Columns: rrddata:var1:metric1.max:start:end:step rrddata:var2:metric2.max:start:end:step

or

Columns: rrddata:m1:fs_used.max,1,*:1614839543:1614929543:1

With "1,*" you can rescale high values. This is only needed for high values like MB. 
You can rescale such values with "1024,*" or "1024,/"