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Subject: RE: Unique Channel Names??? -> redundant CA servers
From: Matthias Clausen DESY -MKS-2/KRYK- <[email protected]>
To: [email protected]
Cc: [email protected]
Date: Tue, 9 Mar 1999 9:08:02 +0100 (MET)
>On Monday, March 08, 1999 10:25 AM, John A. Priller [SMTP:[email protected]] wrote:
>> I don't have an answer to that (sorry), but I'd like to add a somewhat
>> related question to the discussion:  I'm using the portable Channel Access
>> Server on Windows NT PCs to add our Modicon/PLC information into the EPICS
>> system.  I have two server PCs, for redundancy, and whenever I launch MEDM
>> or Probe for one of these channels I get the same error message Natalie is
>> getting.  Is there any way of turning this off?
>>
>
>Sorry, you can not have the same PV name in two different CA servers on the same subnet
>in the current and past versions of EPICS unless each of the servers involved is 
>configured to use different port numbers.

Wouldn't it be nice and not too difficult to synchronize two CA servers with the same 
database that way that one of them runs as a primary server while a second one with the 
same database runs as a redundant one?
The beacon of the primary server could disable the answers to CA name requests aa well as 
the beacons of the secondary server. As soon as the primary is dead the secondary will 
take over. CA clients will reconnect the standard way.

This implementation will need some additional environment variables like 
CA_SERVER_REDUNDANT=TRUE
CA_SERVER_PRIMARY=TRUE/FALSE
CA_SERVER_SYNCH_RECORD=record_name ! this record is unique on each of the redundant CA 		
					servers and used to trigger the failover

The necessary implementation could be included in the IOC CA server as well as in the 
portable CA server.
The one who needs it urgently might take the task and implement it... (EPICS answer)

Matthias

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