Debian Bullseye Root on ZFS

Overview 

Newer release available 

See Debian Bookworm Root on ZFS for new installs. This guide is no longer receiving most updates. It continues to exist for reference for existing installs that followed it.

Caution 

This HOWTO uses a whole physical disk.
Do not use these instructions for dual-booting.
Backup your data. Any existing data will be lost.

System Requirements 

64-bit Debian GNU/Linux Bullseye Live CD w/ GUI (e.g. gnome iso)
A 64-bit kernel is strongly encouraged.
Installing on a drive which presents 4 KiB logical sectors (a “4Kn” drive) only works with UEFI booting. This not unique to ZFS. GRUB does not and will not work on 4Kn with legacy (BIOS) booting.

Computers that have less than 2 GiB of memory run ZFS slowly. 4 GiB of memory is recommended for normal performance in basic workloads. If you wish to use deduplication, you will need massive amounts of RAM. Enabling deduplication is a permanent change that cannot be easily reverted.

Support 

If you need help, reach out to the community using the Mailing Lists or IRC at #zfsonlinux on Libera Chat. If you have a bug report or feature request related to this HOWTO, please file a new issue and mention @rlaager.

Contributing 

Fork and clone: https://github.com/openzfs/openzfs-docs

Install the tools:

sudo apt install python3-pip

pip3 install -r docs/requirements.txt

# Add ~/.local/bin to your $PATH, e.g. by adding this to ~/.bashrc:
PATH=$HOME/.local/bin:$PATH

Make your changes.

Test:

cd docs
make html
sensible-browser _build/html/index.html

git commit --signoff to a branch, git push, and create a pull request. Mention @rlaager.

Encryption 

This guide supports three different encryption options: unencrypted, ZFS native encryption, and LUKS. With any option, all ZFS features are fully available.

Unencrypted does not encrypt anything, of course. With no encryption happening, this option naturally has the best performance.

ZFS native encryption encrypts the data and most metadata in the root pool. It does not encrypt dataset or snapshot names or properties. The boot pool is not encrypted at all, but it only contains the bootloader, kernel, and initrd. (Unless you put a password in /etc/fstab, the initrd is unlikely to contain sensitive data.) The system cannot boot without the passphrase being entered at the console. Performance is good. As the encryption happens in ZFS, even if multiple disks (mirror or raidz topologies) are used, the data only has to be encrypted once.

LUKS encrypts almost everything. The only unencrypted data is the bootloader, kernel, and initrd. The system cannot boot without the passphrase being entered at the console. Performance is good, but LUKS sits underneath ZFS, so if multiple disks (mirror or raidz topologies) are used, the data has to be encrypted once per disk.

Step 1: Prepare The Install Environment 

Boot the Debian GNU/Linux Live CD. If prompted, login with the username user and password live. Connect your system to the Internet as appropriate (e.g. join your WiFi network). Open a terminal.

Setup and update the repositories:

sudo vi /etc/apt/sources.list

deb http://deb.debian.org/debian bullseye main contrib

sudo apt update

Optional: Install and start the OpenSSH server in the Live CD environment:

If you have a second system, using SSH to access the target system can be convenient:
```
sudo apt install --yes openssh-server

sudo systemctl restart ssh
```
Hint: You can find your IP address with ip addr show scope global | grep inet. Then, from your main machine, connect with ssh user@IP.
Disable automounting:

If the disk has been used before (with partitions at the same offsets), previous filesystems (e.g. the ESP) will automount if not disabled:
```
gsettings set org.gnome.desktop.media-handling automount false
```
Become root:
```
sudo -i
```

Install ZFS in the Live CD environment:

apt install --yes debootstrap gdisk zfsutils-linux

Step 2: Disk Formatting 

Set a variable with the disk name:
```
DISK=/dev/disk/by-id/scsi-SATA_disk1
```
Always use the long /dev/disk/by-id/* aliases with ZFS. Using the /dev/sd* device nodes directly can cause sporadic import failures, especially on systems that have more than one storage pool.

