Terminal to Server Network Based Fault Tolerance
 
      		**** Cancel to Return ****

Primary File Server FAILS and Backup takes OVER:

1. At the work station acting as terminal and backup server, a ‘Start Backup’, ‘Retry’ notation dialog will appear (10-20 sec delay).
2. If operator selects ‘Start Backup’, the file server program (SNC_TS) will execute on this computer and assume the network functions.
3. If operator selects ‘Retry’, the local terminal will continue to attempt communications with the primary server.
4. What happens when the Backup becomes the file server:

	A. The electronic journal (ORDER.QUE) is moved from the         	recovery directory (RunDir) with the active databases POS-R 	& SKU-R.  These data files contain current information 	collected as the system runs.

	B. Other network terminals connect to the new file server.  A 	control file (F_S.Doc) specifies the server fallback list.  Each 	terminal in the network cycles throw this list attempting to 	connect to an active server in the list.  If the backup lists is 	not available (no redundancy), the name of the primary 	server makes up the list.

Primary Server Returns to Service:

1. At the primary file server, execute the server program (SNC_TS).
2. If the backup file server is running, the primary server will terminate the backup server and itself start execution.
3. What happens when the primary server resumes service:

	 A. The electronic journal and active database files 	(ORDER.QUE, POS-R, SKU-R) are moved from the backup 	server to the primary and stored in the POS directory of the 	main server.

	B. The primary server then takes over as the active server.  	Terminal on the network will connect to the new server as 	they cycle through the fallback list (F_S.Doc).

	C. The terminal that has been running as a terminal and 	backup server once again begins collecting current data and 	acting as an input station (POS Terminal).

HOW to Setup Redundancy:

1. The authorization key on the Backup work station/terminal must be keyed for ‘Backup’.  All other procedures are automatic and self -prompting.  An operator must make the decision to go to backup and to return to the primary server.
 
Cautions:

a.	Going from backup to primary let the primary terminate operation of the backup server.  The primary will then know to move the active data from the backup to the primary.  Data can be lost if the backup server is manually taken down without intervention of the primary server program.
b.	If the backup server is taken up and down after it is established as a server, it will use data stored in its POS directory and will not loss data.
c.	Peripheral functions normally run on a server will have to be configured for the backup server.  Examples of these functions would be credit card processing and remote printer routing.