How to share CD-ROM drives & applications, even multimedia, under NetWare
Lite, Workgroups for Windows, LANtastic

The keys are CD-ROM caching and prefetching

By Chris Magyar
Software engineer for OPTI-NET family
of CD-ROM networking products

Online Computer Systems Inc.
20251 Century Blvd.
Germantown, Md. 20874-1196

Sharing CD-ROM-based data and applications -- especially multimedia
applications -- will bring any peer-to-peer network to its knees.

Guaranteed -- unless CD-ROM caching and prefetching are added to the
network as a way of providing faster access to more data and returning
productivity to the community of users.

Yet not just any caching and prefetching will suffice.

Consider a medical practice with 20 workstations operating under NetWare
Lite, Workgroups for Windows, LANtastic, 10Net or PowerLAN. Client billing
records are archived at the server, which also supports a shared printer
and two CD-ROM drives.

Dr. Jones uses the first CD-ROM drive to research the AIDS Compact Library.
At the same time, for a patient, a med-tech prints a guide to resources
and support groups compiled from The New England Journal of Medicine
1986-1993, which is running on the second CD-ROM drive. Concurrently, the
office manager searches the archives for outstanding invoices. And Dr.
Smith logs on to also work with the AIDS Compact Library.

Without CD-ROM caching and prefetching, everyone in the office may as well
put in a round of golf, because the system will be decidedly less than
responsive.

Technology is at fault

Peer-to-peer networks using MS/PC-DOS and Windows are subject to the
performance constraints of those systems. Specifically, any magnetic drive
input/output (I/O) operation -- for example, the office manager searching
the archives stored on the server's hard disk -- halts the operating
system until the operation completes.

Further, when a user accesses the server's hard drive, the server must
interleave that access with all other server activity -- the research by
Dr. Jones and printing by the med-tech. As user activity increases, server
performance degrades, because the server is forced to allocate a fixed
amount of memory and other system resources among an increasing number of
tasks.

Simply, network users get to know the Windows hourglass well.

The problem worsens when sharing a CD-ROM drive. A CD-ROM drive provides
access times of 300 milliseconds, almost 20 times slower than the common
hard disk with 16ms access times.

That means any access to a shared CD-ROM drive perceptibly staggers the
network more than any access to a shared hard drive. It affects both the
user accessing the CD-ROM drive, and every other user attempting to access
shared resources on the server.

The problem becomes an order of magnitude more acute as users adopt
increasingly popular multimedia applications.

Consider two users of a shared CD-ROM drive, each using that drive to play
a different video clip. The drive finds the first clip on the CD and
begins to play it back for the first user. The second user accesses the
second clip. That forces the CD-ROM drive to move the read head across the
CD to find the second clip and start to play it back. Then the drive moves
back across the CD to play the next segment of the first clip. And so on.

The act of moving that head back and forth across the CD is measured in
real time. It can take 6 seconds in head-seek time alone for an MPC-spec
CD-ROM drive with an access speed of 300ms to transfer the 20 to 30K of
data needed to just begin a video play back. Add more users and this
becomes worse, in a hurry.

Why share CD ROM drives?

Dr. Jones discovered the AIDS Compact Library, bought a copy, and the
network administrator added a CD-ROM drive, adapter and software driver to
the doctor's workstation.

Dr. Smith has to push Dr. Jones off that PC to use that same disc. Or the
office has to buy a second drive, adapter and software driver, and a
second copy of the disc.

And the med-tech can't get access to the CD-ROM drive added to either PC
until one of the doctors is finished. Yet patients are waiting, so the
med-tech wants a CD-ROM drive for a third PC, too.

This may be the easiest way to provide access to the gargantuan volumes of
data available on CD-ROM -- and the compelling new multimedia-based
applications available only on CD-ROM.

But it's very expensive -- especially if each of the other 17 coworkers in
the office decides that they too want a drive and their own copy of the
same CD-ROM software.

The alternative is enhancing the peer-to-peer network as a far more
cost-effective way to provide shared access to CD-ROM-based information
and applications. A server configured with two or three CD-ROM drives --
instead of 20 separate drives, one at each workstation -- might meet the
needs of every user in the office. Moreover, that access is network wide,
available to every user, not just Dr. Jones, or only Dr. Smith, or only
the med-tech.

The problem is ensuring faster access to more applications and volumes of
data stored on the inherently dawdling CD-ROM drives.

Technology to the rescue

Two technologies provide a solution to the problem. When added to shared
CD-ROM drives installed on the servers of peer-to-peer networks, CD-ROM
data caching and CD-ROM data prefetching boost network performance and
user productivity.

For reference, both technologies are integrated into one product, OPTI-NET
Lite, a software utility from Online Computer Systems Inc. and the newest
member of the OPTI-NET family of CD-ROM networking software.

For larger networks, OPTI-NET DOS, VAP and NLM enable users to share,
manage and add caching and prefetching to server-based CD-ROM drives and
applications under MS/PC-DOS, NetWare 286, and NetWare 3 and 4,
respectively; OPTI-NET NLM is certified by Novell.

CD-ROM data caching enables network users to store recently and
frequently-used applications and data in high-speed extended memory (XMS),
for almost instant retrieval. This significantly reduces the number of
reads that are required from a CD-ROM drive -much like other disk-caching
programs use random access, extended or expanded memory to speed access to
information stored on a hard disk.

Simply, the cache temporarily copies into RAM, XMS or EMS volumes of data
from the CD ROM disc, data that the read head in the CD-ROM drive would
otherwise have to find and access over and over again.

CD-ROM data prefetching in OPTI-NET Lite uses an Online-developed
proprietary algorithm and a user-defined system buffer to predict and
retrieve the data that multiple users might request, storing that data in
the CD-ROM data cache.