Hints:
- ls -la /dev/disk/by-id will list the aliases.
- Are you doing this in a virtual machine? If your virtual disk is missing from /dev/disk/by-id, use /dev/vda if you are using KVM with virtio; otherwise, read the troubleshooting section.
- For a mirror or raidz topology, use DISK1, DISK2, etc.
- When choosing a boot pool size, consider how you will use the space. A kernel and initrd may consume around 100M. If you have multiple kernels and take snapshots, you may find yourself low on boot pool space, especially if you need to regenerate your initramfs images, which may be around 85M each. Size your boot pool appropriately for your needs.
If you are re-using a disk, clear it as necessary:

Ensure swap partitions are not in use:
```
swapoff --all
```
If the disk was previously used in an MD array:
```
apt install --yes mdadm

# See if one or more MD arrays are active:
cat /proc/mdstat
# If so, stop them (replace ``md0`` as required):
mdadm --stop /dev/md0

# For an array using the whole disk:
mdadm --zero-superblock --force $DISK
# For an array using a partition:
mdadm --zero-superblock --force ${DISK}-part2
```
If the disk was previously used with zfs:
```
wipefs -a $DISK
```
For flash-based storage, if the disk was previously used, you may wish to do a full-disk discard (TRIM/UNMAP), which can improve performance:
```
blkdiscard -f $DISK
```
Clear the partition table:
```
sgdisk --zap-all $DISK
```
If you get a message about the kernel still using the old partition table, reboot and start over (except that you can skip this step).
Partition your disk(s):

Run this if you need legacy (BIOS) booting:
```
sgdisk -a1 -n1:24K:+1000K -t1:EF02 $DISK
```
Run this for UEFI booting (for use now or in the future):
```
sgdisk     -n2:1M:+512M   -t2:EF00 $DISK
```
Run this for the boot pool:
```
sgdisk     -n3:0:+1G      -t3:BF01 $DISK
```
Choose one of the following options:
- Unencrypted or ZFS native encryption:
```
sgdisk     -n4:0:0        -t4:BF00 $DISK
```
- LUKS:
```
sgdisk     -n4:0:0        -t4:8309 $DISK
```
If you are creating a mirror or raidz topology, repeat the partitioning commands for all the disks which will be part of the pool.
Create the boot pool:
```
zpool create \
    -o ashift=12 \
    -o autotrim=on -d \
    -o cachefile=/etc/zfs/zpool.cache \
    -o feature@async_destroy=enabled \
    -o feature@bookmarks=enabled \
    -o feature@embedded_data=enabled \
    -o feature@empty_bpobj=enabled \
    -o feature@enabled_txg=enabled \
    -o feature@extensible_dataset=enabled \
    -o feature@filesystem_limits=enabled \
    -o feature@hole_birth=enabled \
    -o feature@large_blocks=enabled \
    -o feature@livelist=enabled \
    -o feature@lz4_compress=enabled \
    -o feature@spacemap_histogram=enabled \
    -o feature@zpool_checkpoint=enabled \
    -O devices=off \
    -O acltype=posixacl -O xattr=sa \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/boot -R /mnt \
    bpool ${DISK}-part3
```
You should not need to customize any of the options for the boot pool.

GRUB does not support all of the zpool features. See spa_feature_names in grub-core/fs/zfs/zfs.c. This step creates a separate boot pool for /boot with the features limited to only those that GRUB supports, allowing the root pool to use any/all features. Note that GRUB opens the pool read-only, so all read-only compatible features are “supported” by GRUB.

Hints:
- If you are creating a mirror topology, create the pool using:
```
zpool create \
    ... \
    bpool mirror \
    /dev/disk/by-id/scsi-SATA_disk1-part3 \
    /dev/disk/by-id/scsi-SATA_disk2-part3
```
- For raidz topologies, replace mirror in the above command with raidz, raidz2, or raidz3 and list the partitions from the additional disks.
- The pool name is arbitrary. If changed, the new name must be used consistently. The bpool convention originated in this HOWTO.
Feature Notes:
- The allocation_classes feature should be safe to use. However, unless one is using it (i.e. a special vdev), there is no point to enabling it. It is extremely unlikely that someone would use this feature for a boot pool. If one cares about speeding up the boot pool, it would make more sense to put the whole pool on the faster disk rather than using it as a special vdev.
- The device_rebuild feature should be safe to use (except on raidz, which it is incompatible with), but the boot pool is small, so this does not matter in practice.
- The log_spacemap and spacemap_v2 features have been tested and are safe to use. The boot pool is small, so these do not matter in practice.
- The project_quota feature has been tested and is safe to use. This feature is extremely unlikely to matter for the boot pool.
- The resilver_defer should be safe but the boot pool is small enough that it is unlikely to be necessary.
- As a read-only compatible feature, the userobj_accounting feature should be compatible in theory, but in practice, GRUB can fail with an “invalid dnode type” error. This feature does not matter for /boot anyway.
Create the root pool:

