Install Ubuntu 24.04 Server on ZFS Root Mirror (RAID-1) via Autoinstall

In my previous post,

I used:

• Ubuntu 24.04 Server autoinstall
• NoCloud datasource over HTTPS
• Nginx + SSI on nocloud.maksonlee.com
• Guided single-disk ZFS layout (layout: { name: zfs, match: { size: largest } })

This time we’re going one step further:

Install Ubuntu 24.04 on ZFS root with a 2-disk mirror (RAID-1) using Autoinstall, where the actual disk names are passed via URL.

Key ideas:

• The hostname still comes from the <HOST> in the URL.
• The two disks also come from the URL (disk1, disk2), e.g. sda/sdb or nvme0n1/nvme1n1.
• Autoinstall runs guided ZFS on disk1, then a small late-commands script:
  • clones the partition table from disk1 → disk2
  • attaches partition 2 as the mirror leg for bpool
  • attaches partition 4 as the mirror leg for rpool
• The script works for both SATA-style names (sda, sdb) and NVMe (nvme0n1, nvme1n1) by automatically choosing 2/4 vs p2/p4.

ZFS in 60 Seconds (Why Bother Mirroring Root?)

Very short version:

• ZFS checksums every block and can self-heal if one side of a mirror is corrupted.
• Snapshots + clones make upgrades much safer: roll back entire OS datasets in seconds.
• Compression (lz4/zstd) often speeds up I/O and saves space.
• Send/receive gives you efficient incremental backups and replication.

With a mirror:

• You can lose one disk and still boot.
• A weekly/monthly scrub can automatically find and repair latent errors.

This post is about wiring that into Autoinstall + NoCloud in a clean, repeatable way.

URL Design: Encode Host + Disk1 + Disk2

We’ll use this URL pattern for the zr1 seed:

https://nocloud.maksonlee.com/zr1/<HOST>/<DISK1>/<DISK2>/

Examples:

• For a VM with two SATA disks:

autoinstall ds="nocloud-net;s=https://nocloud.maksonlee.com/zr1/zfstest/sda/sdb/"

• For a VM with two NVMe disks:

autoinstall ds="nocloud-net;s=https://nocloud.maksonlee.com/zr1/zfstest/nvme0n1/nvme1n1/"

Cloud-init will fetch:

• .../user-data
• .../meta-data

So both must match the same prefix /zr1/<HOST>/<DISK1>/<DISK2>/.

We’ll extract:

• host_id → hostname / instance-id
• disk1, disk2 → become /dev/<disk1> and /dev/<disk2> in the autoinstall script

1. Nginx: NoCloud Routes for zr1

Only the zr1-specific bits are shown here. Existing b/ and z/ seeds from previous posts can stay as they are.

    # zr1 user-data: /zr1/<HOST>/<DISK1>/<DISK2>/user-data
    location ~ ^/zr1/(?<host_id>[A-Za-z0-9._-]+)/(?<disk1>[A-Za-z0-9._-]+)/(?<disk2>[A-Za-z0-9._-]+)/user-data$ {
        default_type text/plain;
        ssi on; ssi_types *;
        try_files /zr1/_user.ssi =404;
        add_header Cache-Control "no-store";
    }

    # zr1 meta-data: same prefix as user-data
    location ~ ^/zr1/(?<host_id>[A-Za-z0-9._-]+)/(?<disk1>[A-Za-z0-9._-]+)/(?<disk2>[A-Za-z0-9._-]+)/meta-data$ {
        default_type text/plain;
        ssi on; ssi_types *;
        try_files /zr1/_meta.ssi =404;
        add_header Cache-Control "no-store";
    }

Directory layout:

2. zr1/_meta.ssi: Instance ID Only

/var/www/html/nocloud/zr1/_meta.ssi:

instance-id: <!--# echo var="host_id" -->

Same pattern as the previous posts: instance-id comes from the <HOST> segment in the URL.

3. zr1/_user.ssi: ZFS Root + Disk1/Disk2 Mirror

This is the core of the post.

We:

• Build a normal autoinstall document (#cloud-config + autoinstall:).
• Use guided ZFS layout (layout: name: zfs) on /dev/<disk1>.
• Use late-commands to:
  • clone the partition table from /dev/<disk1> to /dev/<disk2>
  • attach partition 2 as a mirror for bpool
  • attach partition 4 as a mirror for rpool
• Auto-handle NVMe vs non-NVMe naming (p2 vs 2).

