Re: Network performance checks

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Quoting Massimo Sgaravatto (massimo.sgaravatto@xxxxxxxxx):
> After having upgraded my ceph cluster from Luminous to Nautilus 14.2.6 ,
> from time to time "ceph health detail" claims about some"Long heartbeat
> ping times on front/back interface seen".
> 
> As far as I can understand (after having read
> https://docs.ceph.com/docs/nautilus/rados/operations/monitoring/), this
> means that  the ping from one OSD to another one exceeded 1 s.
> 
> I have some questions on these network performance checks
> 
> 1) What is meant exactly with front and back interface ?

Do you have a "public" and a "cluster" network? I would expect that the
"back" interface is a "cluster" network interface.

> 2) I can see the involved OSDs only in the output of "ceph health detail"
> (when there is the problem) but I can't find this information  in the log
> files. In the mon log file I can only see messages such as:
> 
> 
> 2020-01-28 11:14:07.641 7f618e644700  0 log_channel(cluster) log [WRN] :
> Health check failed: Long heartbeat ping times on back interface seen,
> longest is 1416.618 msec (OSD_SLOW_PING_TIME_BACK)
> 
> but the involved OSDs are not reported in this log.
> Do I just need to increase the verbosity of the mon log ?
> 
> 3) Is 1 s a reasonable value for this threshold ? How could this value be
> changed ? What is the relevant configuration variable ?

Not sure how much priority Ceph gives to this ping check. But if you're
on a 10 Gb/s network I would start complaining when things take longer
than 1 ms ... a ping should not take much longer than 0.05 ms so if it
would take an order of magnitude longer than expected latency is not
optimal.

For Gigabit networks I would bump above values by an order of magnitude.

Gr. Stefan

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