I recently started a process of using rbd snapshots to setup a backup regime 
for a few file systems contained in RBD images.  While this generally works 
well at the time of the snapshots there is a massive increase in latency (10ms 
to multiple seconds of rbd device latency) across the entire cluster.  This has 
flow on effects for some cluster timeouts as well as general performance hits 
to applications.

In research I have found some references to osd_snap_trim_sleep being the way 
to throttle this activity but no real guidance on values for it.   I also see 
some other osd_snap_trim tunables  (priority and cost).

Is there any recommendations around setting these for a Jewel cluster?

cheers,
 Adrian

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