Choose one of the following options:
- Unencrypted:
```
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -O acltype=posixacl -O xattr=sa -O dnodesize=auto \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/ -R /mnt \
    rpool ${DISK}-part4
```
- ZFS native encryption:
```
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -O encryption=on -O keylocation=prompt -O keyformat=passphrase \
    -O acltype=posixacl -O xattr=sa -O dnodesize=auto \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/ -R /mnt \
    rpool ${DISK}-part4
```
- LUKS:
```
apt install --yes cryptsetup

cryptsetup luksFormat -c aes-xts-plain64 -s 512 -h sha256 ${DISK}-part4
cryptsetup luksOpen ${DISK}-part4 luks1
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -O acltype=posixacl -O xattr=sa -O dnodesize=auto \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/ -R /mnt \
    rpool /dev/mapper/luks1
```
Notes:
- The use of ashift=12 is recommended here because many drives today have 4 KiB (or larger) physical sectors, even though they present 512 B logical sectors. Also, a future replacement drive may have 4 KiB physical sectors (in which case ashift=12 is desirable) or 4 KiB logical sectors (in which case ashift=12 is required).
- Setting -O acltype=posixacl enables POSIX ACLs globally. If you do not want this, remove that option, but later add -o acltype=posixacl (note: lowercase “o”) to the zfs create for /var/log, as journald requires ACLs
- Setting xattr=sa vastly improves the performance of extended attributes. Inside ZFS, extended attributes are used to implement POSIX ACLs. Extended attributes can also be used by user-space applications. They are used by some desktop GUI applications. They can be used by Samba to store Windows ACLs and DOS attributes; they are required for a Samba Active Directory domain controller. Note that xattr=sa is Linux-specific. If you move your xattr=sa pool to another OpenZFS implementation besides ZFS-on-Linux, extended attributes will not be readable (though your data will be). If portability of extended attributes is important to you, omit the -O xattr=sa above. Even if you do not want xattr=sa for the whole pool, it is probably fine to use it for /var/log.
- Setting normalization=formD eliminates some corner cases relating to UTF-8 filename normalization. It also implies utf8only=on, which means that only UTF-8 filenames are allowed. If you care to support non-UTF-8 filenames, do not use this option. For a discussion of why requiring UTF-8 filenames may be a bad idea, see The problems with enforced UTF-8 only filenames.
- recordsize is unset (leaving it at the default of 128 KiB). If you want to tune it (e.g. -O recordsize=1M), see these various blog posts.
- Setting relatime=on is a middle ground between classic POSIX atime behavior (with its significant performance impact) and atime=off (which provides the best performance by completely disabling atime updates). Since Linux 2.6.30, relatime has been the default for other filesystems. See RedHat’s documentation for further information.
- Make sure to include the -part4 portion of the drive path. If you forget that, you are specifying the whole disk, which ZFS will then re-partition, and you will lose the bootloader partition(s).
- ZFS native encryption now defaults to aes-256-gcm.
- For LUKS, the key size chosen is 512 bits. However, XTS mode requires two keys, so the LUKS key is split in half. Thus, -s 512 means AES-256.
- Your passphrase will likely be the weakest link. Choose wisely. See section 5 of the cryptsetup FAQ for guidance.
Hints:
- If you are creating a mirror topology, create the pool using:
```
zpool create \
    ... \
    rpool mirror \
    /dev/disk/by-id/scsi-SATA_disk1-part4 \
    /dev/disk/by-id/scsi-SATA_disk2-part4
```
- For raidz topologies, replace mirror in the above command with raidz, raidz2, or raidz3 and list the partitions from the additional disks.
- When using LUKS with mirror or raidz topologies, use /dev/mapper/luks1, /dev/mapper/luks2, etc., which you will have to create using cryptsetup.
- The pool name is arbitrary. If changed, the new name must be used consistently. On systems that can automatically install to ZFS, the root pool is named rpool by default.

Step 3: System Installation 

Create filesystem datasets to act as containers:
```
zfs create -o canmount=off -o mountpoint=none rpool/ROOT
zfs create -o canmount=off -o mountpoint=none bpool/BOOT
```
On Solaris systems, the root filesystem is cloned and the suffix is incremented for major system changes through pkg image-update or beadm. Similar functionality was implemented in Ubuntu with the zsys tool, though its dataset layout is more complicated, and zsys is on life support. Even without such a tool, the rpool/ROOT and bpool/BOOT containers can still be used for manually created clones. That said, this HOWTO assumes a single filesystem for /boot for simplicity.
Create filesystem datasets for the root and boot filesystems:
```
zfs create -o canmount=noauto -o mountpoint=/ rpool/ROOT/debian
zfs mount rpool/ROOT/debian

zfs create -o mountpoint=/boot bpool/BOOT/debian
```
With ZFS, it is not normally necessary to use a mount command (either mount or zfs mount). This situation is an exception because of canmount=noauto.
Create datasets:
```
zfs create                     rpool/home
zfs create -o mountpoint=/root rpool/home/root
chmod 700 /mnt/root
zfs create -o canmount=off     rpool/var
zfs create -o canmount=off     rpool/var/lib
zfs create                     rpool/var/log
zfs create                     rpool/var/spool
```
The datasets below are optional, depending on your preferences and/or software choices.

