disko configuration that i wrote recently but haven't used to reformat my in-use disk (because i haven't bothered migrating) is:

let
  # mkSubvolumes is a helper function to define BTRFS subvolumes from a list
  # of strings (representing the path the subvolume will be mounted at, and
  # using that as the name)
  mkSubvolumes = paths: builtins.listToAttrs (map (p: {
    name = p;
    value = {
      mountpoint = if p == "/root" then "/" else p;
      mountOptions = [ "defaults" "ssd" "compress=zstd:3" "noatime" ];
    };
  }) paths);
in
{
  disko.devices = {
    system = {
      device = "/dev/disk/by-id/...";
      type = "disk";

      content = {
        type = "gpt";

        partitions = {
          ESP = {
            size = "1024M";
            type = "EF00";
            content = {
              type = "filesystem";
              format = "vfat";
              mountpoint = "/boot";
              mountOptions = [ "umask=0077" ];
            };
          };

          luks = {
            size = "100%";
            content.type = "luks";
            content.name = "system";
            content.settings.allowDiscards = true;

            # use a fido2 key for unlocking
            content.enrollFido2 = true;

            # do not generate a recovery passphrase (i manually add additional fido keys)
            content.enrollRecovery = false;

            content.content = {
              type = "btrfs";

              subvolumes = mkSubvolumes [
                "/nix"
                "/persist"
                "/root"
                "/var/log"
                "/home"
              ] // {
                "/swap" = {
                  mountpoint = "/swap";
                  swap.swapfile.size = "72G";
                  swap.swapfile.path = "file"; # relative path, results in /swap/file
                };
              };

              # This hook creates a snapshot of the root subvolume after it is
              # created (and critically, empty), which is used for automatic
              # rollback on startup. see //system/modules:impermanence.nix for
              # more information about that process.
              postCreateHook = ''
                set -eufo pipefail
                MOUNTPOINT=$(mktemp -d)
                mount --type btrfs \
                  --options defaults,ssd,noatime,subvol=/ \
                  /dev/mapper/system \
                  "$MOUNTPOINT"
                trap 'umount "$MOUNTPOINT"; rm -rf "$MOUNTPOINT"' EXIT
                btrfs subvolume snapshot -r \
                  "$MOUNTPOINT/root" "$MOUNTPOINT/root-blank"
              '';
            };
          };
        };
      };
    };
  };
}

you can also do this using btrfs native multi-disk support

this is how i'll be migrating this machine's disk to a new disk, with the above disko configuration. btrfs send :)

my impermanence module (referenced in the above config) just sets up the boot.initrd.systemd.services.rollback unit that handles deleting the root subvol and rolling back from the snapshot, and contains my environment.persistence."/persist" configuration (and other stuff necessary to handle w/ impermanence.

i'd be interested in seeing your crash recovery setup.

my impermanence module (referenced in the above config) just sets up the boot.initrd.systemd.services.rollback unit that handles deleting the root subvol and rolling back from the snapshot, and contains my environment.persistence."/persist" configuration, and other stuff necessary to handle w/ impermanence.

i'd be interested in seeing your crash recovery setup.

my impermanence module (referenced in the above config) just sets up the boot.initrd.systemd.services.rollback unit that handles deleting the root subvol and rolling back from the snapshot, contains my environment.persistence."/persist" configuration, and other stuff necessary to handle w/ impermanence.

i'd be interested in seeing your crash recovery setup.

        btrfs subvolume delete /mnt/root

        btrfs subvolume snapshot /mnt/root-blank /mnt/root

this snippet is from the systemd unit that runs in initrd before sysroot, and just unconditionally deletes the subvol and restores it from the blank snapshot (this is taken at disk formatting time; the above disko config handles this with a postCreateHook)

see also:

• https://search.nixos.org/options?channel=unstable&query=postResume#show=option%253Aboot.initrd.postResumeCommands
• https://search.nixos.org/options?channel=unstable&query=postDevice#show=option%253Aboot.initrd.postDeviceCommands