Re: n+2:1 Protection Parity Calc
I gave up tracking disk usage down to single kilobytes after plotting some result from a real cluster...
It was a very "interesting" chart and I would recommend to the experiment by yourself (I haven't kept it).
Practical rule of thumb (for a 3 node cluster):
files up to 128 KB use 3x,
files of 512 KB or multiples of 512 KB use 2+1 which means factor 1.5x -- maximum efficiency for 3 nodes
files between 128 and 512 KB gradually gain efficiency from 3x to 1.5x
files slightly larger than 512 KB loose a bit of efficiency again
files much larger than 512 KB essentially use 2+1 or 1.5x
Again, do some tests and plot the data!