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== Notes ==
[https://zfsonlinux.org/ {{PAGENAME}}] ([[wikipedia:en:{{PAGENAME}}]]) - also known as [https://openzfs.org/ OpenZFS] ([[wikipedia:en:OpenZFS]]) - is a modern filesystem[[category:filesystem]] which is well supported on [[NixOS]].
* Newest kernels might not be supported by ZFS yet. If you are running an newer kernel which is not yet officially supported by zfs, the zfs module will refuse to evaluate and show up as ''broken''.  Use <code>boot.kernelPackages = config.boot.zfs.package.latestCompatibleLinuxPackages;</code>


* ZFS does not support swap. Hibernation must be either disabled with <code><nowiki>boot.kernelParams = [ "nohibernate" ];</nowiki></code>, or enabled with a separate, non-ZFS swap partition.
There are a lot of packages for [[{{PAGENAME}}]]. For example there is the ''zfs'' package (''ZFS Filesystem Linux Kernel module'') itself.<ref>https://search.nixos.org/packages?channel=unstable&show=zfs&query=zfs</ref> But there are also a lot of packages of the [[{{PAGENAME}}]] ecosystem available.


* By default, all ZFS pools available to the system will be forcibly imported during boot. This behaviour can be disabled by setting <syntaxhighlight lang="nix" inline>boot.zfs.forceImportAll = false;</syntaxhighlight>.
[[{{PAGENAME}}]] integrates into NixOS via its [[module]] system.  Examples:
* ''boot.zfs''<ref>https://search.nixos.org/options?channel=unstable&query=boot.zfs</ref>
* ''service.zfs''<ref>https://search.nixos.org/options?channel=unstable&query=services.zfs</ref>


* If you are running within a VM and NixOS fails to import the zpool on reboot, you may need to add <syntaxhighlight lang="nix" inline>boot.zfs.devNodes = "/dev/disk/by-path";</syntaxhighlight> to your configuration.nix file.
== Limitations ==


== Enable ZFS support ==
==== latestCompatibleLinuxPackages of ZFS for boot.kernelPackages ====


Common ZFS installation guides are now maintained at [https://openzfs.github.io/openzfs-docs/Getting%20Started/NixOS/index.html OpenZFS Documentation] website. Visit there for details and if an issue arises, submit an issue or pull request.
Newest kernels might not be supported by ZFS yet. If you are running an newer kernel which is not yet officially supported by zfs, the zfs module will refuse to evaluate and show up as ''broken''.  Use <code>boot.kernelPackages = config.boot.zfs.package.latestCompatibleLinuxPackages;</code> to use the latest compatible kernel.


== Root on ZFS ==
==== partial support for SWAP on ZFS ====


Root on ZFS guide is now maintained at [https://openzfs.github.io/openzfs-docs/Getting%20Started/NixOS/Root%20on%20ZFS.html OpenZFS Documentation] website. Visit there for details and if an issue arises, submit an issue or pull request.
ZFS does not support swapfiles. SWAP devices must be used instead. Additionally, hibernation is disabled by default due to a [https://github.com/NixOS/nixpkgs/pull/208037 high risk] of data corruption. Note that even if / after that pull request is merged, it does not fully mitigate the risk. If you wish to enable hibernation regardless, set <code>boot.zfs.allowHibernation = true</code>.


== Immutable Root on ZFS ==
==== boot.zfs.devNodes ====


After following the [https://openzfs.github.io/openzfs-docs/Getting%20Started/NixOS/Root%20on%20ZFS.html OpenZFS Documentation], immutable root can be optionally enabled to clean up root filesystem at boot.
If NixOS fails to import the zpool on reboot, you may need to add <syntaxhighlight lang="nix" inline>boot.zfs.devNodes = "/dev/disk/by-path";</syntaxhighlight> or <syntaxhighlight lang="nix" inline>boot.zfs.devNodes = "/dev/disk/by-partuuid";</syntaxhighlight> to your configuration.nix file.


This involves mounting the existing root at a different location and bind mount necessary configuration files from the new mount point. We will use <code>/altroot</code> here.
The differences can be tested by running <code>zpool import -d /dev/disk/by-id</code> when none of the pools are discovered, eg. a live iso.


