nixos-conf/shared/hardware/impermanence.nix

{ lib, ... }:
{
  # Default set of directories we always want to persist
  environment.persistence."/persist" = {
    enable = true;
    hideMounts = true;

    files = [
      "/etc/machine-id"
      "/etc/ssh/ssh_host_rsa_key"
      "/etc/ssh/ssh_host_ed25519_key"
    ];

    directories = [
      "/var/lib/systemd/timers"
      "/var/lib/nixos"
      "/var/log"
    ];
  };

  fileSystems."/persist".neededForBoot = true;

  services = {
    fstrimg.interval = "daily";
    zfs = {
      autoScrub.enable = true;
      autoSnapshot = {
        enable = true;
        flags = "-k -p --utc";
      };
      trim.interval = "daily";
    };
  };

  boot.initrd.postResumeCommands = lib.mkAfter ''
    zfs rollback -r zroot/root@blank
    zfs rollback -r zroot/home@blank
  '';
}