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Bcachefs: Difference between revisions

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[https://bcachefs.org Bcachefs] is a next-generation CoW filesystem that aims to provide features from [[Btrfs]] and [[ZFS]] with a cleaner codebase, more stability, greater speed and a GPL-compatible license. It is built upon Bcache and is mainly developed by Kent Overstreet.  
[https://bcachefs.org Bcachefs] is a next-generation CoW filesystem that aims to provide features from [[Btrfs]] and [[ZFS]] with a cleaner codebase<ref name=":0">citation needed</ref>, more stability<ref name=":0" />, greater speed<ref name=":0" /> and a GPL-compatible license. It is built upon Bcache and is mainly developed by Kent Overstreet.  


== Installation ==
== Installation ==
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== Usage ==
== Usage ==


Format and mount a signle device
Format and mount a single device


<syntaxhighlight lang="console">
<syntaxhighlight lang="console">
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# mount -t bcachefs /dev/sda /mnt
# mount -t bcachefs /dev/sda /mnt
</syntaxhighlight>
</syntaxhighlight>
Or, format and mount multiple devices
<syntaxhighlight lang="console">
# bcachefs format /dev/sda:/dev/sdb:/dev/sdc
# mount -t bcachefs /dev/sda:/dev/sdb:/dev/sdc
</syntaxhighlight>
The same works with partitions, which is probably better for future proofing depending on your specific needs
<syntaxhighlight lang="console">
# bcachefs format /dev/sda1:/dev/sdb2:/dev/sdc3
# mount -t bcachefs /dev/sda1:/dev/sdb2:/dev/sdc3
</syntaxhighlight>


Format drive with encryption enabled, unlock and mount it afterwards. Following bcachefs commands will ask for a password:
Format drive with encryption enabled, unlock and mount it afterwards. Following bcachefs commands will ask for a password:
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# bcachefs unlock /dev/sda
# bcachefs unlock /dev/sda
# mount -t bcachefs /dev/sda /mnt
# mount -t bcachefs /dev/sda /mnt
</syntaxhighlight>
Format a drive with compression on by default, foreground and background
(Available Compression options are <code>gzip</code>, <code>lz4</code>, and <code>zstd</code>)
<syntaxhighlight lang="console">
# bcachefs format --compression=lz4 --background_compression=zstd /dev/sda
# mount -t bcachefs /dev/sda
</syntaxhighlight>
Format a multiple devices with storage tiers, so that reads and writes happen on the fastest disks, with data being stored on slower, bigger drives based on usage patterns
<syntaxhighlight lang="console">
# bcachefs format \
    --label=hdd.hdd1 /dev/sdc \
    --label=hdd.hdd2 /dev/sdd \
    --label=hdd.hdd3 /dev/sde \
    --label=ssd.ssd1 /dev/sdf \
    --label=ssd.ssd2 /dev/sdg
    --foreground_target=ssd \
    --promote_target=ssd \
    --background_target=hdd \
# mount -t bcachefs /dev/sdc:/dev/sdd:/dev/sde:/dev/sdf:/dev/sdg
</syntaxhighlight>
For a better mounting experience in the previous example, use the external UUID that was printed.
<syntaxhighlight lang="console">
# bcachefs format \
    --label=hdd.hdd1 /dev/sdc \
    --label=hdd.hdd2 /dev/sdd \
    --label=hdd.hdd3 /dev/sde \
    --label=ssd.ssd1 /dev/sdf \
    --label=ssd.ssd2 /dev/sdg
    --foreground_target=ssd \
    --promote_target=ssd \
    --background_target=hdd \
# mount -t bcachefs UUID=<UUID>
</syntaxhighlight>
</syntaxhighlight>