<syntaxhighlight lang="nix">
==== declarative mounting of ZFS datasets ====
## In /etc/nixos/configuration.nix:
 
   systemd.services.zfs-mount.enable = false;
When using legacy mountpoints (created with eg<code>zfs create -o mountpoint=legacy</code>) mountpoints must be specified with <code>fileSystems."/mount/point" = {};</code>. ZFS native mountpoints are not managed as part of the system configuration but better support hibernation with a separate swap partition. This can lead to conflicts if ZFS mount service is also enabled for the same datasets. Disable it with <code>systemd.services.zfs-mount.enable = false;</code>.
 
== Guides ==
 
==== '''OpenZFS Documentation for installing''' ====
 
{{warning|This guide is not endorsed by NixOS and some features like immutable root do not have upstream support and could break on updates. If an issue arises while following this guide, please consult the guides support channels.}}
 
One guide for a NixOS installation with ZFS is maintained at [https://openzfs.github.io/openzfs-docs/Getting%20Started/NixOS/ OpenZFS Documentation (''Getting Started'' for ''NixOS'')]
 
It is about:
* [https://openzfs.github.io/openzfs-docs/Getting%20Started/NixOS/index.html#installation enabling ZFS on an existing NixOS installation] and
* [https://openzfs.github.io/openzfs-docs/Getting%20Started/NixOS/#root-on-zfs (installing NixOS with) Root on ZFS].
 
It is not about:
* Give understandable, easy to follow and close to the standard installation guide instructions
* integrating ZFS into your existing config
 
 
==== '''Simple NixOS ZFS installation''' ====
 
Start from here in the NixOS manual: [https://nixos.org/manual/nixos/stable/#sec-installation-manual].
Under manual partitioning [https://nixos.org/manual/nixos/stable/#sec-installation-manual-partitioning] do this instead:
 
'''Partition your disk with your favorite partition tool.'''
 
We need the following partitions:
 
* 1G for boot partition with "boot" as the partition label (also called name in some tools) and ef00 as partition code
* 10G for a swap partition with "swap" as the partition label and 8200 as partition code. We will encrypt this with a random secret on each boot.
* The rest of disk space for zfs with "root" as the partition label and 8300 as partition code (default code)
 
Reason for swap partition: ZFS does use a caching mechanism that is different from the normal Linux cache infrastructure.
In low-memory situations, ZFS therefore might need a bit longer to free up memory from its cache. The swap partition will help with that.
 
Example output from fdisk:
 
<syntaxhighlight lang="bash">
sudo gdisk /dev/nvme0n1
GPT fdisk (gdisk) version 1.0.9.1
...
Command (? for help): p
Disk /dev/nvme0n1: 500118192 sectors, 238.5 GiB
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): CA926E8C-47F6-416A-AD1A-C2190CF5D1F8
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 500118158
Partitions will be aligned on 2048-sector boundaries
Total free space is 2669 sectors (1.3 MiB)
 
Number  Start (sector)    End (sector)  Size      Code  Name
  1            2048        2099199  1024.0 MiB  EF00  boot
  2        2099200        23070719   10.0 GiB    8200  swap
  3        23070720      500117503  227.5 GiB  8300  root
 
Command (? for help):
</syntaxhighlight>
 
'''Make zfs pool with encryption and mount points:'''
 
'''Note:''' zpool config can significantly affect performance (especially the ashift option) so you may want to do some research. The [https://jrs-s.net/2018/08/17/zfs-tuning-cheat-sheet/ ZFS tuning cheatsheet] or [https://wiki.archlinux.org/title/ZFS#Storage_pools ArchWiki] is a good place to start.
<syntaxhighlight lang="bash">
zpool create -O encryption=on -O keyformat=passphrase -O keylocation=prompt -O compression=zstd -O mountpoint=none -O xattr=sa -O acltype=posixacl -o ashift=12 zpool /dev/nvme0n1p2
 
zfs create zpool/root
zfs create zpool/nix
zfs create zpool/var
zfs create zpool/home
 
mkdir -p /mnt
mount -t zfs zpool/root /mnt -o zfsutil
mkdir /mnt/nix /mnt/var /mnt/home
 
mount -t zfs zpool/nix /mnt/nix -o zfsutil
mount -t zfs zpool/var /mnt/var -o zfsutil
mount -t zfs zpool/home /mnt/home -o zfsutil
</syntaxhighlight>
 
