ZFS mirror ubuntu boot drive

mirror.sh

#!/bin/sh

# Assumptions and requirements
# - All drives will be formatted. These instructions are not suitable for dual-boot
# - No hardware or software RAID is to be used, these would keep ZFS from detecting disk errors and correcting them. In UEFI settings, set controller mode to AHCI, not RAID
# - These instructions are specific to UEFI systems and GPT. If you have an older BIOS/MBR system, please use https://openzfs.github.io/openzfs-docs/Getting%20Started/Ubuntu/Ubuntu%2020.04%20Root%20on%20ZFS.html

# change the these disks variables to your disks paths (check with  lsblk)
DISK1="/dev/nvme0n1"
DISK2="/dev/nvme1n1"

if [ "$(id -u)" -ne 0 ]; then
    echo "Please run this script with sudo:"
    echo "sudo $0 $*"
    exit 1
fi

echo "Installing dependencies"
apt install -y gdisk mdadm grub-efi-amd64

echo "-- Create partitions on second drive"

echo "Change swap partition type"
sgdisk -t2:FD00 $DISK1

echo "Copy partition table from disk 1 to disk 2"
sgdisk -R $DISK2 $DISK1

echo "Change GUID of second disk"
sgdisk -G $DISK2

# this change seems to take a while to propagate :/
sleep 1

echo "-- Mirror boot pool"

echo "Get GUID of partition 3 on disk 2"
DISK1_PART3_GUID=$(sgdisk -i3 $DISK1 |  grep "^Partition unique GUID:" | awk '{print tolower($4)}')
DISK2_PART3_GUID=$(sgdisk -i3 $DISK2 |  grep "^Partition unique GUID:" | awk '{print tolower($4)}')
echo "DISK 1 PART 3 GUID"
echo $DISK1_PART3_GUID
echo "DISK 2 PART 3 GUID"
echo $DISK2_PART3_GUID

if [ -z  $DISK1_PART3_GUID ]; then
    echo "error: failed to get the disk1 part 3 guid"
    exit 1
fi

if [ -z  $DISK2_PART3_GUID ]; then
    echo "error: failed to get the disk2 part 3 guid"
    exit 1
fi

echo "attach partition to bpool"
zpool attach bpool $DISK1_PART3_GUID /dev/disk/by-partuuid/$DISK2_PART3_GUID || exit 1

# TODO: check for failure here by the zpool status not showing the mirror

echo "-- Mirror root pool"

DISK1_PART4_GUID=$(sgdisk -i4 $DISK1 |  grep "^Partition unique GUID:" | awk '{print tolower($4)}')
DISK2_PART4_GUID=$(sgdisk -i4 $DISK2 |  grep "^Partition unique GUID:" | awk '{print tolower($4)}')

if [ -z  $DISK1_PART4_GUID ]; then
    echo "error: failed to get the disk1 part 4 guid"
    exit 1
fi

if [ -z  $DISK2_PART4_GUID ]; then
    echo "error: failed to get the disk2 part 4 guid"
    exit 1
fi

echo "attach partition to rpool"
zpool attach rpool $DISK1_PART4_GUID /dev/disk/by-partuuid/$DISK2_PART4_GUID || exit 1

# TODO: check for failure here by the zpool status not showing the mirror

echo "-- Mirror Swap"

echo "remove existing swap"
swapoff -a || exit 1

echo "remove the swap mount line in /etc/fstab"
sed -i '/swap/d' /etc/fstab

echo "create software mirror drive for swap"
mdadm --create /dev/md0 --metadata=1.2 --level=mirror --raid-devices=2 ${DISK1}p2 ${DISK2}p2 || exit 1

echo "configure mirror drive for swap"
mkswap -f /dev/md0 || exit 1

echo "place mirror swap in fstab"
sh -c "echo UUID=$(sudo blkid -s UUID -o value /dev/md0) none swap discard 0 0 >> /etc/fstab"

# TODO: verify that line is in fstab cat /etc/fstab

echo "use the new swap"
swapon -a || exit 1

echo "-- Move grub menu to ZFS"

