raidz-calc

.gitignore

*.hi
*.o
/calc

calc.hs

import Control.Applicative ((<$>))
import Text.Printf (printf)
import Control.Monad (when)
import System.IO (hFlush, stdout)

prompt :: String -> IO Integer
prompt str = do
    putStr $ "Input " ++ str ++ ": "
    hFlush stdout
    read <$> getLine

ceilDiv :: Integer -> Integer -> Integer
ceilDiv a b = (a + b - 1) `div` b
infixl 7 `ceilDiv`

main = do
    blocks <- prompt "recordsize / blocksize (typically 32 or 256)"
    raidz_level <- prompt "raidz level (1/2/3)"
    when (raidz_level < 1 || raidz_level > 3) $ fail "bad raid level"
    disks <- prompt $ "disks (at least " ++ show (raidz_level + 1) ++ ")"
    when (disks <= raidz_level) $ fail "bad disks"
    let effect_disks = disks - raidz_level
        rows = blocks `ceilDiv` effect_disks
        needed_blocks' = rows * raidz_level + blocks
        needed_blocks = needed_blocks' `ceilDiv` (raidz_level + 1) * (raidz_level + 1)
        actual_ratio = fromIntegral blocks / fromIntegral needed_blocks :: Double
        ideal_ratio = fromIntegral (disks - raidz_level) / fromIntegral disks :: Double
        relative_ratio = (ideal_ratio - actual_ratio) / ideal_ratio
    printf "Actual ratio: %.3f%%\n" (actual_ratio * 100) 
    printf "Relative ratio loss: %.3f%%\n" (relative_ratio * 100)