Argonne National Laboratory

Experimental Physics and
Industrial Control System

1994  1995  <19961997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  2017  2018  2019  2020  Index 1994  1995  <19961997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  2017  2018  2019  2020 
<== Date ==> <== Thread ==>

Subject: Re: fallback CA servers?
From: Jeff Hill <johill@lanl.gov>
To: William Lupton <wlupton@keck.hawaii.edu>
Cc: tech-talk@aps.anl.gov
Date: Fri, 03 May 1996 10:26:13 -0600
William Lupton wrote:
> 
> Dear all,
> 
>   We are discussing how to handle simulation both when IOCs are present and
> when they are absent. For simulation at other sites we are writing a Unix
> CA server which emulates part of our VME database. For simulation at the
> telescope we are toying with the idea that we might run the Unix CA server
> all the time but that connections to it would only be used when the vxWorks
> CA server was not running.
> 
>   This raised the question of whether anyone has ever discussed implementing
> "fallback" CA servers which would automatically be used (perhaps only for
> gets?) if the "master" server failed. At the CA server level it would imply
> that the server had an associated priority level. At the CA client level,
> multiple responses to ca_search() would have to make use of the priority
> level to decide which server to connect to, and connection state change
> could cause server rollover.
> 

Tate - one of the industrial partners - has a version of EPICS which
supports dual redundant IOCs. If one IOC fails the other IOC detects it and
control of the IO is switched over to the properly functioning IOC.

I agree with Steven Beard that we would need to be careful that the
operator isnt mislead to think he is controlling the operational
system when in fact he is still attached to the simulation server.

I think the idea of a backup server that tracks the values in the
operational system is an interesting idea. The backup/simulation
server would need to receive proper notification when the master is ok.
Presumably the backup server would then disconnect its clients and the
clients would then reattach to the master.

Support for this would require changes to the CA protocol I suspect.

Jeff


References:
fallback CA servers? William Lupton

Navigate by Date:
Prev: Re: simple questions Marty Kraimer
Next: Re: simple questions Jeff Hill
Index: 1994  1995  <19961997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  2017  2018  2019  2020 
Navigate by Thread:
Prev: Re: fallback CA servers? Steven M Beard
Next: Re: fallback CA servers? Andrew Johnson
Index: 1994  1995  <19961997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  2017  2018  2019  2020 
ANJ, 10 Aug 2010 Valid HTML 4.01! · Home · News · About · Base · Modules · Extensions · Distributions · Download ·
· Search · EPICS V4 · IRMIS · Talk · Bugs · Documents · Links · Licensing ·