# ZFS

1. [TL;DR](#tldr)
1. [Gotchas](#gotchas)
1. [Further readings](#further-readings)
   1. [Sources](#sources)

## TL;DR

<details>
  <summary>Setup</summary>

  <details style='padding: 0 0 0 1rem'>
    <summary>Debian</summary>

Refer the [Debian Wiki].

> [!important]
> Prefer using `stable`'s _mainline_ kernel and tools.
>
> Debian backports' kernels are released quickly enough to leave the userland incomplete at times.<br/>
> This happens often with ZFS, resulting in broken package issues.

```sh
CODENAME="$(lsb_release -cs)"  # or 'stable'
ARCH="$(uname --kernel-release | sed -E 's|.*-(.*)$|\1|')"  # or 'amd64', 'arm64', …
```

```sh
# Use mainline's kernel and tools
cat <<EOF | tee -a '/etc/apt/sources.list.d/zfs.list'
deb http://deb.debian.org/debian ${CODENAME} main contrib non-free
EOF
cat <<EOF | tee -a '/etc/apt/preferences.d/99zfs'
Package: linux-image-* linux-headers-* libnvpair*linux libuutil*linux libzpool*linux libzfs*linux zfsutils-linux zfs-dkms
Pin: release a=${CODENAME}
Pin-Priority: 995
EOF
apt update
apt install -t "${CODENAME}" "linux-image-${ARCH}" "linux-headers-${ARCH}" 'zfsutils-linux' 'zfs-dkms'
shutdown -r now
```

```sh
# Use backports'
cat <<EOF | tee -a '/etc/apt/sources.list.d/zfs.list'
deb http://deb.debian.org/debian ${CODENAME}-backports main contrib non-free
EOF
cat <<EOF | tee -a '/etc/apt/preferences.d/99zfs'
Package: linux-image-* linux-headers-* libnvpair*linux libuutil*linux libzpool*linux libzfs*linux zfsutils-linux zfs-dkms
Pin: release a=${CODENAME}-backports
Pin-Priority: 995
EOF
apt update
apt install -t "${CODENAME}-backports" "linux-image-${ARCH}" "linux-headers-${ARCH}" 'zfsutils-linux' 'zfs-dkms'
shutdown -r now
```

  </details>

  <details style='padding: 0 0 0 1rem'>
    <summary>Mac OS X</summary>

> [!important]
> On M1 and later devices, this requires system extensions to be enabled in the Startup Security Utility.

```sh
brew install --cask 'openzfs'
```

  </details>

  <details style='padding: 0 0 0 1rem'>
    <summary>Manjaro</summary>

Manjaro prebuilds modules for ZFS in a specific kernel line, which name is postfixed by `-zfs` (e.g. `linux515-zfs` for
for `linux-515`).

```sh
# Install the modules' packages for all installed kernels.
sudo pamac install $(mhwd-kernel --listinstalled | grep '*' | awk -F '* ' '{print $2}' | xargs -I {} echo {}-zfs)
```

  </details>

  <details style='padding: 0 0 1rem 1rem'>
    <summary>Raspberry Pi</summary>

The `zfs-dkms` package cannot handle downloading and installing the Raspberry Pi kernel headers automatically, so they
have to be installed **prior** of the ZFS-related packages:

```sh
sudo apt install --upgrade 'raspberrypi-kernel' 'raspberrypi-kernel-headers'
sudo reboot
sudo apt install 'zfs-dkms' 'zfsutils-linux'
```

To be tested: If the running kernel has no updates, the packages installation might be performed together.

  </details>

</details>

<details>
  <summary>Usage</summary>

  <details style='padding: 0 0 0 1rem'>
    <summary>Pools</summary>

Pool options of interest:

