWare-specific configuration tasks like tailoring security must be done with SYSCON, from a true NetWare server.
Always-Available CD-ROMs. The mirror-image to a CD-ROM changer is what's known as an always available or real-time CD-ROM drive. Such devices can keep a number of discs loaded simultaneously. As their names imply, these drives are sophisticated mechanisms.
To this point, we've covered a lot of ground. Table 24.1 traces our steps, presenting the most important characteristics to be considered in selecting a CD-ROM drive that will become part of a network. (The table even contains a few less central CD-ROM traits that haven't yet been presented. Those have been indicated with an asterisk.)
| Characteristic | Look for These Qualities |
| Access Time | No more than 450 milliseconds overall. |
| Caddy? | Only if protection of discs is of prime importance. Even then, make sure the drive is a manual loader. |
| Data Transfer | 600 K/sec (the rate demonstrated by a good 4X drive). |
| *Drive Door | Two doors--one door flush with the chassis, and the other door within the drive bay. This combination offers the maximum environmental protection to drive and discs. |
| *Driver Size | No more than 80K of conventional memory. |
| *Eject Mechanism | Motor-driven and easily accessible. |
| External or Internal? | The answer to this question is dependent upon several factors: Accessibility/availability
of drive bays Nature of interface V olume of data to be stored |
| In turn, the choice between an external or an internal CD-ROM drive affects the choice between a dedicated or a shared network CD-ROM server. | |
| Loading Mechanism | Manual load if high volume and simultaneous access aren't important. CD-ROM changer if neither simultaneous access to media or a high volume of media in use at any given time is a factor in your environment. |
In a network, CD-ROM drives act very much as they do in stand-alone PCs, with a single very important exception. Such a drive's ability to simultaneously maximize storage and retrieval rates is even more important in a network than on an autonomous machine. As mentioned earlier, data-intensive applications like graphics will benefit from CD-ROMs in any setting. Factoring in the overhead that sharing such applications and their data across a network places on things like throughput makes choosing the right network CD-ROM drive even more critical.
CD-ROM drives intended specifically for the heavier loads and more frequent access of a busy network can be of two types: jukeboxes or towers.
NOTE: Jukeboxes and towers are actually the two major varieties of CD-ROM changers.
Each of these categories incorporates all the characteristics of CD-ROM drives discussed to this point. Each also goes beyond those basic CD-ROM traits by offering a scheme for rapid access to multiple media.
Like their audio alter-egos, jukeboxes operate by selecting a specific disc from an ordered group or stack. Jukeboxes are the simpler multi-CD-ROM mechanisms; some of the physically smaller of them can be incorporated into a PC. Assuming your server has a free bay of the appropriate size, installing a jukebox is feasible.
NOTE: The question of dedicated versus shared just peeked around the corner again. Even a jukebox, which is a pretty sophisticated way of delivering CD-ROM-based data to your users, cannot act as a dedicated server unless one of those old but still functioning PCs you noticed back in the storeroom can accept the jukebox.
CD-ROM towers house a number of individual CD-ROM drives. They allow your users access to several or as many as a dozen discs at once. The total number of discs available will of course be the product of the number of drives a tower contains and the number of discs each of those drives can handle.
TIP: Oddly enough, some jukeboxes can flip a larger total number of CD-ROMs than some towers. However, no jukebox can do what every CD-ROM tower can: offer simultaneous access to all loaded discs.
Most of the highest-performing CD-ROM towers are SCSI devices, many of which can be hooked to other, similar towers, or can house other SCSI devices such as tape drives in the same case that holds the CD-ROM drives. In addition, the component drives of some towers take a "multi-connectivity" approach. That is, these drives include an integral Industry Standard Architecture (ISA) controller, the drive's 50-pin SCSI connector, and its power connector. This clustering of connections makes it easier to change an individual drive within a tower.
Management of CD-ROM towers can usually be accomplished through the NOS. The NOS deals with the tower as it does any file server. However, because of their muscle and complexity, CD-ROM towers benefit from third-party management software. The best of the big guys come with such software bundled.
Smart Towers. Some large jukeboxes and many of the latest towers have their own CPU and therefore can connect directly to a network. Smaller jukeboxes or older towers must be physically attached to a server, which brings up the quintessential networking question, "What if the server goes down?" If you're running most jukeboxes, your CD-ROM users, like all other users, have only one option--to take a break and get a cup of their choice beverage. If, on the other hand, you've implemented one of the new, smart CD-ROM towers, users accessing data or applications dished out by it just keep on trucking.
