If you want to start out with your own module and just need a solution specifically to add zfs datasets, it might be helpful to know about

nixosConfigurations.$hostname.config.disko.devices.zpool.$poolname.datasets."$dataset"._create which gives you the command diskos formatScript would use to create the dataset. That's already idempotent. Sylvie (she/it) 🏳️‍⚧️

In reply to @phaer:matrix.org

Yes, it's just for initial setup by default.

If you feel adventurous and have a tested backup of your data you can try rerunning the system.build.formatScript which should be idempotent but please review the script and don't blame us if it eats your data 😇

fileSystems."/nix" = {
	device = "/persist/nix";
	fsType = "none";
	options = [ "bind" ];
	depends = [ "/persist" ];
	neededForBoot = true;
};

fileSystems."/nix" = {
	device = "/persist/nix";
	fsType = "none";
	options = [ "bind" ];
	depends = [ "/persist" ];
	neededForBoot = true;
};