- `ashift=XX`
  - Set XX to `9` for 512B sectors, `12` for 4KB sectors, or `16` for 8KB sectors
    ([reference](http://open-zfs.org/wiki/Performance_tuning#Alignment_Shift_.28ashift.29)).
- `version=28`: enable compatibility with ZFS on Linux.

```sh
# Create pools.
zpool create 'pool_name' 'path/to/device'
zpool create -n 'dry_run_pool_name' 'path/to/device'
zpool create -f 'forcefully_created_pool_name' 'path/to/device'
zpool create -m 'path/to/mount/point' 'pool_name' 'path/to/device'
zpool create 'pool_name' raidz 'path/to/device/1' … 'path/to/device/N'
zpool create 'pool_name' raidz1 'path/to/device/1' … 'path/to/device/N'
zpool create 'pool_name' raidz2 'path/to/device/1' … 'path/to/device/N'

# Create encrypted pools using multiple devices.
zpool create \
  -o 'feature@encryption=enabled' \
  -O 'encryption=on' -O 'keyformat=passphrase' \
  'pool_name' \
  '/dev/sdb' '/dev/sdc' '/dev/sdd'

# List available pools.
zpool list
zpool list -Hp -o 'name,size'

# Show pools configuration and status.
# Also shows the status of running operations on the pool.
zpool status
zpool status -x 'pool_name' 'time_in_seconds'

# Show pools i/o statistics.
zpool iostat
zpool iostat 'pool_name' -n '1'

# Check a pool for errors.
# Verifies the checksum of every block.
# Very cpu and disk intensive.
zpool scrub 'pool_name'

# List all pools available for import.
zpool import

# Import pools.
zpool import -a
zpool import -d
zpool import 'pool_name'
zpool import 'pool_name' -N
zpool import 'encrypted_pool_name' -l

# Export pools.
# Unmounts all filesystems in the pool.
zpool export 'pool_name'
zpool export -f 'pool_name'

# Show the history of all pool's operations.
zpool history 'pool_name'

# Create mirrored pools.
zpool create 'pool_name' mirror 'device1' 'device2' mirror 'device3' 'device4'

# Add cache (L2ARC) devices to pools.
zpool add 'pool_name' cache 'cache_disk'

# Show the current version of a pool.
zpool upgrade -v

# Upgrade pools.
zpool upgrade 'pool_name'
zpool upgrade -a

# Get pools' properties.
zpool get all 'pool_name'

# Set pools' properties.
zpool set 'compression=lz4' 'pool_name'

# Add vdevs to mirrored pools.
zpool attach 'pool_name' 'first_drive_in_existing_mirror' 'new_dev'

# Get info about zpools features.
man zpool-features

# Trim pools.
zpool trim 'pool_name'
zpool set 'autotrim=on' 'pool_name'

# Destroy pools.
zpool destroy 'pool_name'

# Restore destroyed pools.
# The pool must be reimported right after the `destroy` command has been issued, before the data is actually deleted.
zpool import -D
```

  </details>

  <details style='padding: 0 0 1rem 1rem'>
    <summary>Datasets (filesystems)</summary>

Options of interest:

