ZFS arc behaviour different after upgrading to 10.4

[Ruben van Staveren]

Hi list,

I noticed that the ZFS ARC is behaving differently with 10.4, giving me 
a much worser cache effeciency as with 10.3

The following grafana/telefraph graph illustrates this as follows.

https://snapshot.raintank.io/dashboard/snapshot/X18wHgmqFnMccEYlnbwgQtYgLIZ4oQLU?panelId=65061&fullscreen&orgId=2

Left I'm still running 10.3, Started some maintenance (binary update 
with freebsd-update) at 12:36 and booted into 10.4 at 14:34. Since then 
the ARC hits/misses are much more irregular. Disabling compression 
(apparently also introduced in 10.4) didn't help that much with regards 
to the pattern although it did shave off some load of the system.

Any thoughts on the changed behaviour?

Cheers,
     Ruben

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