create crush rule <name> to start from <root>,
replicate across buckets of type <type>, using
a choose mode of <firstn|indep>
+ -i mapfn --create-replicated-rule name root type
+ create crush rule <name> to start from <root>,
+ replicate across buckets of type <type>
+ --device-class <class>
+ use device class <class> for new rule
-i mapfn --remove-rule name
remove the specified crush rule