Even if your network is relatively small, you expect its extent, complexity, and heter-ogeneity to continue to grow. So don't consider a shared drive. Nor should you give a second glance to a dedicated internal CD-ROM server because it lacks the ability for simultaneous access to multiple discs, as do even the biggest and smartest jukeboxes.
Go straight to the CD-ROM towers of your favorite Value Added Reseller (VAR), a retailer. There, select a tower with the following characteristics:
This tower could keep 27 CD-ROMs loaded and available to your users simultaneously. Assuming that each of those discs is actually holding about 50M, we're talking about 1.35G of data being online at any given moment.
Much of the chapter to this point may seem to have had a slant toward dedicated CD-ROM servers. We've noted paradoxes like that of the much easier to deal with but also more expensive external CD-ROM drive, seemingly suggesting that internal-but- autonomous is the way to go. We've included volume of usage in discussions on everything from drive loading mechanisms to accessing multiple discs, possibly implying that dedicated servers, by virtue of having nothing else to deal with, are better suited to managing the problems that high volume can engender.
Dedicated devices aren't always feasible, though. If nothing else, the expense and effort involved in implementing a dedicated CD-ROM server on your network may mandate a CD-ROM drive that must contend with other subsystems for a server's resources. Therefore, to look more closely at just what's needed to make a shared network CD-ROM drive hum is wise.
There are a number of ways to share CD-ROM drives across a network. Choosing the right one depends on several things:
CD-ROM versus NOS. Probably the most important factor in determining the mechanism by which you establish CD-ROM drive sharing is the NOS that ultimately controls that drive. Several of the most widely used NOSs, including LANtastic, NetWare, Windows NT, and Windows for Workgroups, provide software to accomplish CD-ROM sharing. Be aware, however, that this software carries some constraints. For example, the earlier versions of NetWare NLMs that permit sharing CD-ROMs don't support SCSI CD-ROM drives. So be sure to read the small print in your NOS's documentation in ferreting out whether your NOS can support the CD-ROM drive you're considering.
TIP: Under version 4.1, NetWare's CDROM.NLM supports these SCSI controllers.
| Manufacturer | Model |
| ADIC | DCB-ISA, DCB-EISA |
| Always Technology | Al-6000 |
| DPT | PM2012B, PM2011B/95 |
| DTC | DTC3280, DTC3290, DTC3292 |
| Hewlett-Packard | LM-SCSI |
Detailed information on mounting a CD-ROM drive as a NetWare volume can be found on the Web at the following address:
http://www.zdnet.com/~coop/netware/9501/ntware1.home
A CD-ROM Drive on a Peer-To-Peer Network. Another, related factor is whether your network is peer-to-peer or client/server. In peer-to-peer networks, it is possible to share CD-ROM drives. However, this network algorithm adds a wrinkle or two to drive-sharing.
First, a shared CD-ROM drive on a peer-to-peer network must exist as a component of a dedicated workstation. So if you haven't gone back to the warehouse to look for that old 486, you'll have to do so now. You'll need it to house the CD-ROM drive that's to be shared across your peer-to-peer network. Once this dedicated station has been incorporated into the network, your users need only to map or attach to it to use the drive.
Second, your users have to load the Microsoft CD-ROM Extensions TSR utility, MSCDEX.EXE, at their station. It can't live on the dedicated station where the CD-ROM drive resides. In addition, all users must employ version 2.22 or higher of MSCDEX.EXE.
Hierarchical Sharing--the Novell Connection. NetWare's handling of shared CD-ROM drives is typical of how LAN operating systems manage these devices. When you combine this functional characteristic with NetWare's role as market leader among NOSs, we should take a closer look at administering shared CD-ROM drives under NetWare.
CAUTION: NetWare supports shared CD-ROM drives, with two important constraints. First, its default implementation doesn't support IDE- or EIDE-controlled CD-ROM drives. If you intend to use one of these, you'll need add-ons in the form of patches (see appendix A, "NetWare Patches") or of third-party software. Second, with versions of NetWare prior to 3.12, you cannot share CD-ROM drives of any kind.
If the CD-ROM drive you're going to be sharing isn't already present in or attached to an existing NetWare server, you of course must install it according to manufacturer's instructions. Then you must load the drivers for the drive itself and for any new interface board it may have brought with it. Only when these steps are complete can you load drivers that share access across your network to the new CD-ROM drive. This second category of drivers may be provided by Novell as NLMs or may be made up of third-party packages.
