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<== Date ==> <== Thread ==>

Subject: Re: PV save and restore tool sought
From: Tim Mooney <[email protected]>
To: Emmanuel Mayssat <[email protected]>
Cc: Thomas Birke <[email protected]>, [email protected]
Date: Tue, 31 Jul 2007 15:28:25 -0500
Emmanuel Mayssat wrote:
On Fri, 2007-06-29 at 16:55 +0200, Thomas Birke wrote:
The warm-reboot save-and-restore is realized with the IOC-based version of autosave as it comes with the synApps package.

I am currently investigating warm reboot. As such, I am currently investigating autosave and may move away from that feature implementation in the driver.

My questions are: * Is autosave the mainstream tool? i.e. the bumpless utility used by
most of you? I heard at SLAC, they are using channel watcher.
http://www.slac.stanford.edu/comp/unix/package/epics/extensions/ChannelWatcher/index.html
Is there anything else that you recommend I look at?


* What are autosave's and your recommended software's limitations? what
happens in a case of a ioc crash? can backup files be corrupted? Are
backups saved in files or database? Are files the most simple and
reliable architecture? what are the disadvantage/advantages of a
distributed database? central database?
When an ioc crashes, one of autosave's files can be corrupted, but it should not
be possible to have both corrupted by a crash (or a reboot) during a file write.
However, if the file server says a file is secure, and it's not actually secure (e.g.,
it hasn't actually been written to disk) then autosave can end up with both copies
corrupted. If this is a possibility, one should specify that multiple copies of the
save file be written.


I don't know if files are the simplest and most reliable architecture, but if they
don't work, lots of other things also don't work.


* What are the disadvantages/advantages of ioc-based backup utility
versus others designed as ca-client? I read "The current version of Save/Restore (sr), also known as Bumpless
Reboot, may be interfering with normal IOC operations due to the large
number of file writes." How much of a problem is that, really?
One advantage of an IOC-based autosave is that it can easily be made to start
automatically whenever the IOC boots up.


A disadvantage of this particular backup utility is that it overwrites the entire
save file if any PV in the file has changed. At one point this was a generic
limitation of least-common-denominator IOC software (vxWorks netDrv
did not permit random access to a file). But now, since autosave requires NFS,
it's just an annoying holdover that should be fixed.
* Is there a SIMPLE way to generate a req/request file on the fly for
backup? I have "dynamic" ioc, where the names of records may change
between reboots, or some records may just disappear. Do you have each
time to reconfigure the backup request file? Although I believe this
should be required for a general backup utility, why should it for a
bumpless reboot utility?
The list of PV's to be saved does not automatically configure itself to match
PV's actually loaded. Autosave tolerates missing PV's, but if PV's come and
go, their old values will not automatically be restored when they come back.
Is it possible to generate a req file at ioc startup that save all the
"live" records with name's ending with *O or *AO, etc. ( a dbgrep to a
file can help, but the backup utility needs to reread its config files )
Yes, but autosave doesn't provide much help. If you have a generic request file
for each record type, listing the PV's that should be managed for that record type,
you could use autosave's include-file capability to help with the job.
* What happens if the backup utility is looking for a record that
doesn't exist? Is backup still ongoing? Does it significantly increase
the traffic load on the network?

Autosave doesn't kill itself if it can't find a PV. It's just a CA client, so its effect
on the network when PV's are not found is the same as any other CA client.
* Is log-on-change possible for individual output records? I heard this
is not the forte of autosave, but I may be wrong.

Autosave doesn't log anything. It maintains only the most recent value.
* What if there are no values previously saved on the particular ioc.
What is the default value? The one in db file? Is it possible to
import/copy backup data?


If autosave has no value to restore, it will simply not restore, so the value in the
database is used.
* Although I am mostly interested in bumpless reboot, are there
utilities that do bumpless reboot in a very similar way they do regular
backup? I am currently using sddscasr (casr in sdds files ), but am
reacquainting myself with casr and burt. Should I look at those or are
they deprecated? Should I look at any other applications?

I don't know whether casr and burt are still being maintained. Any client that
can write a file can cause autosave to have that file restored at boot time.
Autosave's save and restore operations are separately configured, so it can
restore files that it did not save, and save files that it will not restore.
* etc.


-- Emmanuel



--
Tim Mooney ([email protected]) (630)252-5417
Beamline Controls & Data Acquisition Group (www.aps.anl.gov/aod/bcda)
Advanced Photon Source, Argonne National Lab


References:
PV save and restore tool sought Rock, Judith E.
Re: PV save and restore tool sought Thomas Birke
Re: PV save and restore tool sought Emmanuel Mayssat

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