If you wish to separate these to exclude them from snapshots:
```
zfs create -o com.sun:auto-snapshot=false rpool/var/cache
zfs create -o com.sun:auto-snapshot=false rpool/var/lib/nfs
zfs create -o com.sun:auto-snapshot=false rpool/var/tmp
chmod 1777 /mnt/var/tmp
```
If you use /srv on this system:
```
zfs create rpool/srv
```
If you use /usr/local on this system:
```
zfs create -o canmount=off rpool/usr
zfs create                 rpool/usr/local
```
If this system will have games installed:
```
zfs create rpool/var/games
```
If this system will have a GUI:
```
zfs create rpool/var/lib/AccountsService
zfs create rpool/var/lib/NetworkManager
```
If this system will use Docker (which manages its own datasets & snapshots):
```
zfs create -o com.sun:auto-snapshot=false rpool/var/lib/docker
```
If this system will store local email in /var/mail:
```
zfs create rpool/var/mail
```
If this system will use Snap packages:
```
zfs create rpool/var/snap
```
If you use /var/www on this system:
```
zfs create rpool/var/www
```
A tmpfs is recommended later, but if you want a separate dataset for /tmp:
```
zfs create -o com.sun:auto-snapshot=false  rpool/tmp
chmod 1777 /mnt/tmp
```
The primary goal of this dataset layout is to separate the OS from user data. This allows the root filesystem to be rolled back without rolling back user data.

If you do nothing extra, /tmp will be stored as part of the root filesystem. Alternatively, you can create a separate dataset for /tmp, as shown above. This keeps the /tmp data out of snapshots of your root filesystem. It also allows you to set a quota on rpool/tmp, if you want to limit the maximum space used. Otherwise, you can use a tmpfs (RAM filesystem) later.

Note: If you separate a directory required for booting (e.g. /etc) into its own dataset, you must add it to ZFS_INITRD_ADDITIONAL_DATASETS in /etc/default/zfs. Datasets with canmount=off (like rpool/usr above) do not matter for this.

Mount a tmpfs at /run:

mkdir /mnt/run
mount -t tmpfs tmpfs /mnt/run
mkdir /mnt/run/lock

Install the minimal system:
```
debootstrap bullseye /mnt
```
The debootstrap command leaves the new system in an unconfigured state. An alternative to using debootstrap is to copy the entirety of a working system into the new ZFS root.

Copy in zpool.cache:

mkdir /mnt/etc/zfs
cp /etc/zfs/zpool.cache /mnt/etc/zfs/

Step 4: System Configuration 

Configure the hostname:

Replace HOSTNAME with the desired hostname:

hostname HOSTNAME
hostname > /mnt/etc/hostname
vi /mnt/etc/hosts

Add a line:
127.0.1.1       HOSTNAME
or if the system has a real name in DNS:
127.0.1.1       FQDN HOSTNAME

Hint: Use nano if you find vi confusing.

Configure the network interface:

Find the interface name:
```
ip addr show
```
Adjust NAME below to match your interface name:
```
vi /mnt/etc/network/interfaces.d/NAME
```
```
auto NAME
iface NAME inet dhcp
```
Customize this file if the system is not a DHCP client.

Configure the package sources:

vi /mnt/etc/apt/sources.list

deb http://deb.debian.org/debian bullseye main contrib
deb-src http://deb.debian.org/debian bullseye main contrib

deb http://deb.debian.org/debian-security bullseye-security main contrib
deb-src http://deb.debian.org/debian-security bullseye-security main contrib

deb http://deb.debian.org/debian bullseye-updates main contrib
deb-src http://deb.debian.org/debian bullseye-updates main contrib

Bind the virtual filesystems from the LiveCD environment to the new system and chroot into it:

mount --make-private --rbind /dev  /mnt/dev
mount --make-private --rbind /proc /mnt/proc
mount --make-private --rbind /sys  /mnt/sys
chroot /mnt /usr/bin/env DISK=$DISK bash --login

Note: This is using --rbind, not --bind.