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# bcachefs subvolume snapshot /mnt /mnt/snap1
# bcachefs subvolume snapshot /mnt /mnt/snap1
</syntaxhighlight>
</syntaxhighlight>
Filesystem check, fix errors and corruptions where a Bcachefs filesystem is on <code>/dev/sda</code>:
<syntaxhighlight lang="console">
# bcachefs fsck /dev/sda
</syntaxhighlight>Change partition encryption password for <code>/dev/sda1</code><syntaxhighlight lang="console">
# bcachefs set-passphrase /dev/sda1
</syntaxhighlight>
== Configuration ==
Every option for the filesystem can be set by editing <code>/sys/fs/bcachefs/<uuid>/options</code>, for example the file <code>background_compression</code> will change the background compression scheme for background compression. These are persisted with the filesystems, so a bcachefs storage device being mounted on a different computer won't need to know what mount options to use to maintain the same compression levels.
Change encryption password for Bcachefs formatted device <code>/dev/sda1</code>
<syntaxhighlight lang="console">
# bcachefs set-passphrase /dev/sda1
</syntaxhighlight>
Enable zstd compression for device <code>/dev/sda1</code> at mount time
{{file|/etc/nixos/hardware-configuration.nix|nix|<nowiki>
fileSystems."/" =
{ device = "/dev/sda1";
  fsType = "bcachefs";
  options = [ "compression=zstd" ];
};
</nowiki>}}


== Tips and tricks ==
== Tips and tricks ==
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=== Generate bcachefs enabled installation media ===
=== Generate bcachefs enabled installation media ===


Use following Nix expression <code>iso.nix</code> to generate a ISO installation image with a bcachefs enabled kernel
Use following Nix [[Flakes|Flake-expression]] to generate a ISO installation image with a bcachefs enabled kernel


<syntaxhighlight lang="nix">
{{file|flake.nix|nix|<nowiki>
# This module defines a small NixOS installation CD. It does not
# contain any graphical stuff.
{ config, pkgs, lib, ... }:
{
{
   imports = [
   description = "Bcachefs enabled installation media";
    # Currently fails to build due to ZFS incompatibility with bcachefs
  inputs.nixos.url = "nixpkgs/nixos-24.11";
    #<nixpkgs/nixos/modules/installer/cd-dvd/installation-cd-minimal.nix>
  outputs = { self, nixos }: {
     <nixpkgs/nixos/modules/installer/cd-dvd/installation-cd-minimal-new-kernel-no-zfs.nix>
     nixosConfigurations = {
  ];
      exampleIso = nixos.lib.nixosSystem {
  boot.supportedFilesystems = [ "bcachefs" ];
        system = "x86_64-linux";
  # kernelPackages already defined in installation-cd-minimal-new-kernel-no-zfs.nix
        modules = [
  boot.kernelPackages = lib.mkOverride 0 pkgs.linuxPackages_testing_bcachefs;
          "${nixos}/nixos/modules/installer/cd-dvd/installation-cd-minimal-new-kernel-no-zfs.nix"
   isoImage.squashfsCompression = "gzip -Xcompression-level 1";
          ({ lib, pkgs, ... }: {
            # Might be required as a workaround for bug
            # https://github.com/NixOS/nixpkgs/issues/32279
            environment.systemPackages = [ pkgs.keyutils ];
            boot.supportedFilesystems = [ "bcachefs" ];
          })
        ];
      };
    };
   };
}
}
</nowiki>}}
The following commands will generate the iso-image which will be available in the directory <code>./result/iso</code>
<syntaxhighlight lang="console">
# nix build .#nixosConfigurations.exampleIso.config.system.build.isoImage
</syntaxhighlight>
=== NixOS installation on bcachefs ===
Using the installation media generated above, continue the installation as usual following the [https://nixos.org/manual/nixos/stable/index.html#ch-installation instructions of the NixOS manual].
For a UEFI installation, the partitioning needs to be adjusted as following
{{note|Be sure on which disk you'll perform these filesystem operations. All existing data on it will be erased.}}
<syntaxhighlight lang="console">
# parted /dev/sda -- mklabel gpt
# parted /dev/sda -- mkpart ESP fat32 1MB 512MB
# parted /dev/sda -- set 1 esp on
# parted /dev/sda -- mkpart primary 512MB 100%
</syntaxhighlight>
Formatting the boot partition <code>/dev/sda1</code> and the root filesystem <code>/dev/sda2</code>
<syntaxhighlight lang="console">
# mkfs.fat -F 32 -n boot /dev/sda1
# mkfs.bcachefs -L nixos /dev/sda2
</syntaxhighlight>
Formatting and unlocking the encrypted partition would look like this
<syntaxhighlight lang="console">
# nix-shell -p keyutils --run 'keyctl link @u @s'
# bcachefs format --encrypted /dev/sda2
# bcachefs unlock /dev/sda2
</syntaxhighlight>
</syntaxhighlight>
Mount filesystems
There are two ways to mount a bcachefs filesystem. First, by device:


