configuration.nix/system/filesystem.nix

{...}: {
  boot.tmpOnTmpfs = true;
  fileSystems = {
    "/" = {
      device = "tmpfs";
      fsType = "tmpfs";
      options = ["defaults" "uid=0" "gid=0" "mode=0755"];
      neededForBoot = true;
    };
    "/nix" = {
      device = "/dev/vg0/system";
      fsType = "btrfs";
      options = ["subvol=/@nix" "compress-force=zstd"];
      neededForBoot = true;
    };
    "/persist" = {
      device = "/dev/vg0/system";
      fsType = "btrfs";
      options = ["subvol=/@persist" "compress-force=zstd"];
      neededForBoot = true;
    };
    "/mnt/system" = {
      device = "/dev/vg0/system";
      fsType = "btrfs";
      options = ["subvol=/" "compress-force=zstd"];
    };
    "/boot" = {
      device = "/dev/disk/by-partlabel/ESP";
      fsType = "vfat";
    };
  };
}