Hi! I'm also struggling with a Disko/ZFS issue.

I've set options.mountpoint = "legacy".
But when I zfs list the dataset, I don't see legacy in the datasets mountpoint attribute?
What am I doing wrong?

$ nix eval .#nixosConfigurations.nas-2024.config.disko.devices.zpool.nvmepool.datasets."root/nix".options
{ mountpoint = "legacy"; }

$ nix eval .#nixosConfigurations.nas-2024.config.disko.devices.zpool.nvmepool.datasets."root/nix".mountpoint
"/nix"

# on nas-2024 during emergency boot mode
$ zfs list nvmepool/root/nix
NAME                        USED  AVAIL  REFER  MOUNTPOINT
nvmepool/root/nix    XXX    YYY     ZZZ      /nix

My config matches AFAICT this post by ElvishJerrico: https://discourse.nixos.org/t/disko-and-zfs-emergency-mode-during-boot/58138/8

Couple of questions about NixOS live USBs:

I want to partition my 64 GB USB flash drive into two partitions (FAT32 live USB + ext4 storage), so I used the following disko config:

let
  usb = "/dev/disk/by-id/usb-USB_SanDisk_3.2Gen1_0401a943ae4197a38a6f9070194e9ea2b3fb8dbb7997e05ed1b197c0e28946be4b8f000000000000000000001cf4be6800926418a955810751ab6336-0:0";
in {
  disko.devices = {
    disk = {
      live = {
        type = "disk";
        device = usb;
        content = {
          type = "gpt";
          partitions = {
            ESP = {
              type = "EF00";
              device = "${usb}-part1";
              priority = 0;
              size = "8192M";
              content = {
                type = "filesystem";
                format = "vfat";
              };
            };
            storage = {
              device = "${usb}-part2";
              priority = 1;
              size = "100%";
              content = {
                type = "filesystem";
                format = "ext4";
              };
            };
          };
        };
      };
    };
  };
}

I then copied over the files from the (minimal, non-graphical) NixOS live ISO into partition 1, hoping that the instructions on the Arch wiki would generalize to NixOS, but then my live ISO gets stuck with the following error message:

[...]
Timed out waiting for device /dev/root, trying to mount anyway
mounting /dev/root on /iso...
mount: mounting /dev/root on /mnt-root/iso failed: No such file or directory

An error occurred [...]

How can I use my USB flash drive as both a live USB and as a storage device? I found this relevant Discourse link but there was no resolution to the problem there.

I realize this might not be the best place to ask this, but I figured that folks here would have expertise configuring boot partitions correctly.

Couple of questions about NixOS live USBs:

I want to partition my 64 GB USB flash drive into two partitions (FAT32 live USB + ext4 storage), so I used the following disko config:

let
  usb = "/dev/disk/by-id/usb-USB_SanDisk_3.2Gen1_0401a943ae4197a38a6f9070194e9ea2b3fb8dbb7997e05ed1b197c0e28946be4b8f000000000000000000001cf4be6800926418a955810751ab6336-0:0";
in {
  disko.devices = {
    disk = {
      live = {
        type = "disk";
        device = usb;
        content = {
          type = "gpt";
          partitions = {
            ESP = {
              type = "EF00";
              device = "${usb}-part1";
              priority = 0;
              size = "8192M";
              content = {
                type = "filesystem";
                format = "vfat";
              };
            };
            storage = {
              device = "${usb}-part2";
              priority = 1;
              size = "100%";
              content = {
                type = "filesystem";
                format = "ext4";
              };
            };
          };
        };
      };
    };
  };
}

I then copied over the files from the (minimal, non-graphical) NixOS live ISO into partition 1, hoping that the instructions on the Arch wiki would generalize to NixOS, but then my live ISO gets stuck with the following error message:

[...]
Timed out waiting for device /dev/root, trying to mount anyway
mounting /dev/root on /iso...
mount: mounting /dev/root on /mnt-root/iso failed: No such file or directory

An error occurred [...]

How can I use my USB flash drive as both a live USB and as a storage device? I found this relevant Discourse link but there was no resolution to the problem there.

I realize this might not be the best place to ask this, but I figured that folks here would have expertise configuring boot partitions correctly.

For reference, the NixOS manual says I should dd the ISO to the disk directly: sudo dd if=<path-to-image> of=/dev/sdX bs=4M conv=fsync

In reply to @tim92:matrix.org
I don't think that this will work since you need to unmount the live USB to format it as storage device

Soooo,
I have decided to just try it.
After debugging some syntax issues, I have encountered this bug:

error:
       … while evaluating the attribute 'diskoScript'

         at /nix/store/3mlzsgflq3z4wsk2arffhd999h1hj17g-disko/share/disko/lib/default.nix:418:15:

          417|
          418|               diskoScript = (diskoLib.writeCheckedBash { inherit pkgs checked; }) "disko" ''
             |               ^
          419|                 export PATH=${lib.makeBinPath ((cfg.config._packages pkgs) ++ [ pkgs.bash ])}:$PATH

       … in the condition of the assert statement

         at /nix/store/y11h0vfmjaf8j1796x0n2454hqldnbbr-0vyi8f8l8cya10dmgfrj0df2iqxlhiyi-source/pkgs/build-support/writers/scripts.nix:32:5:

           31|     assert (types.path.check nameOrPath) || (builtins.match "([0-9A-Za-z._])[0-9A-Za-z._-]*" nameOrPath != null);
           32|     assert (types.path.check content) || (types.str.check content);
             |     ^
           33|     let

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: The option `disko.devices.disk.lvm_vg.root_vg' does not exist. Definition values:
       - In `<unknown-file>':
           {
             lvs = {
               games = {
                 content = {
                   extraArgs = [
           ...

Does anybody have any idea how I can fix this?

Here's my disko.nix:

{
disko.devices = {
	disk = {
		disk0 = {
			type = "disk";
			device = "/dev/nvme1n1";
			content = {
				type = "gpt";
				partitions = {
					esp = {
						name = "ESP";
						size = "500M";
						type = "EF00";
						content = {
							type = "filesystem";
							format = "vfat";
							mountpoint = "/boot";
						};
					};

					root = {
						name = "root0";
						size = "100%";
						content = {
							type = "lvm_pv";
							vg = "root_vg";
						};
					};
				};
			};
		};
		disk1 = {
			type = "disk";
			device = "/dev/nvme0n1";
			content = {
				type = "gpt";
				partitions = {
					root = {
						name = "root1";
						size = "100%";
						content = {
							type = "lvm_pv";
							vg = "root_vg";
						};
					};
				};
			};
		};

		lvm_vg = {
			root_vg = {
				type = "lvm_vg";
				lvs = {
					root = {
						size = "25%FREE";
						content = {
							type = "btrfs";
							extraArgs = ["-f"];
							subvolumes = {
								"/root" = {
							 	 mountpoint = "/";
								};

								"/persist" = {
								mountOptions = ["subvol=persist" "noatime"];
								mountpoint = "/persist";
								};

								"/nix" = {
								mountOptions = ["subvol=nix" "noatime"];
								mountpoint = "/nix";
								};
							};
						};
					};

					games = {
						size = "100%FREE";
						content = {
							type = "btrfs";
							extraArgs = ["-f"];
							subvolumes = {
								"/games" = {
								mountOptions = ["subvol=games" "noatime"];
								mountpoint = "/games";
								};
							};
						};
					};
				};
			};
		};
	};
};
}