I'm trying to use it by the command

pywallet.py --recover --recov_size 30.1Gio --recov_device /dev/sda3 --recov_outputdir /home/jackjack/recovered_wallets

but all I'm getting is

Starting recovery.
Can't open /dev/sda3, check the path or try as root
  Error: (2, 'No such file or directory')

I'm a dunce xd