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[https://zfsonlinux.org/ {{PAGENAME}}] ([[wikipedia:en:{{PAGENAME}}]]) - also known as [https://openzfs.org/ OpenZFS] ([[wikipedia:en:OpenZFS]]) - is modern filesystem which is well supported on [[NixOS]].
[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]].


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.
Besides the ''zfs'' package (''ZFS Filesystem Linux Kernel module'') <ref>https://search.nixos.org/packages?channel=unstable&show=zfs&query=zfs</ref> itself there are many packages in the [[{{PAGENAME}}]] ecosystem available.


[[{{PAGENAME}}]] integrates into NixOS via its [[module]] system.  Examples:
[[{{PAGENAME}}]] integrates into NixOS via the ''boot.zfs''<ref>https://search.nixos.org/options?channel=unstable&query=boot.zfs</ref> and ''service.zfs''<ref>https://search.nixos.org/options?channel=unstable&query=services.zfs</ref> options.
* ''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>


== Limitations ==
== Limitations ==


==== latestCompatibleLinuxPackages of ZFS for boot.kernelPackages ====
==== Latest kernel compatible with ZFS ====


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.
Newer kernels might not be supported by ZFS yet. If you are running a kernel which is not officially supported by zfs, the module will refuse to evaluate and show an error.


==== missing support for SWAP on ZFS ====
You can pin to a newer kernel version explicitly, but note that this version may be dropped by upstream and in nixpkgs prior to zfs supporting the next version. See [[Linux kernel]] for more information.<syntaxhighlight lang="nix">
{
  boot.kernelPackages = pkgs.linuxPackages_latest;
  # OR
  boot.kernelPackages = pkgs.linuxPackages_6_6
}
</syntaxhighlight>


ZFS does not support swapfiles. Hibernation must be either disabled with <code><nowiki>boot.kernelParams = [ "nohibernate" ];</nowiki></code>, or be enabled with a separate, non-ZFS swap partition.
This snippet will configure the latest compatible kernel.
Note that this can over time jump back to old kernel versions because non-lts kernel version
get removed over time and their newer replacements might be not supported by zfs yet.


==== boot.zfs.devNodes in virtual machines ====
<syntaxhighlight lang="nix">
{
  lib,
  pkgs,
  config,
  ...
}:


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.
let
  isUnstable = config.boot.zfs.package == pkgs.zfsUnstable;
  zfsCompatibleKernelPackages = lib.filterAttrs (
    name: kernelPackages:
    (builtins.match "linux_[0-9]+_[0-9]+" name) != null
    && (builtins.tryEval kernelPackages).success
    && (
      (!isUnstable && !kernelPackages.zfs.meta.broken)
      || (isUnstable && !kernelPackages.zfs_unstable.meta.broken)
    )
  ) pkgs.linuxKernel.packages;
  latestKernelPackage = lib.last (
    lib.sort (a: b: (lib.versionOlder a.kernel.version b.kernel.version)) (
      builtins.attrValues zfsCompatibleKernelPackages
    )
  );
in
{
  # Note this might jump back and worth as kernel get added or removed.
  boot.kernelPackages = latestKernelPackage;
}
</syntaxhighlight>
 
==== Partial support for SWAP on ZFS ====
 
ZFS does not support swapfiles. SWAP devices can 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 that pull request is merged, it does not fully mitigate the risk. If you wish to enable hibernation regardless and made sure that not swapfiles on ZFS are used, set <code>boot.zfs.allowHibernation = true</code>.
 
==== Zpool not found ====
 
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.
 
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.


==== declarative mounting of ZFS datasets ====
==== declarative mounting of ZFS datasets ====
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== Guides ==
== Guides ==


; OpenZFS Documentation for installing:
==== '''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.}}


A 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'')]
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:
It is about:
Line 36: Line 81:


It is not about:
It is not about:
* Give understandable, easy to follow and close to the standard installation guide instructions
* integrating ZFS into your existing config
* integrating ZFS into your existing config


If an issue arises for this guide, submit an issue or pull request there.
 
