Btrfs raid with Disko

First time installing NixOS manually and fully declaratively. Also first time using disko, so i have a few questions i could not find answers for:

  1. if i determine already existing, exactly same partition in Disko, will it reformat disk?
  2. i have a btrfs raid between 2 SSDs (not mdadm), how can i determine this structure in disko configuration?