Configure a basic system environment:

ln -s /proc/self/mounts /etc/mtab
apt update

apt install --yes console-setup locales

Even if you prefer a non-English system language, always ensure that en_US.UTF-8 is available:

dpkg-reconfigure locales tzdata keyboard-configuration console-setup

Install ZFS in the chroot environment for the new system:
```
apt install --yes dpkg-dev linux-headers-generic linux-image-generic

apt install --yes zfs-initramfs

echo REMAKE_INITRD=yes > /etc/dkms/zfs.conf
```
Note: Ignore any error messages saying ERROR: Couldn't resolve device and WARNING: Couldn't determine root device. cryptsetup does not support ZFS.
For LUKS installs only, setup /etc/crypttab:
```
apt install --yes cryptsetup cryptsetup-initramfs

echo luks1 /dev/disk/by-uuid/$(blkid -s UUID -o value ${DISK}-part4) \
    none luks,discard,initramfs > /etc/crypttab
```
The use of initramfs is a work-around for cryptsetup does not support ZFS.

Hint: If you are creating a mirror or raidz topology, repeat the /etc/crypttab entries for luks2, etc. adjusting for each disk.
Install an NTP service to synchronize time. This step is specific to Bullseye which does not install the package during bootstrap. Although this step is not necessary for ZFS, it is useful for internet browsing where local clock drift can cause login failures:
```
apt install systemd-timesyncd
timedatectl
```
You should now see “NTP service: active” in the above timedatectl output.
Install GRUB

Choose one of the following options:
- Install GRUB for legacy (BIOS) booting:
```
apt install --yes grub-pc
```
  Select (using the space bar) all of the disks (not partitions) in your pool.
- Install GRUB for UEFI booting:
```
apt install dosfstools

mkdosfs -F 32 -s 1 -n EFI ${DISK}-part2
mkdir /boot/efi
echo /dev/disk/by-uuid/$(blkid -s UUID -o value ${DISK}-part2) \
   /boot/efi vfat defaults 0 0 >> /etc/fstab
mount /boot/efi
apt install --yes grub-efi-amd64 shim-signed
```
  Notes:
  - The -s 1 for mkdosfs is only necessary for drives which present 4 KiB logical sectors (“4Kn” drives) to meet the minimum cluster size (given the partition size of 512 MiB) for FAT32. It also works fine on drives which present 512 B sectors.
  - For a mirror or raidz topology, this step only installs GRUB on the first disk. The other disk(s) will be handled later.
Optional: Remove os-prober:
```
apt purge --yes os-prober
```
This avoids error messages from update-grub. os-prober is only necessary in dual-boot configurations.
Set a root password:
```
passwd
```

Enable importing bpool

This ensures that bpool is always imported, regardless of whether /etc/zfs/zpool.cache exists, whether it is in the cachefile or not, or whether zfs-import-scan.service is enabled.

vi /etc/systemd/system/zfs-import-bpool.service

[Unit]
DefaultDependencies=no
Before=zfs-import-scan.service
Before=zfs-import-cache.service

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/sbin/zpool import -N -o cachefile=none bpool
# Work-around to preserve zpool cache:
ExecStartPre=-/bin/mv /etc/zfs/zpool.cache /etc/zfs/preboot_zpool.cache
ExecStartPost=-/bin/mv /etc/zfs/preboot_zpool.cache /etc/zfs/zpool.cache

[Install]
WantedBy=zfs-import.target

systemctl enable zfs-import-bpool.service

Note: For some disk configurations (NVMe?), this service may fail with an error indicating that the bpool cannot be found. If this happens, add -d DISK-part3 (replace DISK with the correct device path) to the zpool import command.

Optional (but recommended): Mount a tmpfs to /tmp

If you chose to create a /tmp dataset above, skip this step, as they are mutually exclusive choices. Otherwise, you can put /tmp on a tmpfs (RAM filesystem) by enabling the tmp.mount unit.
```
cp /usr/share/systemd/tmp.mount /etc/systemd/system/
systemctl enable tmp.mount
```

Optional: Install SSH:

apt install --yes openssh-server

vi /etc/ssh/sshd_config
# Set: PermitRootLogin yes

Optional: For ZFS native encryption or LUKS, configure Dropbear for remote unlocking:

apt install --yes --no-install-recommends dropbear-initramfs
mkdir -p /etc/dropbear-initramfs

