[gpfsug-discuss] How Zimon/Grafana-bridge process data

[Dorigo Alvise (PSI)]

Hi,
I've a GL2 cluster based on gpfs 4.2.3-6, with 1 support node and 2 IO/NSD nodes.

I've the following perfmon configuration for the metric-group GPFSNSDDisk:

{
        name = "GPFSNSDDisk"
        period = 2
        restrict = "nsdNodes"
},

that, as far as I know sends data to the collector every 2 seconds (correct ?). But how ? does it send what it reads from the counter every two seconds ? or does it aggregated in some way ? or what else ?

In the collector node pmcollector, grafana-bridge and grafana-server run.

Now I need to understand how to play with the grafana parameters:
- Down sample (or Disable downsampling)
- Aggregator (following on the same row the metrics).

See attached picture 4s.png as reference.

In the past I had the period set to 1. And grafana used to display correct data (bytes/s for the metric gpfs_nsdds_bytes_written) with aggregator set to "sum", which AFAIK means "sum all that metrics that match the filter below" (again see the attached picture to see how the filter is set to only collect data from the IO nodes).

Today I've changed to "period=2"... and grafana started to display funny data rate (the double, or quad of the real rate).

I had to play (almost randomly) with "Aggregator" (from sum to avg, which as fas as I undestand doesn't mean anything in my case... average between the two IO nodes ? or what ?) and "Down sample" (from empty to 2s, and then to 4s) to get back real data rate which is compliant with what I do get with dstat.

Can someone kindly explain how to play with these parameters when zimon sensor's period is changed ?

Many thanks in advance
Regards,

   Alvise Dorigo
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