Hello cephers,

I have a situation where from time to time the write operation to the seph 
storage hangs for 3-5 seconds. For testing we have a simple line like:
while sleep 1; date >> logfile; done &

with this we can see that rarely there are 3 seconds or more differences 
between the consecutive outputs of date.
Initially we have suspected the deep scrub and we have tuned its parameters, so 
right now I'm confident that the reason is something different than the deep 
scrubbing.

I would like to know if any of you has encountered a similar situation, and 
what was the solution for it.
I am suspecting the network between the compute nodes and the storage, but I 
need to prove this. I am thinking on enabling client side logging for librbd, 
but I see there are many subsystems where the logging can be enabled. Can 
anyone tell me which subsystem should I log, and at which level to be able to 
see whether the network is causing write issues?
We're using ceph 0.94.10.

Thank you,
Laszlo
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