NetWare includes a file called ASPICD.DSK on its SYSTEM_2 disc. This file is its driver for shared CD-ROMs. However, ASPICD.DSK is not loaded during NetWare installation. So you'll have to manually copy ASPICD.DSK to an appropriate path on your server.
Another constraint that NetWare imposes on the management of shared CD-ROM drives is that it not only caches the volumes resident on these drives but indexes those volumes the first time they're mounted to provide faster access during subsequent mounts and dismounts. Given this scheme, you'd be well-advised to allocate additional server memory to handle CD-ROM drive volumes.
As is the case with all its security arrangements, NetWare controls access to shared CD-ROM drives by means of groups. The default is to give access to such drives to the EVERYONE group. Trouble is, EVERYONE is just that--this group most frequently includes all user accounts. If you need to narrow this generous focus, you'll have to do so from the command line prompt at the network console while the CD-ROM volume is being mounted.
This need to tailor access to a shared Novell CD-ROM drive emphasizes the only really weak point in NetWare's management of such drives. In any environment in which CD-ROM volumes must be mounted and unmounted regularly, the opportunity for unauthorized use of the server console increases. The corollary possibility of damage to network services by an inexperienced, inept, or simply curious user grows along with that.
To preclude such damage, there are a few things you can do. First, if their size doesn't preclude it, you could simply allow the CD-ROM volumes to remain mounted at all times. Second, you could remove the keyboard and even the monitor from the server that contains the shared drive and manage that server remotely by means of RCONSOLE. Third, you could limit access to the shared drive to users knowledgeable enough to mount or dismount it correctly.
If You Want To Be Really Sure. There are other, higher-tech and lower-likelihood-of-failure means of controlling access to network servers that include shared CD-ROM drives. One is a hardware device called Discport from Microtest. Discport is analogous to a modem. In fact, it looks a lot like an external modem, being about the same size and shape. Discport has a network connector at one end of its cable and a SCSI connector at the other end. The network connector can be either Ethernet or token ring. At its SCSI end, Discport can talk to as many as seven CD-ROM drives.
Management of the drives Discport connects is done through its bundled, Windows-based application, Discview. Discview allows authorized users to mount and dismount CD-ROM volumes by clicking an appropriate icon; no chance for console command syntax errors here. Discview also can be used to access specific CD-ROMs that are already mounted.
Implementing the Discport/Discview combo doesn't preclude less flashy paths to NetWare CD-ROM drives. For instance, users can reach mounted CD-ROM volumes with the familiar MAP command. They'll never know that Discport and Discview are sitting between them and their NOS because MAP executes exactly as if it were being processed by NetWare itself.
Older NOSs. For NetWare releases predating 3.12, and for older versions of other NOSs, there is still a way to share CD-ROM drives across the network. In such cases, what's needed is the addition of third-party software to the configuration. Such packages supply drivers and management tools to the NOS that allow it to network CD-ROMs. Two such products are systems from Meridian's CD Net and Online Products Corpora-tion's OPTI-NET. Comparing these two accurately is difficult because each requires a different mix of hardware and software. The Meridian system, for example, handles inquiries from multiple workstations quite well but is not as quick as other packages in responding to requests from individual workstations.
Since the discussion of shared CD-ROM drives has, to this point, gone on largely in a Novell context, let's continue along that path, and take a look at one of these third-party applications in terms of how it can be used to augment an older Novell network. OPTI-NET is a LAN management program that supports networks fully implementing NetBIOS or IPX/SPX. OPTI-NET extends networking capabilities to CD-ROM drives, allowing users to share data housed there. The application connects CD-ROM drives to NetWare and allows those drives to be managed from NetWare.
NOTE: OPTI-NET is a software-only solution; therefore, existing network hardware need not be enhanced. OPTI-NET also runs under PS/1 and PS/2.
The OPTI-NET Value Added Process (VAP) version allows CD-ROM drives to be connected directly to a dedicated file server or to an external bridge. The VAP version of the package requires NetWare 286 Release 2.1 or later.
Software drivers for SCSI controllers are integrated into OPTI-NET VAP. Up to 28 drives per CD-ROM server are possible. OPTI-NET supports an unlimited number of CD-ROM servers per network. In addition, at each server that it supports, OPTI-NET can grant CD-ROM access to up to 100 simultaneous users, depending on the network type and the maximum number of sessions supported. Finally, OPTI-NET supports up to 64 CD-ROM drives per server and offers remote or centralized management tools because it does not require a dedicated server.
