Compatibility Statement 
Nonstop Networks Limited's No*Stop* Network v3.0 is compatible with LANtastic 
NOS v4.xx and v5.xx running with MS-DOS 3.3 or higher.

Product Overview
No*Stop* Network protects against server failures, disk medium failures and 
workstation to file server cabling failures (assuming a good connection still 
exists between the workstation and the backup server) by duplexing file 
accesses on a server (the primary server) to the backup server (the secondary 
server).  This mechanism, also known as fault tolerance (level 3) is a good 
way of providing on-line backup.  The system also provides the system 
administrator options to specify site-specific text to be displayed as part 
of the failure notification message.  For applications which run unattended 
and do not have a user available to respond to failure notifications, the 
notification messages can be redirected to a file and operation will be 
continued without interruption.

Product Installation Notes
To start with, you will need to pair up logical drives to be duplexed, or 
mirrored.  Primary:secondary drive pair can be specified at install time (by 
NNSETUP) or through the NNDRVPR utility.  Both the primary and the secondary 
drives can be a local DOS drive, a local directory or a network drive or 
directory.
Suppose x: is chosen as the primary drive and y: the secondary drive.  The 
second step is to synchronize the pair so that the secondary drive is a valid 
mirror of the primary.  Synchronization can be carried out by the RECOVERY 
utility to restore contents of the primary drive to the secondary drive.  To 
invoke drive mirroring, simply load the NETWORK TSR:
	C:> NETWORK ON (drive,drive)...(drive,drive)
		as in:
	C:> NETWORK ON (X,Y)
The NETWORK TSR requires 10K - 15K RAM and can be turned off by typing 
'NETWORK OFF'.  Batch files to load and unload the TSR with user-specific 
drive pairs can be created easily by the user.
Under DOS, each open file requires either a File Control Block (FCB) or a 
File Handle of its own.  No*Stop* Network, in its mirroring capacity, 
requires an extra FCB or handle for each open file which is being mirrored.  
It manages all of the secondary FCBs and handles internally, and by default, 
it provides for 40 FCBs and 125 handles.  If you believe that your system 
requires fewer or more FCBs or handles, you can override the default 
parameters on the command line of the NETWORK TSR.  In addition, if an 
application requires 20 handles without NETWORK, it will now need 40 because 
the 20 files will be mirrored.  As a result, the "FILES=" parameter in 
CONFIG.SYS or in your LANtastic server needs to be increased accordingly.

Product Execution Notes
In the event of a drive failure, a window will appear on the workstation 
screen bearing this notification message:
	CRITICAL ERRORS on DRIVE X:      NO*STOP
	D - Drop this drive and continue
	A - Abort the calling program
	R - Retry this operation
		PLEASE ENTER OPTION: _
To continue, the user must select D, A or R, and may then continue without 
backup, halt processing, or retry.  A similar message will also appear if a 
secondary drive fails.

Additional Considerations
1.      This approach to level 3 fault-tolerance is workstation-based, rather 
than server-based.  A given drive pair exists only in a logical sense on the 
workstation from which NETWORK was invoked.  Each workstation on a network 
can have its own set of pairs, completely different from the others.  Several 
servers can be mirrored to one server, or one server to many servers.  
2.      NETWORK mirrors in only one direction - from the primary logical 
drive to the secondary logical drive.  Direct access to the secondary drive 
will put the drive pair out of synch, and is thus not recommended.
3.      Applications which make direct NETBIOS calls (which do not go through 
DOS logical drives) will not have that activity mirrored.  This may lead to 
unpredictable effects, including data corruption.
4.      Since No*Stop* Network writes to 2 disks instead of 1 (and the backup 
may be across the network), a small performance tradeoff should be expected. 
5.      If continuation of application processing is desired after a drive 
failure, it is necessary to mirror the application programs as well as the 
data files.  This may be tricky, taking into consideration the licensing 
issues and that the application may create server-unique data and/or 
structures.  For example, the license count directory for Lotus 1-2-3 needs 
to be mirrored as well as the program directory.  In addition, whatever 
tricks that apply to mirrored installation of an application apply to 
recovery as well.
6.      Failure notification messages may have problems popping up on the 
screen under certain applications, especially in Windows environment.  It 
will look to the user that the workstation is hanging.  Please refer to the 
No*Stop* Network manual for operational tips under Windows.
7.      It is recommended that Nonstop Networks Limited be consulted about 
whether a certain application will operate smoothly when NETWORK is running.  
Tips for running with quite a few applications including Wordperfect, Lotus 
1-2-3, etc. have been included in the No*Stop* Network manual.  

Version History
12/15/92: No*Stop Network v3.0 tested for compatibility with LANtastic v4.1.
04/04/93: No*Stop Network v3.0 tested for compatibility with LANtastic v5.0.

Vendor Information
Nonstop Networks Limited
311 Turner St., Utica  NY 13501
Phone (212)481-8488   

COMPATIBILITY BULLETIN
Fault Tolerance Subsystems: No*Stop Network 
NOSTOP
 7/17/93
Page 3 of 3




ARTISOFT, Inc. makes no warranties as to the completeness or accuracy of this document.  LANtastic is 
a trademark of ARTISOFT, Inc.  Brand names, company names, and product names are trademarks or 
registered trademarks of their respective companies.


	

	
ARTISOFT, Inc. makes no warranties as to the completeness or accuracy of this document.  LANtastic is 
a trademark of ARTISOFT, Inc.  Brand names, company names, and product names are trademarks or 
registered trademarks of their respective companies.



