How to actually describe MBR partition table?

[RadxaYuntian]

Amlogic based devices must use MBR partition table, as their bootloader will overlap with GPT partition table. However, when I used type = "table", I got the infamous read-only error. What option do I have here?

(Yes this layout is mirroring GPT EFI layout because U-Boot will boot EFI bootloader found on a MBR disk.)

{
  disko.devices = {
    disk = {
      main = {
        device = "/dev/disk/by-id/TARGET-DEVICE";
        type = "disk";
        content = {
          type = "table";
          format = "msdos";
          partitions = [
            {
              name = "ESP";
              start = "16M";
              end = "516M";
              bootable = true;
              content = {
                type = "filesystem";
                format = "vfat";
                mountpoint = "/boot";
              };
            }
            {
              name = "root";
              start = "516M";
              end = "100%";
              content = {
                type = "filesystem";
                format = "btrfs";
                mountpoint = "/";
                mountOptions = [ "compress=zstd" ];
              };
            }
          ];
        };
      };
    };
  };
}

[ppenguin]

I'm in a similar boat, but not with Uboot, but just an old BIOS (HP Microserver Gen8) where I want to use disko but need to use legacy partition for boot too.

[Mic92]

Does maybe hybrid gpt works? https://github.com/nix-community/disko/blob/a08bfe06b39e94eec98dd089a2c1b18af01fef19/example/hybrid-mbr.nix#L21C37-L21C41

[ppenguin]

Does maybe hybrid gpt works? https://github.com/nix-community/disko/blob/a08bfe06b39e94eec98dd089a2c1b18af01fef19/example/hybrid-mbr.nix#L21C37-L21C41

@Mic92 Thanks for chiming in so (very!) fast 😉

Would I still need this one in that case (I suppose it's the "container" for the hybrid attribute?) and would it be ok to make it "symbolic" size (say 1M)? I guess the initrd and kernel will be on the separate /boot anyway?

[altsalt]

I was able to install on non-EFI hardware by specifying a boot partition of type "EF02" and setting boot.loader.grub.efiSupport = false.

Here's the disko-config file

{
  disko.devices = {
    disk = {
      main = {
        device = "/dev/vda";
        type = "disk";
        content = {
          type = "gpt";
          partitions = {
            boot = {
              size = "1M";
              type = "EF02"; # for grub MBR
            };
            root = {
              end = "-1G";
              content = {
                type = "filesystem";
                format = "ext4";
                mountpoint = "/";
                mountOptions = [
                  "defaults"
                ];
              };
            };
            swap = {
              size = "100%";
              content = {
                type = "swap";
                discardPolicy = "both";
                resumeDevice = true; # resume from hiberation from this device
              };
            };
          };
        };
      };
    };
  };
}

[Mic92]

Does maybe hybrid gpt works? https://github.com/nix-community/disko/blob/a08bfe06b39e94eec98dd089a2c1b18af01fef19/example/hybrid-mbr.nix#L21C37-L21C41

@Mic92 Thanks for chiming in so (very!) fast 😉

Would I still need this one in that case (I suppose it's the "container" for the hybrid attribute?) and would it be ok to make it "symbolic" size (say 1M)? I guess the initrd and kernel will be on the separate /boot anyway?

Maybe?

[ppenguin]

@altsalt I did that on my first try, but it appears I have an additional complication on my Microserver Gen8: when not using HW RAID and not using one of the 4 bays for the boot drive (but a separate SSD in the CD ROM bay), I can't boot from that but need the on-board SD card for (at least?) the MBR. So I'll be adding that to the disco config and see what happens...

EDIT:
Thanks guys 🤟

That did the trick. Thanks to those tricks (and praise the lord for iLO 🚀 ) I ended up with this config working (me being lazy I just have MBR + boot on the SD card, should be good to reboot a few times per decade on this server 😉 ):

disk-config.nix

{
  disko.devices = {
    disk = {
      main = {
        type = "disk";
        device = "/dev/disk/by-id/ata-TS128GSSD230S_023331F2E08571140568"; # SSD 120G (formerly sdc)
        content = {
          type = "gpt";
          partitions = {
            plainSwap = {
              size = "16G";
              content = {
                type = "swap";
                discardPolicy = "both";
              };
            };
            primary = {
              size = "100%";
              content = {
                type = "lvm_pv";
                vg = "pool";
              };
            };
          };
        };
      };
      sdcard = {
        type = "disk";
        device = "/dev/disk/by-id/usb-HP_iLO_Internal_SD-CARD_000002660A01-0:0"; 
        content = {
          type = "gpt";
          partitions = {
            MBR = {
              size = "1M";
              type = "EF02"; # for grub MBR
            };
            boot = {
              size = "500M";
              type = "EF00";
              content = {
                type = "filesystem";
                format = "vfat";
                mountpoint = "/boot";
                mountOptions = [
                  "defaults"
                ];
              };
            };
          };
        };
      };
    };
    lvm_vg = {
      pool = {
        type = "lvm_vg";
        lvs = {
          root = {
            size = "30G";
            content = {
              type = "filesystem";
              format = "ext4"; 
              mountpoint = "/";
              mountOptions = [
                "defaults"
              ];
            };
          };
          var = {
            size = "100%FREE";
            content = {
              type = "filesystem";
              format = "ext4"; 
              mountpoint = "/var";
              mountOptions = [
                "defaults"
              ];
            };
          };
        };
      };
    };
  };
}