/var/www/html/nocloud/zr1/_user.ssi:

#cloud-config
autoinstall:
  version: 1

  identity:
    hostname: <!--# echo var="host_id" -->
    username: ubuntu
    password: "$6$PWguV961aHQjVEUh$EbowTJLSSunVj2zejKxIlS9A6iRBoG8J8XKnTukaTvtyW5QUzK.XQDFv9nEDyBpSpEOmQGMteP5ucnBBI6YsV0"

  timezone: Asia/Taipei
  locale: en_US.UTF-8
  keyboard:
    layout: us

  ssh:
    install-server: true
    allow-pw: true

  apt:
    primary:
      - arches: [default]
        uri: http://archive.ubuntu.com/ubuntu/

  storage:
    layout:
      name: zfs
      match:
        path: /dev/<!--# echo var="disk1" -->

  user-data:
    preserve_hostname: false
    package_update: true
    packages:
      - htop
    runcmd:
      - [bash, -lc, "lsb_release -a || true"]
      - [bash, -lc, "lsblk -f"]

  late-commands:
    - [curtin, in-target, --target=/target, --, bash, -euxc, 'DISK1=/dev/<!--# echo var="disk1" -->; DISK2=/dev/<!--# echo var="disk2" -->; if [[ "$DISK2" == *nvme* || "$DISK2" == *mmcblk* ]]; then PSEP="p"; else PSEP=""; fi; if ! lsblk -dn "$DISK2" >/dev/null 2>&1; then echo "WARNING: $DISK2 not present, skipping mirror setup"; exit 0; fi; echo "Copying partition table from $DISK1 to $DISK2..."; sgdisk --zap-all "$DISK2"; sgdisk --backup=/tmp/d1.gpt "$DISK1"; sgdisk --load-backup=/tmp/d1.gpt "$DISK2"; sgdisk --randomize-guids "$DISK2"; partprobe "$DISK2"; echo "Attaching ${DISK2}${PSEP}2 to bpool as mirror..."; zpool attach -f bpool "${DISK1}${PSEP}2" "${DISK2}${PSEP}2"; echo "Attaching ${DISK2}${PSEP}4 to rpool as mirror..."; zpool attach -f rpool "${DISK1}${PSEP}4" "${DISK2}${PSEP}4"; zpool status']

What this script is actually doing

Conceptually:

• Let:
  • $DISK1 = /dev/<disk1> (first disk from URL)
  • $DISK2 = /dev/<disk2> (second disk from URL)
• Determine if we need pN suffix (for nvme0n1p2) or N (for sda2):
  • for NVMe/mmc → PSEP="p"
  • for others → PSEP=""
• Then:
  • Clone the partition table from $DISK1 to $DISK2.
  • Attach partition 2 on $DISK2 as mirror leg for bpool.
  • Attach partition 4 on $DISK2 as mirror leg for rpool.

The result is exactly the same as a “hand-crafted ZFS mirror pool”, but you:

• re-use Ubuntu’s guided ZFS layout (correct bpool/rpool/datasets),
• and use a tiny, easy-to-read late-commands block to add mirroring.

4. Find Your Disk Names (One-Time Interactive Boot)

Before you can use the zr1 URL pattern:

https://nocloud.maksonlee.com/zr1/<HOST>/<DISK1>/<DISK2>/

you need to know what the installer sees as <DISK1> and <DISK2>
(sda / sdb, nvme0n1 / nvme1n1, etc).

Do this once per machine type:

• Boot the Ubuntu 24.04 Server ISO normally
  Don’t add autoinstall or ds= yet. Just boot into the regular installer.
• When you’re at the first installer screen (language/keyboard),
  switch to a shell on another TTY:

Ctrl+Alt+F2

• In the shell, list disks:

lsblk -d -o NAME,SIZE,MODEL

Example:

• Decide which two disks you want to mirror as root.
  For example:
  • VM: sda + sdb
  • NVMe box: nvme0n1 + nvme1n1

5. GRUB: Boot the Installer with ds= for zr1

At the Ubuntu 24.04 Server installer GRUB menu:

• Press e on the entry you want to boot.
• Find the linux line.
• Append a ds= parameter with your chosen host and disk names.

Example for SATA disks:

autoinstall ds="nocloud-net;s=https://nocloud.maksonlee.com/zr1/zfstest/sda/sdb/"

Example for NVMe disks:

autoinstall ds="nocloud-net;s=https://nocloud.maksonlee.com/zr1/zfstest/nvme0n1/nvme1n1/"

6. Preflight: Curl the NoCloud Endpoints Before Booting

Double-check your endpoints before you actually autoinstall anything:

# meta-data: should show "instance-id: zfstest"
curl -s https://nocloud.maksonlee.com/zr1/zfstest/sda/sdb/meta-data

# user-data: should render hostname: zfstest and disk1/disk2 correctly
curl -s https://nocloud.maksonlee.com/zr1/zfstest/sda/sdb/user-data

If both look right, you’re safe to boot the installer with that ds= string.

7. Verifying the Result: ZFS Mirror on Root

After the installation completes and you boot into the new system:

• Disks and Partitions

lsblk -o NAME,SIZE,TYPE,MOUNTPOINTS

You should see something like (for 30G test disks):

And both GPTs match:

sudo sgdisk -p /dev/sda
sudo sgdisk -p /dev/sdb

• Confirm Root on ZFS

mount | grep ' on / '

Example:

• Check ZFS Pools are Mirrored

zpool status

Expected:

ZFS calls the vdev mirror-0 — that’s effectively your RAID-1:

• bpool = mirror(sda2, sdb2)
• rpool = mirror(sda4, sdb4)