- `atime=off`.
- `compression=on`:
  - Activates data compression with the default algorithm.
  - Pools of version 28 cannot use lz4 -- FIXME: check
- `copies=2`: specifies the number of copies of data stored for the dataset.
- `dedup=on`: enables [data deduplication](http://open-zfs.org/wiki/Performance_tuning#Deduplication), but halves the
  write speed.
- `xattr=sa`.

```sh
# List available datasets (filesystems).
zfs list
zfs list -o 'space'  # shortcut for -o 'name,avail,used,usedsnap,usedds,usedrefreserv,usedchild -t filesystem,volume'
zfs list -Hp -o 'name,used' -S 'used'  # sort by 'used' in descending order

# Create new filesystems.
zfs create 'pool_name/filesystem_name'
zfs create -V '1gb' 'pool_name/filesystem_name'
zfs create -o 'encryption=aes-256-ccm' -o 'keyformat=passphrase' 'pool_name/filesystem_name'
zfs create -o 'encryption=on' -o 'keysource=raw,file:///path/to/raw/key' 'pool_name/filesystem_name'
zfs create -o 'encryption=on' -o 'keylocation=file:///path/to/raw/key' 'pool_name/filesystem_name'

# Load or unload encryption keys.
# Needed before mounting encrypted datasets, unless using `zfs mount -l`.
zfs load-key 'pool_name/filesystem_name'
zfs unload-key 'pool_name/filesystem_name'

# Automatically mount or unmount filesystems.
# See 'zfs get mountpoint pool_name' for a dataset's mountpoint's root path.
zfs mount -alv
zfs unmount 'pool_name/filesystem_name'

# Delete filesystems.
zfs destroy 'pool_name/filesystem_name'
zfs destroy -r 'pool_name'
zfs destroy -fr 'pool_name/filesystem_name'

# List snapshots.
zfs list -t 'snapshot'
zfs list -Hp -t 'snapshot' -S 'creation' -o 'name,creation'

# Recursively list snapshots for a given dataset, outputting only name and
# creation date
zfs list -r -t 'snapshot' -o 'name,creation' 'pool_name/filesystem_name'

# Query a file system or volume configuration (get properties).
zfs get 'all' 'pool_name'
zfs get 'aclmode,aclinherit,acltype,xattr' 'pool_name/filesystem_name'

# Enable or change settings on filesystems.
zfs set 'compression=on' 'pool_name/filesystem_name'
zfs set 'dedup=on' 'pool_name/filesystem_name'
zfs set 'mountpoint=/my/mount/path' 'pool_name/filesystem_name'
zfs set 'mountpoint=legacy' 'pool_name/filesystem_name'
zfs set 'quota=1G' 'pool_name/filesystem_name'
zfs set 'reservation=1G' 'pool_name/filesystem_name'

# Reset properties to default.
zfs inherit 'compression' 'pool_name/filesystem_name'
zfs inherit -r 'acltype' 'pool_name/filesystem_name'

# Create new snapshots.
zfs snapshot 'pool_name/filesystem_name@snapshot_name'

# Rollback to snapshots.
zfs rollback -r 'pool_name/filesystem_name@snapshot_name'
zfs rollback -rf 'pool_name/filesystem_name@snapshot_name'

# Clone snapshots.
zfs clone 'pool_name/filesystem_name@snapshot_name' 'path/to/destination'

# Copy snapshots.
zfs send 'source_pool_name/filesystem_name@snapshot_name' > 'path/to/local/destination'
zfs receive 'destination_pool_name/filesystem_name@snapshot_name' < 'path/to/local/snapshot'
zfs send 'source_pool_name/filesystem_name@snapshot_name' | zfs receive 'destination_pool_name/filesystem_name'
zfs send 'source_pool_name/filesystem_name@snapshot_name' | ssh node02 "zfs receive 'destination_pool_name/filesystem_name'"

# Destroy snapshots and clones.
zfs destroy 'pool_name/filesystem_name@snapshot_name'
zfs destroy 'path/to/clone'

# Get more information about zfs volumes properties.
man zfs
```

  </details>

</details>

<details>
  <summary>Real world use cases</summary>

```sh
# Create pools.
sudo zpool create -f \
  -o 'ashift=12' \
  -o 'feature@allocation_classes=disabled' \
  -o 'feature@async_destroy=enabled' \
  -o 'feature@bookmarks=enabled' \
  -o 'feature@device_removal=enabled' \
  -o 'feature@embedded_data=enabled' \
  -o 'feature@empty_bpobj=enabled' \
  -o 'feature@enabled_txg=enabled' \
  -o 'feature@encryption=disabled' \
  -o 'feature@extensible_dataset=enabled' \
  -o 'feature@hole_birth=enabled' \
  -o 'feature@large_dnode=disabled' \
  -o 'feature@obsolete_counts=enabled' \
  -o 'feature@spacemap_histogram=enabled' \
  -o 'feature@spacemap_v2=enabled' \
  -o 'feature@zpool_checkpoint=enabled' \
  -o 'feature@filesystem_limits=enabled' \
  -o 'feature@multi_vdev_crash_dump=enabled' \
  -o 'feature@lz4_compress=enabled' \
  -o 'feature@project_quota=disabled' \
  -o 'feature@resilver_defer=disabled' \
  -o 'feature@sha512=enabled' \
  -o 'feature@skein=enabled' \
  -o 'feature@userobj_accounting=disabled' \
  -O 'atime=off' \
  -O 'relatime=on' \
  -O 'compression=lz4' \
  -O 'logbias=throughput' \
  -O 'normalization=formD' \
  -O 'xattr=sa' \
  'volume_name' \
  '/dev/sdb'

# Create Linux-compatible pools on Mac OS X.
sudo zpool create -f \
  -o comment='USB-C disk 4T' \
  -o version=28 \
  -O casesensitivity='mixed' \
  -O compression='on' \
  -O com.apple.mimic_hfs='on' \
  -O copies=2 \
  -O logbias='throughput' \
  -O normalization='formD' \
  -O xattr='sa' \
  'volume_name' \
  'disk2'

# Encrypt datasets.
# Requires (re)creating the dataset.
zfs send tank/badMemories | zfs recv -o 'encryption=on' -o 'keyformat=passphrase' backups/badMemories

# Create a dataset in a new pool, adjust its permissions, and unmount the pool.
sudo zpool create \
  -o 'feature@encryption=enabled' \
  -O 'encryption=on' -O 'keyformat=passphrase' \
  'vault' '/dev/sdb'
sudo zfs create 'vault/data'
sudo chown "$USER":'users' '/vault/data'
sudo zpool export 'vault'

# Destroy datasets older than the most recent 4
zfs list -Hp -t 'snapshot' -S 'creation' -o 'name' | sed '1,4d' | xargs -n '1' -t zfs destroy -nv

# Destroy all snapshots older than 31d (pre zfs-2.3)
zfs list -Hp -t 'snapshot' -o 'name,creation' | while read -r SNAPSHOT CREATION; do
  if [[ $CREATION -ge $(date -d "31 days ago" +%s) ]]; then
    echo "'$SNAPSHOT' is recent enough to be kept."
  else
    echo "'$SNAPSHOT' is old and is about to be deleted."
    zfs destroy -nv "$SNAPSHOT"
  fi
done
```

