ftp.cdrom.com/pub/cdrom//cdrom.tar/cdrom/textinfo/cdromnfs.txt

Text File | 1993-04-26 | 7KB | 132 lines

This is for the INN workshop on CD-ROM networking sorry for the delay
things have been heckit:

        Networking CD-ROM's with NFS: A breif review

What is NFS?

Every computing platform has its own way of sharing disk storage across
systems.  VMS has VAXclusters, and Digital's DFS (Distributed File System).
In the MS-DOS world, there are lots of contenders: Novell Netware, Banyan
Vines, and Microsoft LAN Manager (which Digital calls Pathworks for DOS),
to name a few.  For Macintosh computers, Appleshare was the first.  In the
Unix world, the most venerable and most popular is NFS, the Network File
System.  NFS was developed by Sun Microsystems during the late-1980s as a
way to link lots of inexpensive desktop workstations with Ethernet
interfaces and TCP/IP software to larger compute servers and disk farms.
NFS is one piece of Sun's answer to VAXclusters.

The general term for this  software is "distributed file system."   In the
distributed file system game, "server" always means the computer with the
disk on it.  "Client" is used to describe the systems that use the server's
resources.  On most minicomputers, a system can be both a server and a
client.  In Macintosh and MS-DOS systems,  the microcomputer generally is a
client, with many clients sharing one or two servers.

As distributed computing systems have grown, each of these distributed file
systems has grown out of its original environment.  So, we have Pathworks
on VMS (and Ultrix), which lets a VAX provide disk service to MS-DOS
systems running LAN Manager.  There are also Netware  servers for VMS and
Unix, Netware clients for Macintosh, Appleshare servers for VMS and Unix,
Appleshare clients for MS-DOS, and so on.

Why would you use NFS?

NFS has two major advantages over all of the other client/server
distributed file systems: first, it's been implemented on every major
computing platform.  Microcomputer, minicomputer, and mainframe: all
support NFS client, and many support NFS server.  Second, it's cheap.   Not
only is the client software inexpensive, but it's also cheap to install,
cheap to maintain, and cheap to manage.  NFS was designed to be simple to
implement and simple to operate, and it lives up to that very well.  Once
you've got a TCP/IP network installed, adding NFS to most servers takes
only a few minutes.

NFS also has some disadvantages.  NFS normally runs on top of Sun's RPC
(Remote Procedure Call) software, and RPC normally runs over the UDP (User
Datagram Protocol) protocol in a TCP/IP network.  While most users don't
care about such things, there is an important implication: most TCP/IP
networks don't checksum UDP packets. That means that any data which is
corrupted in passing over a network won't be discovered as "bad" by NFS.
If your application calls for high levels of data reliability, you'll
probably want to think twice before choosing NFS. Also now there are two
forms of RPC ONC and DCE which confused things further.

NFS also doesn't support sophisticated file organizations and operations,
such as indexed files or record locking.  In the NFS world, these are left
to higher-level application packages.  Security in NFS is limited to
Unix-style user- and group-id mapping.

Nevertheless, NFS makes a lot of sense for many environments.  It provides
broad access to file-based data across all significant computing platforms.
It's designed for distributed operation, which makes it easy to build very
large networks.  And it uses TCP/IP, which is better supported than
transports such as Novell's IPX or Digital's DECnet or Apples AppleTalk.

How do you do it.

If you mount an ISO format CD-ROM on you sun using
   # mount -t hsfs -o ro /dev/sr0 /cdrom
 and export it to the network using
   # exportfs /cdrom
It is then made available for mounting using NFS to other devices.

The PC can mount the CD-ROM using any NFS Client including Sun's PC-NFS.
(This is the product we use) Most PC search software requires the presence
of MSCDEX to work with the CD-ROM. Daniel Churchman of Digital Solutions
Pty Ltd, of Queensland Australia wrote a simplistic MSCDEX faker called
MXSUB in May 1990 which they release under GNU Public License in January '92.
This work well with early versions of the search software.Colin Ian King
<[e-mail]> wrote a small quantitiy of C code which fakes the MSCDEX
extensions required by many PC packages. He also produced a list of which
search software used which MSCDEX functions. This code is released under
GNU Public license and is available from ftp.york.ac.uk in /pub/cd-rom,
via anonymous FTP. This faker can work with an Microsoft Compatible Network
which can see CD-ROMs.

It is also necessary sometimes to set the volume label of the NFS mounted
drive. "Malcolm E. Sherrington" <[e-mail]> in an article in the
proceeding of the UKUUG confernce of January '93 talks about the problems
in doing this. He wrote a program call NFSLABEL to label PC-NFS mounted
Network Drives. However, this code was slow to be release and Robert
Turner <[e-mail]> wrote similar code called LABELNFS
which is available in source form. All this code is available from
ftp.york.ac.uk in /pub/pc-nfs. This code has been sucessfully used with
BRS/Search SilverPlatter and WilsonDisk search software.

The only CD-ROM search software which has been made available to me for
testing purpose, on the Macintosh is SilverPlatters SPIRS. We have a
GatorCS/Rack running GatorShare, an Apple Filing Protocol to NFS convert.
(For more info mail [e-mail]) This allows the Macs to see NFS
file store as Appleshare Volumes. To mount CD-ROM to the Mac you must do
the following:
   1) mount the CD-ROM on a Mac using a local CD-ROM. This
   will give you the Volume Name of the CD-ROM as seen to the Mac.
   2) mount the CD-ROM on the NFS server.
   3) Using GatorKeeper, the management software for GatorShare create a
   new  AppleShare Volume called the same name as the volume when the
   CD-ROM was mounted locally.
     This volume should mount the CD-ROM exported from the NFS server but the
   DESKTOP file should be create on some other section of NFS disk as it
   cannot be created on the CD-ROM. GatorKeeper will confirm the volume
   creation and then uses can mount the Volumes using the Chooser as usual.
The user community can now mount the CD-ROM over the network to their Mac
just like any other network volume and the SPIRS search software can us it.
It is possible to Automate this mount and search software to make it
transparent to the user and so limit usuage.

   It should be noted that it is important to license approriately copies
of the CD-ROMs before exporting them generally over the network. You might
also want to restrict access to appropriate netgroups. Also license
locking the search software satisfies certain companies, but not all.

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I hope the above is of use to you. I have been working on this problem
for 18 months on and off and finally I have got round to documenting it as
above. All the code mentions is Public Domain. If you wish to mirror it
please feel free as we only have limited Internet access. New updates
appear about every 2 or 3 months.