Output from <syntaxhighlight lang="bash" inline>zpool status</syntaxhighlight>:
<syntaxhighlight >
zpool status
  pool: zpool
state: ONLINE
...
config:
 
NAME                              STATE    READ WRITE CKSUM
zpool                              ONLINE      0    0    0
  nvme-eui.0025384b21406566-part2  ONLINE      0    0    0
 
</syntaxhighlight>
 
'''Make fat filesystem on boot partition'''
<syntaxhighlight lang="bash">
mkfs.fat -F 32 -n boot /dev/nvme0n1p1
</syntaxhighlight>
 
 
'''Installation:'''
 
Install: [https://nixos.org/manual/nixos/stable/#sec-installation-manual-installing]
 
Jump to "2. UEFI systems"


boot.initrd.postDeviceCommands = ''
<syntaxhighlight lang="bash">
  zpool import -Nf rpool
mkdir -p /mnt/boot
  zfs rollback -r rpool/nixos/empty@start
mount /dev/disk/by-partlabel/boot /mnt/boot
  zpool export -a
'';
</syntaxhighlight>
</syntaxhighlight>
Jump to "4." ... /mnt/etc/nixos/configuration.nix ...
Continue from here and add this boot loader and filesystems config to your configuration.nix:


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
## In /etc/nixos/hardware-configuration.nix:
{
  # Boot loader config for configuration.nix:
  boot.loader.systemd-boot.enable = true;
 
  # for local disks that are not shared over the network, we don't need this to be random
  networking.hostId = "8425e349";


## Create new root datasets
  fileSystems."/" = {
# zfs create -o canmount=noauto -o mountpoint=/ rpool/nixos/empty
    device = "zpool/root";
# zfs snapshot rpool/nixos/empty@start
    fsType = "zfs";
    # the zfsutil option is needed when mounting zfs datasets without "legacy" mountpoints
    options = [ "zfsutil" ];
  };


## Replace existing entry for / (root) with
   fileSystems."/nix" = {
   fileSystems."/" =
     device = "zpool/nix";
     { device = "rpool/nixos/empty";
    fsType = "zfs";
      fsType = "zfs"; options = [ "zfsutil" "noatime" "X-mount.mkdir" ];
    options = [ "zfsutil" ];
    };
  };


## Mount old root at /altroot
   fileSystems."/var" = {
## noatime option is used for better performance
     device = "zpool/var";
   fileSystems."/altroot" =
    fsType = "zfs";
     { device = "rpool/nixos/root";
    options = [ "zfsutil" ];
      fsType = "zfs"; options = [ "zfsutil" "noatime" "X-mount.mkdir" ];
  };
      neededForBoot = true;
    };


## /nix/ is needed for the system to boot, so
   fileSystems."/home" = {
## bind mount it from old root
     device = "zpool/home";
   fileSystems."/nix" = {
     fsType = "zfs";
     device = "/altroot/nix";
     options = [ "zfsutil" ];
     fsType = "none";
     options = [ "bind" "X-mount.mkdir" ];
   };
   };