# Optional: Convert OpenSSH server keys for Dropbear
for type in ecdsa ed25519 rsa ; do
    cp /etc/ssh/ssh_host_${type}_key /tmp/openssh.key
    ssh-keygen -p -N "" -m PEM -f /tmp/openssh.key
    dropbearconvert openssh dropbear \
        /tmp/openssh.key \
        /etc/dropbear-initramfs/dropbear_${type}_host_key
done
rm /tmp/openssh.key

# Add user keys in the same format as ~/.ssh/authorized_keys
vi /etc/dropbear-initramfs/authorized_keys

# If using a static IP, set it for the initramfs environment:
vi /etc/initramfs-tools/initramfs.conf
# The syntax is: IP=ADDRESS::GATEWAY:MASK:HOSTNAME:NIC
# For example:
# IP=192.168.1.100::192.168.1.1:255.255.255.0:myhostname:ens3
# HOSTNAME and NIC are optional.

# Rebuild the initramfs (required when changing any of the above):
update-initramfs -u -k all

Notes:

Converting the server keys makes Dropbear use the same keys as OpenSSH, avoiding host key mismatch warnings. Currently, dropbearconvert doesn’t understand the new OpenSSH private key format, so the keys need to be converted to the old PEM format first using ssh-keygen. The downside of using the same keys for both OpenSSH and Dropbear is that the OpenSSH keys are then available on-disk, unencrypted in the initramfs.
Later, to use this functionality, SSH to the system (as root) while it is prompting for the passphrase during the boot process. For ZFS native encryption, run zfsunlock. For LUKS, run cryptroot-unlock.
You can optionally add command="/usr/bin/zfsunlock" or command="/bin/cryptroot-unlock" in front of the authorized_keys line to force the unlock command. This way, the unlock command runs automatically and is all that can be run.

Optional (but kindly requested): Install popcon

The popularity-contest package reports the list of packages install on your system. Showing that ZFS is popular may be helpful in terms of long-term attention from the distro.
```
apt install --yes popularity-contest
```
Choose Yes at the prompt.

Step 5: GRUB Installation 

Verify that the ZFS boot filesystem is recognized:
```
grub-probe /boot
```
Refresh the initrd files:
```
update-initramfs -c -k all
```
Note: Ignore any error messages saying ERROR: Couldn't resolve device and WARNING: Couldn't determine root device. cryptsetup does not support ZFS.

Workaround GRUB’s missing zpool-features support:

vi /etc/default/grub
# Set: GRUB_CMDLINE_LINUX="root=ZFS=rpool/ROOT/debian"

Optional (but highly recommended): Make debugging GRUB easier:
```
vi /etc/default/grub
# Remove quiet from: GRUB_CMDLINE_LINUX_DEFAULT
# Uncomment: GRUB_TERMINAL=console
# Save and quit.
```
Later, once the system has rebooted twice and you are sure everything is working, you can undo these changes, if desired.
Update the boot configuration:
```
update-grub
```
Note: Ignore errors from osprober, if present.
Install the boot loader:
1. For legacy (BIOS) booting, install GRUB to the MBR:
```
grub-install $DISK
```
Note that you are installing GRUB to the whole disk, not a partition.

If you are creating a mirror or raidz topology, repeat the grub-install command for each disk in the pool.
1. For UEFI booting, install GRUB to the ESP:
```
grub-install --target=x86_64-efi --efi-directory=/boot/efi \
    --bootloader-id=debian --recheck --no-floppy
```
  It is not necessary to specify the disk here. If you are creating a mirror or raidz topology, the additional disks will be handled later.
Fix filesystem mount ordering:

We need to activate zfs-mount-generator. This makes systemd aware of the separate mountpoints, which is important for things like /var/log and /var/tmp. In turn, rsyslog.service depends on var-log.mount by way of local-fs.target and services using the PrivateTmp feature of systemd automatically use After=var-tmp.mount.
```
mkdir /etc/zfs/zfs-list.cache
touch /etc/zfs/zfs-list.cache/bpool
touch /etc/zfs/zfs-list.cache/rpool
zed -F &
```
Verify that zed updated the cache by making sure these are not empty:
```
cat /etc/zfs/zfs-list.cache/bpool
cat /etc/zfs/zfs-list.cache/rpool
```
If either is empty, force a cache update and check again:
```
zfs set canmount=on     bpool/BOOT/debian
zfs set canmount=noauto rpool/ROOT/debian
```
If they are still empty, stop zed (as below), start zed (as above) and try again.