# TODO: verify that grub can  see the ZFS boot pool grub-probe /boot

echo "create EFI file system on second disk"
mkdosfs -F 32 -s 1 -n EFI ${DISK2}p1

echo "remove /boot/grub from fstab"
sed -i '/grub/d' /etc/fstab

echo "umount /boot/grub"
umount /boot/grub

# TODO: Verify with df -h, /boot should be mounted on bpool/BOOT/ubuntu_UID, /boot/efi on /dev/sda1 or similar depending on device name of your first disk, and no /boot/grub

echo "remove /boot/grub"
rm -rf /boot/grub

echo "create ZFS datatset for grub"
zfs create -o com.ubuntu.zsys:bootfs=no bpool/grub

echo "refresh initrd files"
update-initramfs -c -k all

echo "disable memory zeroing to address a performance regression of ZFS on linux"
sed -i.bak "s/GRUB_CMDLINE_LINUX_DEFAULT=\"quiet splash\"/GRUB_CMDLINE_LINUX_DEFAULT=\"quiet splash init_on_alloc=0\"/g" /etc/default/grub

echo "update grub"
update-grub

echo "reload daemon"
systemctl daemon-reload

echo "install grub to the esp"
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu --recheck --no-floppy

echo "disable grub-initrd-fallback.service"
systemctl mask grub-initrd-fallback.service

echo "DONE without errors"

dpkg-reconfigure grub-efi-amd64

Ubuntu 2025.04. MATE edition:

Partition 1: BIOS Boot Partition 2: boot pool Partition 3: swap Partition 4: root pool

I'm absolutely baffled. The above 4 partitions where created when I installed Ubuntu MATE 25.04 with ZFS on a 4GB RAM KVM VM. Today I re-installed this on an 8GB RAM KVM VM, and I only have three partitions:

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048            4095   1024.0 KiB  EF02  
   2            4096         3719167   1.8 GiB     8300  
   3         3719168        41940991   18.2 GiB    8300  

where partition 2 is the boot pool and partition 3 the root pool. And there is no swap enabled whatsoever.

I have tested this script on an Ubuntu 24.04 zfs boot drive, created by the Ubuntu installer.
Source drive is /dev/nvme2n1, target drive is /dev/nvme3n1
The script sets up the partitions on the target drive, but then errors out with a

"cannot attach /dev/disk/by-partuuid/cc88bd42-d537-496f-a4af-dbe62b7211ce to ef57d783-a975-42bd-a5cf-25b0dab6a4fd: no such device in pool."

The uuids on both drives are as follows:

Source /dev/nvme2n1p3: UUID="c807808b-4951-41a3-b977-8f44e4454a75" TYPE="swap" PARTUUID="ef57d783-a975-42bd-a5cf-25b0dab6a4fd"
Target /dev/nvme3n1p3: PARTUUID="cc88bd42-d537-496f-a4af-dbe62b7211ce"

The pools on the source drive are by-id, not by-uuid.

The script creates a partition 3 of unknown type on the target drive.
The corresponding partition 3 on the source drive is a swap partition.

I could finish the job by manually attaching the respective partition of the target drive to the corresponding partition of the source drive, resulting in:

  pool: bpool
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
        The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(7) for details.
  scan: resilvered 148M in 00:00:00 with 0 errors on Sun Jul 20 03:07:34 2025
config:

        NAME                                                     STATE     READ WRITE CKSUM
        bpool                                                    ONLINE       0     0     0
          mirror-0                                               ONLINE       0     0     0
            nvme-KIOXIA-EXCERIA_G2_SSD_62DFC06XFM95-part2        ONLINE       0     0     0
            nvme-SOLIDIGM_SSDPFKKW020X7_SSC2N41421160255E-part2  ONLINE       0     0     0

errors: No known data errors

  pool: rpool
 state: ONLINE
  scan: resilvered 107G in 00:02:00 with 0 errors on Sun Jul 20 03:14:59 2025
config:

        NAME                                                 STATE     READ WRITE CKSUM
        rpool                                                ONLINE       0     0     0
          mirror-0                                           ONLINE       0     0     0
            nvme-eui.00000000000000008ce38e0500bc28fa-part4  ONLINE       0     0     0
            nvme-eui.aca32f03150082e52ee4ac0000000001-part4  ONLINE       0     0     0

errors: No known data errors