## /etc/nixos/ stores system configuration
   fileSystems."/boot" = {  
   fileSystems."/etc/nixos" = {
  device = "/dev/disk/by-partlabel/boot";
    device = "/altroot/etc/nixos";
  fsType = "vfat";
    fsType = "none";
    options = [ "bind" "X-mount.mkdir" ];
   };
   };
  swapDevices = [{
    device = "/dev/disk/by-partlabel/swap";
    randomEncryption = true;
  }];
}
</syntaxhighlight>
== Importing on boot ==
If you create a zpool, it will not be imported on the next boot unless you either add the zpool name to <syntaxhighlight lang="nix" inline>boot.zfs.extraPools</syntaxhighlight>:
<syntaxhighlight lang="nix">
## In /etc/nixos/configuration.nix:
boot.zfs.extraPools = [ "zpool_name" ];
</syntaxhighlight>
or if you are using legacy mountpoints, add a <syntaxhighlight lang="nix" inline>fileSystems</syntaxhighlight> entry and NixOS will automatically detect that the pool needs to be imported:
<syntaxhighlight lang="nix">
## In /etc/nixos/configuration.nix:
fileSystems."/mount/point" = {
  device = "zpool_name";
  fsType = "zfs";
};
</syntaxhighlight>
=== Zpool created with bus-based disk names ===
If you used bus-based disk names in the <syntaxhighlight inline>zpool create</syntaxhighlight> command, e.g., <syntaxhighlight inline>/dev/sda</syntaxhighlight>, NixOS may run into issues importing the pool if the names change. Even if the pool is able to be mounted (with <syntaxhighlight lang="nix" inline>boot.zfs.devNodes = "/dev/disk/by-partuuid";</syntaxhighlight> set), this may manifest as a <syntaxhighlight inline>FAULTED</syntaxhighlight> disk and a <syntaxhighlight inline>DEGRADED</syntaxhighlight> pool reported by <syntaxhighlight inline>zpool status</syntaxhighlight>. The fix is to re-import the pool using disk IDs:
<syntaxhighlight>
# zpool export zpool_name
# zpool import -d /dev/disk/by-id zpool_name
</syntaxhighlight>
</syntaxhighlight>
The import setting is reflected in <syntaxhighlight inline="" lang="bash">/etc/zfs/zpool.cache</syntaxhighlight>, so it should persist through subsequent boots.
=== Zpool created with disk IDs ===
If you used disk IDs to refer to disks in the <code>zpool create</code> command, e.g., <code>/dev/disk/by-id</code>, then NixOS may consistently fail to import the pool unless <code>boot.zfs.devNodes = "/dev/disk/by-id"</code> is also set.


== Mount datasets at boot ==
== Mount datasets at boot ==
Line 81: Line 227:
boot.kernelParams = [ "zfs.zfs_arc_max=12884901888" ];
boot.kernelParams = [ "zfs.zfs_arc_max=12884901888" ];
</syntaxhighlight>
</syntaxhighlight>
== Tuning other parameters ==
To tune other attributes of ARC, L2ARC or of ZFS itself via runtime modprobe config, add this to your NixOS configuration (keys and values are examples only!):
<syntaxhighlight lang="nix">
    boot.extraModprobeConfig = ''
      options zfs l2arc_noprefetch=0 l2arc_write_boost=33554432 l2arc_write_max=16777216 zfs_arc_max=2147483648
    '';
</syntaxhighlight>
You can confirm whether any specified configuration/tuning got applied via commands like <code>arc_summary</code> and <code>arcstat -a -s " "</code>.


== Automatic scrubbing ==
== Automatic scrubbing ==
Line 91: Line 248:
You can tweak the interval (defaults to once a week) and which pools should be scrubbed (defaults to all).
You can tweak the interval (defaults to once a week) and which pools should be scrubbed (defaults to all).


== Reservations ==
On ZFS, the performance will deteriorate significantly when more than 80% of the available space is used.  To avoid this, reserve disk space beforehand.
To reserve space create a new unused dataset that gets a guaranteed disk space of 10GB.
<syntaxhighlight lang="console">
# zfs create -o refreservation=10G -o mountpoint=none zroot/reserved
</syntaxhighlight>
== Auto ZFS trimming ==
<syntaxhighlight lang="nix" inline>services.zfs.trim.enable = true;</syntaxhighlight>.
For further information read the man pages.
== Take snapshots automatically ==
See <code>services.sanoid</code> section in <code>man configuration.nix</code>.


== Remote unlock ==
== Remote unlock ==
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       authorizedKeys = [ "ssh-rsa AAAA..." ];
       authorizedKeys = [ "ssh-rsa AAAA..." ];
     };
     };
    # this will automatically load the zfs password prompt on login
    # and kill the other prompt so boot can continue
    postCommands = ''
      cat <<EOF > /root/.profile
      if pgrep -x "zfs" > /dev/null
      then
        zfs load-key -a
        killall zfs
      else
        echo "zfs not running -- maybe the pool is taking some time to load for some unforseen reason."
      fi
      EOF
    '';
   };
   };
};
};
</syntaxhighlight>
</syntaxhighlight>
* In order to use DHCP in the initrd, network manager must not be enabled and <syntaxhighlight lang="nix" inline>networking.useDHCP = true;</syntaxhighlight> must be set.
* In order to use DHCP in the initrd, network manager must not be enabled and <syntaxhighlight lang="nix" inline>networking.useDHCP = true;</syntaxhighlight> must be set.
* If your network card isn't started, you'll need to add the according kernel module to the initrd as well, e.g. <syntaxhighlight lang="nix" inline>boot.initrd.kernelModules = [ "r8169" ];</syntaxhighlight>
* If your network card isn't started, you'll need to add the according kernel module to the kernel and initrd as well, e.g. <syntaxhighlight lang="nix">
boot.kernelModules = [ "r8169" ];
boot.initrd.kernelModules = [ "r8169" ];</syntaxhighlight>