Once the files have data, stop zed:
```
fg
Press Ctrl-C.
```
Fix the paths to eliminate /mnt:
```
sed -Ei "s|/mnt/?|/|" /etc/zfs/zfs-list.cache/*
```

Step 6: First Boot 

Optional: Snapshot the initial installation:
```
zfs snapshot bpool/BOOT/debian@install
zfs snapshot rpool/ROOT/debian@install
```
In the future, you will likely want to take snapshots before each upgrade, and remove old snapshots (including this one) at some point to save space.
Exit from the chroot environment back to the LiveCD environment:
```
exit
```

Run these commands in the LiveCD environment to unmount all filesystems:

mount | grep -v zfs | tac | awk '/\/mnt/ {print $3}' | \
    xargs -i{} umount -lf {}
zpool export -a

If this fails for rpool, mounting it on boot will fail and you will need to zpool import -f rpool, then exit in the initramfs prompt.
Reboot:
```
reboot
```
Wait for the newly installed system to boot normally. Login as root.

Create a user account:

Replace YOUR_USERNAME with your desired username:

username=YOUR_USERNAME

zfs create rpool/home/$username
adduser $username

cp -a /etc/skel/. /home/$username
chown -R $username:$username /home/$username
usermod -a -G audio,cdrom,dip,floppy,netdev,plugdev,sudo,video $username

Mirror GRUB

If you installed to multiple disks, install GRUB on the additional disks.
- For legacy (BIOS) booting:
```
dpkg-reconfigure grub-pc
```
  Hit enter until you get to the device selection screen. Select (using the space bar) all of the disks (not partitions) in your pool.
- For UEFI booting:
```
umount /boot/efi
```
  For the second and subsequent disks (increment debian-2 to -3, etc.):
```
dd if=/dev/disk/by-id/scsi-SATA_disk1-part2 \
   of=/dev/disk/by-id/scsi-SATA_disk2-part2
efibootmgr -c -g -d /dev/disk/by-id/scsi-SATA_disk2 \
    -p 2 -L "debian-2" -l '\EFI\debian\grubx64.efi'

mount /boot/efi
```

Step 7: Optional: Configure Swap 

Caution: On systems with extremely high memory pressure, using a zvol for swap can result in lockup, regardless of how much swap is still available. There is a bug report upstream.

Create a volume dataset (zvol) for use as a swap device:
```
zfs create -V 4G -b $(getconf PAGESIZE) -o compression=zle \
    -o logbias=throughput -o sync=always \
    -o primarycache=metadata -o secondarycache=none \
    -o com.sun:auto-snapshot=false rpool/swap
```
You can adjust the size (the 4G part) to your needs.

The compression algorithm is set to zle because it is the cheapest available algorithm. As this guide recommends ashift=12 (4 kiB blocks on disk), the common case of a 4 kiB page size means that no compression algorithm can reduce I/O. The exception is all-zero pages, which are dropped by ZFS; but some form of compression has to be enabled to get this behavior.
Configure the swap device:

Caution: Always use long /dev/zvol aliases in configuration files. Never use a short /dev/zdX device name.
```
mkswap -f /dev/zvol/rpool/swap
echo /dev/zvol/rpool/swap none swap discard 0 0 >> /etc/fstab
echo RESUME=none > /etc/initramfs-tools/conf.d/resume
```
The RESUME=none is necessary to disable resuming from hibernation. This does not work, as the zvol is not present (because the pool has not yet been imported) at the time the resume script runs. If it is not disabled, the boot process hangs for 30 seconds waiting for the swap zvol to appear.
Enable the swap device:
```
swapon -av
```

Step 8: Full Software Installation 

Upgrade the minimal system:
```
apt dist-upgrade --yes
```
Install a regular set of software:
```
tasksel --new-install
```
Note: This will check “Debian desktop environment” and “print server” by default. If you want a server installation, unselect those.
Optional: Disable log compression:

As /var/log is already compressed by ZFS, logrotate’s compression is going to burn CPU and disk I/O for (in most cases) very little gain. Also, if you are making snapshots of /var/log, logrotate’s compression will actually waste space, as the uncompressed data will live on in the snapshot. You can edit the files in /etc/logrotate.d by hand to comment out compress, or use this loop (copy-and-paste highly recommended):
```
for file in /etc/logrotate.d/* ; do
    if grep -Eq "(^|[^#y])compress" "$file" ; then
        sed -i -r "s/(^|[^#y])(compress)/\1#\2/" "$file"
    fi
done
```
Reboot:
```
reboot
```

Step 9: Final Cleanup 

Wait for the system to boot normally. Login using the account you created. Ensure the system (including networking) works normally.