TIP: Even the simultaneous use from the same machine of a local CD-ROM and a CD-ROM shared across the network by means of OPTI-NET is possible. You simply use two different device names: one for the local driver and another for the OPTI-NET NETUSR device driver.
Don't look now, but there's a networked CD-ROM drive disaster of some sort out there, and it's looking for you. You can elude it if you do the following.
Be meticulous in configuring access to your CD-ROM server, particularly if that "server" is actually a shared drive. Do nothing that might open a door for the inexperienced or the curious to experiment or interfere with the drive's operating parameters.
Keep duplicates of frequently used CD-ROMs immediately at hand, and copies of less-frequently accessed media not much farther away. Keep another set of copies of each of these in off-site storage that is as disaster-proof as possible: protected from fire, impact with heavy objects, and so on.
If your network is large enough or busy enough to justify a CD-ROM tower, it's also large and busy enough to need some of the drives in that tower to function as mirrored discs. Make use of this built-in opportunity for data redundancy.
Most failures of storage subsystems are electro-mechanical in origin. A cable or interface card, rather than data on the device it supports, will probably be the first to die. Protect these less glamorous network components. Adhere to the following rules:
This chapter began with a brief reflection on the quantum speed with which data processing technologies evolve. We conclude it with a look at one way in which that progression continues.
One of the newest sights on the connectivity horizon is Asynchronous Transfer Mode (ATM) networking technology. ATM was developed specifically to support the transmission of multiple, differing types of information, including audio, image, text, video, and voice, by a single switching interface. ATM is, for all intents and purposes, without any real transmission speed or throughput limitations. It can support a number of users from the relatively few that frequent a LAN to the many to be found on a WAN.
Perhaps most relevant to networked CD-ROM drives are two other characteristics of ATM. The new technology is isochronous. That is, it is transparent to the timing dependencies of data such as audio. Further, ATM interfaces are multimedia-ready and can increase or decrease bandwidth on demand.
Two examples of what ATM can offer are two NICs from Sun Microsystems. The ATM-155/MFiber adapter accomplishes 155 Mbps transmission over multimode FDDI channels. The ATM-155/UTPS card operates at 155 Mbps over Category five UTP cable. Both of these boards send not only text and graphics but also audio and video signals at the 155 Mbps rate. Both demonstrate low latency and high reliability.
Just approaching the networking horizon are the second generation of ATM cards. A number of vendors, among them Toshiba America Electronics Components, PMC-Sierra, and Siemens Components, brought to the 1995 Networld-Interop Conference their renderings of this second generation. While these latest ATM interfaces still operate at 155 Mbps, they offer improved formatting of data in preparation for transmission, as well as integration into a network at the physical layer. This latter is accomplished either through a multi-chip set with a PCI interface or by a single chip that integrates a PCI interface with a DMA controller. The single-chip card is clever enough to be able to access data without the help of other, off-chip memory on the card.
What's so exciting about ATM in the context of this chapter? ATM's inherent ability to simultaneously transmit several types of data. Most of our discussion of networked CD-ROM drives has involved making a number of choices: between internal and external, dedicated or shared, and mounted/dismounted or always-available servers. ATM, with its beefy bandwidth and throughput, may make such decision-making a thing of the past. Trading in even our idealized, nine-drive "super-tower" for a single ATM server would improve rather than reduce user access to CD-ROM-based data.
CD-ROM drives, because of their huge data storage capacities and their unsurpassed data transfer speeds, are particularly suited to networks. In addition, the collection of software titles that offer no other distribution medium than a CD-ROM could very well include some of your network's most important applications; such titles number more than 10,000. Finally, the ability of such sophisticated CD-ROM devices such as jukeboxes and towers to offer access, even simultaneous access, to multiple storage media and to multimedia data assures CD-ROM technology an ongoing role in distributed data processing environments.
One recent development that testifies to this role is the announcement in November 1995 by AT&T of a plan for a new multimedia communications server that it expects to be the cornerstone of its strategy for integrating voice and data transmissions over LANs. Called the Multimedia Communications Exchange Server, this combination of hardware and software will support real-time voice, video, and data applications. According to the October 30, 1995 issue of Communications Week, the Exchange Server will run under UNIX on an Intel 120 MHz Pentium processor, will interact with Hewlett-Packard and Sun Micro-systems workstations, will support up to 100 concurrent users, and will encompass client/server applications, protocol conversion, and even some network management functions. The Multimedia Communications Exchange Server will be tested in 1996, but general availability is not expected until 1997. (Other vendors, such as IBM and Microsoft, are considering a similar approach to networking multimedia.)
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