perfSONAR User Q&A and Other Discussion

["Andrew Lake" <>]

Comments inline. I also created an issue to add some notes on your questions to docs.perfsonar.net. 

I have a couple of questions about the use of a central Measurement
Archive, as documented at http://docs.perfsonar.net/multi_central_MA.html

1. It seems this is a "push" architecture, i.e. the perfsonar node which
made a measurement connects to the central MA to store the results there.

What happens if the central MA goes down for a while, or the network to
the central MA? Are the measurements lost, or are they buffered to be
delivered later? Does this have any effect on the timing of subsequent
measurements?

If the host MA goes down, the missed measurements are stored on local disk under /var/lib/regular_testing and the regular_testing daemon tries to register them when the MA comes back. If the MA is down too long though (where “too long” varies on the system and number of tests being run) the backlog of tests can get too big and regular-testing can’t catch-up. On a Toolkit installation, we actually clean out the backlog of tests for this reason as we have frequently seen hosts get in a state where the backlog of tests is too big.

What if there are multiple MAs selected, but only one is down or
unreachable?

Each MA will be treated the same as if they were the only MA in the file. In other words, the one that is up will get the data and a backlog will be kept on disk for the one that is down. When the downed MA comes back up the daemon will try to register the old data points (subject to the limitations of my previous comment). 

2. If you have made manual changes to regular_testing.conf to point to a
different MA (or multiple MAs), and you subsequently change test
configurations through the GUI, does this leave your MA customisations
alone? 

Yes. The GUI leaves all measurement_archive blocks alone.

 

Thanks,

Brian Candler.