Prefetching is ideal when multiple users are contending for access to a
single CD-ROM drive. Instead of thrashing about to respond to a random
stream of small requests from many users, the drive sees and responds to
an orderly stream of large requests.

Prefetching vs. read ahead

A weaker alternative to CD-ROM data caching and CD-ROM prefetching is to
combine a standard cache with a traditional single-user read-ahead
algorithm.

First, cache utilities have traditionally not worked with CD-ROM drives.
They work only with hard drives.

However, this is changing. An increasing number of products do support
CD-ROM caching in addition to hard-disk caching.

Unfortunately, these newer caching utilities come with a read-ahead
algorithm that is not the equal of data prefetching.

Why? Users are going to run data-oriented applications like Computer Select
or Books in Print, which compile volumes of data that the user queries,
much like a database. This is a repetitive operation for which cache is
well suited.

But newer CD-ROM applications integrate images, audio, full-motion video
and motion video with sound. These multimedia applications don't function
well with cache.

When a single user reads large sequential blocks of data off the CD -- a
large image file, for example -- the image will be slightly jerky. If
another user logs on, performance goes from slightly jerky to a slide
show. It may take hours for four users to play video clips, for example,
even though each clip is just minutes long.

Simply, a multi-user, multimedia environment defeats a read-ahead
algorithm, because that algorithm is designed to support only one user,
not many. With one user, the read-ahead algorithm sees an orderly string
of requests, from which it can predict and retrieve what data might next
be needed. However, with more than one user, requests become interleaved,
the algorithm sees what appears to be a random stream of requests, and it
cannot predict or retrieve what the many users might need next.
Performance falls through the floor.

In contrast, CD-ROM data prefetching is explicitly tuned to derive a
context from a seemingly random stream of data requests from multiple
users. For example, with two users, the read head of the CD-ROM drive
moves to find a block of data on the disc that the first user needs to
begin to view a large image file. Then the head moves to read the block of
data that begins a video sequence for the second user. When the head comes
back to read the second block of data for the first user, then moves again
to access the second block of data for the second user, the prefetch
algorithm "learns" to read a larger block of data for each user and to
transfer that larger block of data into the cache buffer.
The net result is that the two video clips can be played back by each user
at near the speed that one user might view a clip on a stand-alone
system.

Performance gains

The performance gains are dramatic.

The following charts detail how much faster a benchmark test using OPTI-NET
Lite ran compared to the same test without OPTI-NET Lite loaded. "CNN
Newsroom Global View" was used to benchmark performance for a multimedia
application and "Computer Select" was used to benchmark a text-based
application.

Configured on an Ethernet LAN, Workstation 1 is a 10MHz 286, workstation 2
is a 25MHz 386, workstation 3 is a 25MHz 486SX, workstation 4 is a
dedicated 33MHz 486 server, and workstation 5 is a 25MHz 486SX.

Test results are cumulative, average performance increases.

Note that all times in the tables are shown in the form of
      Hours:Minutes:Seconds (HH:MM:SS)


                          CNN Newsroom            Computer Select
                        ----------------          ---------------

LANtastic.............      2MB cache,             4MB cache,
                           64K pretetch           8K prefetch
   3 workstations.....          246%                   268%

NetWare Lite..........      4MB cache,             4MB cache,
                           64K prefetch           64K prefetch
   3 workstations.....          270%                   642%

Windows for Workgroups     1MB cache,             4MB cache,
                           64K prefetch           0K prefetch
   3 workstations.....          265%                   194%


                                 LANTASTIC

                    CNN Newsroom               Computer Select
                 ----------------------     ---------------------
                 Without     2MB cache      Without    4MB cache
                  Cache     64K prefetch     Cache     8 prefetch
                 --------   ------------    --------   ----------
Workstation 1    01:31:21     00:36:40      00:59:44    00:26:51
Workstation 2    01:27:29     00:34:29      00:53:58    00:15:56
Workstation 3    01:18:50     00:33:27      00:55:48    00:20:24


                                 NetWare Lite

                    CNN Newsroom               Computer Select
                 ----------------------     ---------------------
                 Without     4MB cache      Without    4MB cache
                  Cache     64K prefetch     Cache      64K pref
                 --------   ------------    --------   ----------
Workstation 2    01:50:29     00:40:37      02:13:41    00:19:28
Workstation 3    01:48:58     00:42:41      02:13:36    00:23:42
Workstation 5    01:57:41     00:41:28      02:12:08    00:19:04


                            Windows for Workgroups

                    CNN Newsroom               Computer Select
                 ----------------------     ---------------------
                 Without     1MB cache      Without    4MB cache
                  Cache     64K prefetch     Cache     0 prefetch
                 --------   ------------    --------   ----------
Workstation 3    00:25:37     00:19:51      00:36:53    00:20:26
Workstation 5    00:33:00     00:24:43      00:35:08    00:19:13


Summary

Caching is ideal for data-intensive applications. It works well on hard
disks. It works even better on slow CD-ROM drives.

Multimedia applications on a network don't work well with caching and
defeat single-user read-ahead algorithms. What is needed, instead, is a
multi-user CD-ROM data prefetch that integrates with the cache buffer.

The performance gain from caching and prefetching can be as much as an
order of magnitude. This makes it cost-effective and productive to share
CD-ROM drives and applications under NetWare Lite, Workgroups for Windows,
LANtastic, 10Net, PowerLAN and other peer-to-peer networks. 

Online Computer Systems Inc
20251 Century Blvd
Germantown, MD 20874-1196
800-922-9204,  301-428-3700,  fax 301-428-2903

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