=== Import and unlock multiple encrypted pools/dataset at boot ===
After that you can unlock your datasets using the following ssh command:
If you have not only one encrypted pool/dataset but multiple ones and you want to import and unlock them at boot, so that they can be automounted using the hardware-configuration.nix, you could just amend the <code>boot.initrd.network.postCommands</code> option.


Unfortunately having an unlock key file stored in an encrypted zfs dataset cannot be used directly, so the pool must use <code>keyformat=passphrase</code> and <code>keylocation=prompt</code>.
<syntaxhighlight>
ssh -p 2222 root@host "zpool import -a; zfs load-key -a && killall zfs"
</syntaxhighlight>


The following example follows the remote unlocking with OpenSSH, but imports another pool also and prompts for unlocking (either when at the machine itself or when logging in remotely:
Alternatively you could also add the commands as postCommands to your configuration.nix, then you just have to ssh into the initrd:


<syntaxhighlight lang="nix">
<syntaxhighlight>
boot = {
boot = {
   initrd.network = {
   initrd.network = {
    enable = true;
    ssh = {
      enable = true;
      port = 2222;
      hostKeys = [ /path/to/ssh_host_rsa_key ];
      authorizedKeys = [ "ssh-rsa AAAA..." ];
    };
     postCommands = ''
     postCommands = ''
      zpool import tankXXX
    # Import all pools
      echo "zfs load-key -a; killall zfs" >> /root/.profile
    zpool import -a
    # Or import selected pools
    zpool import pool2
    zpool import pool3
    zpool import pool4
    # Add the load-key command to the .profile
    echo "zfs load-key -a; killall zfs" >> /root/.profile
     '';
     '';
   };
   };
Line 184: Line 311:
</syntaxhighlight>
</syntaxhighlight>


When you login by SSH into the box or when you have physical access to the machine itself, you will be prompted to supply the unlocking password for your zroot and tankXXX pools.
After that you can unlock your datasets using the following ssh command:
 
<syntaxhighlight>
ssh -p 2222 root@host
</syntaxhighlight>
 
== Reservations ==
 
On ZFS, the performance will deteriorate significantly when more than 80% of the available space is used.  To avoid this, reserve disk space beforehand.
 
To reserve space create a new unused dataset that gets a guaranteed disk space of 10GB.
 
<syntaxhighlight lang="console">
# zfs create -o refreservation=10G -o mountpoint=none zroot/reserved
</syntaxhighlight>
 
== Auto ZFS trimming ==
 
<syntaxhighlight lang="nix" inline>services.zfs.trim.enable = true;</syntaxhighlight>.
 
This will periodically run <code>zpool trim</code>. Note that this is different from the <code>autotrim</code> pool property. For further information, see the <code>zpool-trim</code> and <code>zpoolprops</code> man pages.
 
== Take snapshots automatically ==
 
See <code>services.sanoid</code> section in <code>man configuration.nix</code>.


== NFS share ==
== NFS share ==
With <code>sharenfs</code> property, ZFS has build-in support for generating <code>/etc/exports.d/zfs.exports</code> file, which in turn is processed by NFS service automatically.
With <code>sharenfs</code> property, ZFS has build-in support for generating <code>/etc/exports.d/zfs.exports</code> file, which in turn is processed by NFS service automatically.


Line 205: Line 357:
For more options, see <code>man 5 exports</code>.
For more options, see <code>man 5 exports</code>.


Todo: smbshare property for Samba.
Todo: sharesmb property for Samba.


== Mail notification for ZFS Event Daemon ==
== Mail notification for ZFS Event Daemon ==
Sandro
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