Experimental Physics and
Industrial Control System

Michael Borland <[email protected]> · Wed, 17 Nov 1999 10:28:32 -0600 (CST)

At APS we use SDDS tools for rates up to 30Hz in various ways.  It
depends on the tool you choose, how many PVs you want to log,
etc.
* sddsmonitor, sddslogger
	Typically used for logging at 1Hz or slower.
	For < ~100 PVs one can do 20-25Hz, depending on the
	network traffic and how busy the IOCs are.
* sddsmonitor glitch mode
	Typically we do 4Hz for ~1000 PVs into a circular buffer,
	which is dumped when something "bad" happens.
* sddssynchlog
	Used for synchronized logging at high rates.  We use
	it on our linac for 30Hz synchronized acquisition but not
	for archival work.  I haven't tried past 30Hz as our linac
	doesn't run any faster.

One should distinguish between the particular applications and the SDDS
approach.  There is nothing in the SDDS approach that forbids high data
rates.  We just haven't had much need for it.  I tend to find that high
data rates are limited more by network traffic or IOC load than anything
on the workstation end.

As for practicality of storing large amounts of data, that was never a
problem with SDDS.  APS has >26GB of archival data stored as SDDS files,
going back to the project inception in 1995.  About 22k PVs are archived
in this fashion.

For more information see "SDDS:  A Modular Toolkit for Accelerator
Simulation, Control, and Operation" at
http://www.aps.anl.gov/asd/oag/oagTalks.shtml 

--Michael Borland

>........ I was under the impression
>that the SDDS data logging facility was somewhat rate limited to
>1 Hz and that it was impracticle for saving Giga bytes of data over
>long periods of time. Is this so? .......
>
>Could someone please clarify the data rates for SDDS logging?
>
>	Thanks,
>	Bob

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System