<syntaxhighlight lang="console">
<syntaxhighlight lang="console">
# nix-build '<nixpkgs/nixos>' -A config.system.build.isoImage -I nixos-config=iso.nix
# mount /dev/sda2 /mnt
# mkdir /mnt/boot
# mount /dev/disk/by-label/boot /mnt/boot
</syntaxhighlight>
</syntaxhighlight>


For better reliability as with any other filesystem, one should mount the filesystem by UUID, by replacing any drive specifiers with it.
When you formatted, there was an external UUID shown, but if you lost it, you can retrieve it using
<syntaxhighlight lang="console">
# lsblk -o +uuid,fsType | grep bcachefs
</syntaxhighlight>
And using it like <code>UUID=<UUID></code> in place of <code>/dev/sda1:/dev/sdb1</code> or even just <code>/dev/sda</code>.
Note: this is currently broken as per this [https://github.com/NixOS/nixpkgs/issues/317901 github issue]. As a workaround, use `/dev/disk/by-uuid/<UUID>` or `/dev/disk/by-id` instead. This seems to work for single device systems atleast, although atleast at the time of this writing I could not get it to work on my 4+ device raid system.
Continue installation as recommended by the [https://nixos.org/manual/nixos/stable/index.html#ch-installation NixOS manual].
Before <code>nixos-install</code> you'll have to adapt the generated NixOS configuration to also use the latest Linux kernel supporting Bcachefs. Add the following line to the <code>configuration.nix</code> in your installation root (/mnt):
{{file|/mnt/etc/nixos/configuration.nix|nix|<nowiki>
boot.supportedFilesystems = [ "bcachefs" ];
boot.kernelPackages = pkgs.linuxPackages_latest;
</nowiki>}}
=== Remote encrypted disk unlocking ===
See article on [[Remote disk unlocking#Bcachefs unlocking|remote disk unlocking]] for a guide on how to enable SSH decryption of Bcachefs enabled systems.
=== Automatically mount encrypted device on boot ===
Since the Bcachefs mount options do [https://github.com/koverstreet/bcachefs-tools/pull/266 not support supplying a key file yet], we could use the <code>bcachefs</code> command and run it on boot using a [[Systemd]] unit:<syntaxhighlight lang="nix">
systemd.services."bcachefs-mount" = {
  after = [ "local-fs.target" ];
  wantedBy = [ "multi-user.target" ];
  environment = {
    DEVICE_PATH = "/dev/sda1";
    MOUNT_POINT = "/mnt";
  };
  script = ''
    #!${pkgs.runtimeShell} -e
    ${pkgs.keyutils}/bin/keyctl link @u @s
    # Check if the device path exists
    if [ ! -b "$DEVICE_PATH" ]; then
      echo "Error: Device path $DEVICE_PATH does not exist."
      exit 1
    fi
    # Check if the drive is already mounted
    if ${pkgs.util-linux}/bin/mountpoint -q "$MOUNT_POINT"; then
      echo "Drive already mounted at $MOUNT_POINT. Skipping..."
      exit 0
    fi
    # Wait for the device to become available
    while [ ! -b "$DEVICE_PATH" ]; do
      echo "Waiting for $DEVICE_PATH to become available..."
      sleep 5
    done
    # Mount the device
    ${pkgs.bcachefs-tools}/bin/bcachefs mount -f /etc/keyfile_test "$DEVICE_PATH" "$MOUNT_POINT"
  '';
  serviceConfig = {
    Type = "oneshot";
    User = "root";
  };
};
</syntaxhighlight>This example unit mounts the Bcachefs encrypted partition <code>/dev/sda1</code> to the target <code>/mnt</code> by using the key file <code>/etc/keyfile_test</code>.
[[Category:Filesystem]]
[[Category:Filesystem]]
Retrieved from "https://wiki.nixos.org/wiki/Bcachefs"