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Netdisk.zip written by Jim Christensen, Oct 1987.
What is NetDisk
NetDisk is a simple disk server for PC DOS. It allows multiple PCs connected
by a local area network (LAN) to access the disk of another PC on the LAN. We
call the PC whose disk is being accessed the "server", and the PCs who are
accessing the disk "clients".
One way of using NetDisk is illustrated by the following diagram.
+------- LAN -------+---------------+---------------+
| | | |
| | | |
|-----------| |-----------| |-----------| |-----------|
| Server PC | | Client PC | | Client PC | | Client PC |
|-----------| |-----------| |-----------| |-----------|
This PC's disk All of the client PCs can read the server's
is accessible by disk just as though it were a local, private
all client PCs. disk. A client PC may write on the server's
disk if it's the only active client.
Functional Characteristics
Requires a dedicated PC for the disk server. Any one drive on this machine
may be used for the network disk.
Allows multiple PCs to read the network disk concurrently. The network disk
looks like a new drive letter to these PCs, and each can have its own current
directory. Optionally, you can specify which PCs are allowed to access the
network disk.
Allows any PC to write on the network disk, as long as it's the only active
user of the network disk. Optionally, the network disk may be write-protected
against some or all users.
Allows multiple disk servers on the same network, and access to multiple
network disks within one PC.
Shares the network with other programs (e.g. MYTE).
Is not as fast as a local disk.
Comparison with the PC Network Program
IBM announced a program along with the PC Network that also provides a disk
server function. So why did I write NetDisk? I needed more disk space, but I
wasn't willing to give-up a lot of memory to get it. NetDisk uses about 2K of
my PC's memory. The PC Network program uses more like 130K. I grant that you
get more function for that 130K, but all I needed was the disk server
function.
Warning! I've tested Netdisk and my department
uses it in the manner shown in the above diagram. I have some confidence that
it works as designed. Be aware however that NetDisk server program uses a low
level interface to the real disk (see Implementation section). If NetDisk has
bugs in it, the server's file system could be damaged. If you plan to run the
NetDisk server on a disk with important data, I recommend that you replicate
that data on another disk or diskette.
Prerequisites for NetDisk
Before you can use NetDisk, you'll need the following:
Two or more PCs connected by a LAN. I've tested NetDisk only on the IBM
Token Ring network, but I think NetDisk should work equally well on the IBM PC
Network as the interface to PC DOS programs is the same for both of these
network adapters.
The NETBIOS programs that provide the API (i.e. the INT 0x5C interface) to
the LAN.
Running NetDisk
Once you've decided to use NetDisk, do the following steps:
NETDISK.PAC -- The table of contents for the NetDisk package.
NETDISK.TXT -- This document.
NETDISK.SYS -- The block device driver that runs in each client PC.
NETDISK.EXE -- The server program that runs in the server PC.
Client Configuration
Download NETDISK.SYS to each PC that will run as a client.
Also add a line to the CONFIG.SYS file of each client PC to install
NETDISK.SYS as a device driver at boot time. If you put NETDISK.SYS in the
"NET" directory on the C disk, the line might look like this:
DEVICE=C:/NET/NETDISK.SYS CASEY DRZEUS
The two parameters in this example (CASEY and DRZEUS) are the name of this
client PC and the name of the server PC, respectively. Each PC on the LAN
should have a unique name.
Adding a line like the one above to the CONFIG.SYS file will make a new disk
drive letter available to DOS and DOS programs. For example, your PC might
assign drive letter D to the DRZEUS network disk. You could then look at the
root directory of DRZEUS with the DOS command
dir d:
If a client PC will access more than one network disk, then its CONFIG.SYS
file should contain one line for each network disk. Let's expand our example so
that the client PC named CASEY could access the network disks named DRZEUS and
ATHENA.
DEVICE=C:/NET/NETDISK.SYS CASEY DRZEUS
DEVICE=C:/NET/NETDISK.SYS CASEY ATHENA
Configure Server
Download NETDISK.EXE to each PC that will run as a server.
You don't install this program. You simply run NETDISK.EXE whenever you want
a PC to perform the server function, and stop it when you're finished.
NETDISK.EXE requires some parameters, and they must be in the right order. The
syntax can be summarized as follows:
netdisk <Drive> <ServerName> <Options>
<Drive> The drive letter of the disk to be served (i.e. made
available to client PCs). For example, this could be "C".
<ServerName> The name of the server PC. For example, this could be
DRZEUS.
This name should be unique on the LAN.
<Options> Zero or more
of the following options:
/v = Verbose. Causes the server to print
extra status messages.
/w -Write. Lets client PCs write on the disk. Without this option,
client PCs will only be able to read the disk.
/x___ - Security. Lets you specify which PCs can use the disk.
In place of ___ you specify the name of a normal ASCII file. You
can create this file with any text editor (eg EDLIN, PE2, E3). Each line of the
file is either a comment (if the line starts with a space), or names one client
PC who's authorized to use the disk. Lines that are not comments must be in one
of the following formats:
ClientName
ClientName AccessCode
ClientName AccessCode LanID
ClientName LanID
"ClientName" is the name of the client PC."AccessCode" is "R" to restrict
this client to read-only access, or "W" to allow the client read-write access.
If "AccessCode" is not specified, "W" is assumed.
Note that if the"/w"option mentioned above is NOT specified, then NO clients
will be permitted to write on the disk. "LanID" is the unit identification
number of the LAN adapter that the client PC uses to access the server. If you
omit this number, the server will fill it in the first time the client uses the
disk.
Lets see how we might start the NetDisk server program, so that the client
PC we called CASEY could read and write on the server PC's C: disk.
netdisk C DRZEUS /w
Implementation
A brief summary of how NetDisk works follows.
Uses the NETBIOS interface in both the client and server PCs.
Uses interrupts 0x25 and 0x26 to access the disk in the server PC.
Uses the "media changed" mechanism to synchronize the updates that multiple
client PCs could make over a period of time to the same network disk.
Determines which client PCs are active by timeouts.
Checks the identity of client PCs by matching the unit identification number
of their LAN adapter (as returned by the NETBIOS remote adapter status
operation) against the information stored in a security file.
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