</details>

## Gotchas

- One **cannot shrink** an existing pool.
- One **cannot remove vdevs** after a pool is created.
- More than 9 drives in one RAIDZ pool can cause performance regression.<br/>
  Split drives up into multiple, possibly balanced, pools when reaching the 10 disks mark. E.g. use 2 RAIDZ pools with
  5 drives each instead of a single pool with 10 drives.
- One can **add** hot spares to a RAIDZ1 or RAIDZ2 pool.
- One can replace a drive with a bigger one (but **not a smaller one**) one at a time.
- One can mix MIRROR, RAIDZ1 and RAIDZ2 in a pool.
- Datasets needs the mountpoint to be an **empty** folder to be mounted, unless explicitly mounted with `zfs mount`'s -O
  option.
- The ZFS kernel modules are upgraded **much less frequently** than the kernel (at least on Linux).<br/>
  **Always make sure** one's kernel version and ZFS modules are compatible and upgraded together.

## Further readings

- [OpenZFS docs]
- [Oracle Solaris ZFS Administration Guide]
- [Gentoo Wiki]
- [Archlinux Wiki]
- [Sanoid][jimsalterjrs/sanoid]
- [Zrepl][zrepl/zrepl]
- [Encrypting ZFS File Systems]

### Sources

- [Article on ZFS on Linux]
- [cheat.sh/zfs]
- [Creating fully encrypted ZFS pool]
- [Aaron Toponce's article on ZFS administration]
- [How to Enable ZFS Deduplication]
- [ZFS support + kernel, best approach]

<!--
  Reference
  ═╬═Time══
  -->

<!-- Upstream -->
[Encrypting ZFS File Systems]: https://docs.oracle.com/cd/E23824_01/html/821-1448/gkkih.html
[openzfs docs]: https://openzfs.github.io/openzfs-docs/
[oracle solaris zfs administration guide]: https://docs.oracle.com/cd/E19253-01/819-5461/index.html

<!-- Others -->
[aaron toponce's article on zfs administration]: https://pthree.org/2012/12/04/zfs-administration-part-i-vdevs/
[archlinux wiki]: https://wiki.archlinux.org/title/ZFS
[article on zfs on linux]: https://blog.heckel.io/2017/01/08/zfs-encryption-openzfs-zfs-on-linux
[cheat.sh/zfs]: https://cheat.sh/zfs
[creating fully encrypted zfs pool]: https://timor.site/2021/11/creating-fully-encrypted-zfs-pool/
[debian wiki]: https://wiki.debian.org/ZFS
[gentoo wiki]: https://wiki.gentoo.org/wiki/ZFS
[how to enable zfs deduplication]: https://linuxhint.com/zfs-deduplication/
[jimsalterjrs/sanoid]: https://github.com/jimsalterjrs/sanoid
[zfs support + kernel, best approach]: https://forum.manjaro.org/t/zfs-support-kernel-best-approach/33329/2
[zrepl/zrepl]: https://github.com/zrepl/zrepl