==== '''Simple NixOS ZFS in root 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
* 4G 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 with gdisk:
 
<syntaxhighlight lang="bash">
sudo gdisk /dev/nvme0n1
GPT fdisk (gdisk) version 1.0.10
...
# boot partition
Command (? for help): n
Partition number (1-128, default 1):
First sector (2048-1000215182, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-1000215182, default = 1000215175) or {+-}size{KMGTP}: +1G
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): ef00
Changed type of partition to 'EFI system partition'
 
# Swap partition
Command (? for help): n
Partition number (2-128, default 2):
First sector (2099200-1000215182, default = 2099200) or {+-}size{KMGTP}:
Last sector (2099200-1000215182, default = 1000215175) or {+-}size{KMGTP}: +4G
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): 8200
Changed type of partition to 'Linux swap'
 
# root partition
Command (? for help): n
Partition number (3-128, default 3):
First sector (10487808-1000215182, default = 10487808) or {+-}size{KMGTP}:
Last sector (10487808-1000215182, default = 1000215175) or {+-}size{KMGTP}:
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300):
Changed type of partition to 'Linux filesystem'
 
# write changes
Command (? for help): w
 
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
 
Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/nvme0n1.
The operation has completed successfully.
</syntaxhighlight>
Final partition table
<syntaxhighlight lang=bash>
Number  Start (sector)    End (sector)  Size      Code  Name
  1            2048        2099199  1024.0 MiB  EF00  EFI system partition
  2        2099200        10487807  4.0 GiB    8200  Linux swap
  3        10487808      1000215175  471.9 GiB  8300  Linux filesystem
</syntaxhighlight>
 
'''Let's use variables from now on for simplicity.
Get the device ID in <code>/dev/disk/by-id/</code>, in our case here it is <code>nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O</code>
'''
<syntaxhighlight lang=bash>
BOOT=/dev/disk/by-id/nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O-part1
SWAP=/dev/disk/by-id/nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O-part2
DISK=/dev/disk/by-id/nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O-part3
 
'''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 $DISK
# enter the password to decrypt the pool at boot
Enter new passphrase:
Re-enter new passphrase:
 
# Create datasets
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>
 
'''Format boot partition with fat as filesystem'''
<syntaxhighlight lang="bash">
mkfs.fat -F 32 -n boot $BOOT
</syntaxhighlight>
 
'''Enable swap'''
<syntaxhighlight lang="bash">
mkswap -L swap $SWAP
swapon $SWAP
</syntaxhighlight>
 
'''Installation:'''
# Mount boot
<syntaxhighlight lang="bash">
mkdir -p /mnt/boot
mount $BOOT /mnt/boot
 
# Generate the nixos config
nixos-generate-config --root /mnt
...
writing /mnt/etc/nixos/hardware-configuration.nix...
writing /mnt/etc/nixos/configuration.nix...
For more hardware-specific settings, see https://github.com/NixOS/nixos-hardware.
</syntaxhighlight>
 
Now edit the configuration.nix that was just created in <code>/mnt/etc/nixos/configuration.nix</code> and make sure to have at least the following content in it.
 
<syntaxhighlight lang="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";
...
</syntaxhighlight>
 
Now check the hardware-configuration.nix in <code>/mnt/etc/nixos/hardware-configuration.nix</code> and add whats missing e.g. <code>options = [ "zfsutil" ]</code> for all filesystems except boot and <code>randomEncryption = true;</code> for the swap partition. Also change the generated swap device to the partition we created e.g. <code>/dev/disk/by-id/nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O-part2</code> in this case and <code>/dev/disk/by-id/nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O-part1</code> for boot.
 
<syntaxhighlight lang="nix">
...
  fileSystems."/" = {
    device = "zpool/root";
    fsType = "zfs";
    # the zfsutil option is needed when mounting zfs datasets without "legacy" mountpoints
    options = [ "zfsutil" ];
  };
 
  fileSystems."/nix" = {
    device = "zpool/nix";
    fsType = "zfs";
    options = [ "zfsutil" ];
  };
 
  fileSystems."/var" = {
    device = "zpool/var";
    fsType = "zfs";
    options = [ "zfsutil" ];
  };
 
  fileSystems."/home" = {
    device = "zpool/home";
    fsType = "zfs";
    options = [ "zfsutil" ];
  };
 
  fileSystems."/boot" = {
  device = "/dev/disk/by-id/nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O-part1";
  fsType = "vfat";
  };
 
  swapDevices = [{
    device = "/dev/disk/by-id/nvme-SKHynix_HFS512GDE9X081N_FNB6N634510106K5O-part2";
    randomEncryption = true;
  }];
}
</syntaxhighlight>
 
Now you may install nixos with <code>nixos-install</code>


== Importing on boot ==
== Importing on boot ==
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};
};
</syntaxhighlight>
</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>
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 ==
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     # Add the load-key command to the .profile
     # Add the load-key command to the .profile
     echo "zfs load-key -a; killall zfs" >> /root/.profile
     echo "zfs load-key -a; killall zfs" >> /root/.profile
     };
     '';
   };
   };
};
};
Retrieved from "https://wiki.nixos.org/wiki/ZFS"