Optional: Delete the snapshots of the initial installation:

sudo zfs destroy bpool/BOOT/debian@install
sudo zfs destroy rpool/ROOT/debian@install

Optional: Disable the root password:
```
sudo usermod -p '*' root
```
Optional (but highly recommended): Disable root SSH logins:

If you installed SSH earlier, revert the temporary change:
```
sudo vi /etc/ssh/sshd_config
# Remove: PermitRootLogin yes

sudo systemctl restart ssh
```
Optional: Re-enable the graphical boot process:

If you prefer the graphical boot process, you can re-enable it now. If you are using LUKS, it makes the prompt look nicer.
```
sudo vi /etc/default/grub
# Add quiet to GRUB_CMDLINE_LINUX_DEFAULT
# Comment out GRUB_TERMINAL=console
# Save and quit.

sudo update-grub
```
Note: Ignore errors from osprober, if present.
Optional: For LUKS installs only, backup the LUKS header:
```
sudo cryptsetup luksHeaderBackup /dev/disk/by-id/scsi-SATA_disk1-part4 \
    --header-backup-file luks1-header.dat
```
Store that backup somewhere safe (e.g. cloud storage). It is protected by your LUKS passphrase, but you may wish to use additional encryption.

Hint: If you created a mirror or raidz topology, repeat this for each LUKS volume (luks2, etc.).

Troubleshooting 

Rescuing using a Live CD 

Go through Step 1: Prepare The Install Environment.

For LUKS, first unlock the disk(s):

apt install --yes cryptsetup

cryptsetup luksOpen /dev/disk/by-id/scsi-SATA_disk1-part4 luks1
# Repeat for additional disks, if this is a mirror or raidz topology.

Mount everything correctly:

zpool export -a
zpool import -N -R /mnt rpool
zpool import -N -R /mnt bpool
zfs load-key -a
zfs mount rpool/ROOT/debian
zfs mount -a

If needed, you can chroot into your installed environment:

mount --make-private --rbind /dev  /mnt/dev
mount --make-private --rbind /proc /mnt/proc
mount --make-private --rbind /sys  /mnt/sys
mount -t tmpfs tmpfs /mnt/run
mkdir /mnt/run/lock
chroot /mnt /bin/bash --login
mount /boot/efi
mount -a

Do whatever you need to do to fix your system.

When done, cleanup:

exit
mount | grep -v zfs | tac | awk '/\/mnt/ {print $3}' | \
    xargs -i{} umount -lf {}
zpool export -a
reboot

Areca 

Systems that require the arcsas blob driver should add it to the /etc/initramfs-tools/modules file and run update-initramfs -c -k all.

Upgrade or downgrade the Areca driver if something like RIP: 0010:[<ffffffff8101b316>] [<ffffffff8101b316>] native_read_tsc+0x6/0x20 appears anywhere in kernel log. ZoL is unstable on systems that emit this error message.

MPT2SAS 

Most problem reports for this tutorial involve mpt2sas hardware that does slow asynchronous drive initialization, like some IBM M1015 or OEM-branded cards that have been flashed to the reference LSI firmware.

The basic problem is that disks on these controllers are not visible to the Linux kernel until after the regular system is started, and ZoL does not hotplug pool members. See https://github.com/zfsonlinux/zfs/issues/330.

Most LSI cards are perfectly compatible with ZoL. If your card has this glitch, try setting ZFS_INITRD_PRE_MOUNTROOT_SLEEP=X in /etc/default/zfs. The system will wait X seconds for all drives to appear before importing the pool.

QEMU/KVM/XEN 

Set a unique serial number on each virtual disk using libvirt or qemu (e.g. -drive if=none,id=disk1,file=disk1.qcow2,serial=1234567890).

To be able to use UEFI in guests (instead of only BIOS booting), run this on the host:

sudo apt install ovmf
sudo vi /etc/libvirt/qemu.conf

Uncomment these lines:

nvram = [
   "/usr/share/OVMF/OVMF_CODE.fd:/usr/share/OVMF/OVMF_VARS.fd",
   "/usr/share/OVMF/OVMF_CODE.secboot.fd:/usr/share/OVMF/OVMF_VARS.fd",
   "/usr/share/AAVMF/AAVMF_CODE.fd:/usr/share/AAVMF/AAVMF_VARS.fd",
   "/usr/share/AAVMF/AAVMF32_CODE.fd:/usr/share/AAVMF/AAVMF32_VARS.fd"
]

sudo systemctl restart libvirtd.service

VMware 

Set disk.EnableUUID = "TRUE" in the vmx file or vsphere configuration. Doing this ensures that /dev/disk aliases are created in the guest.