Revision as of 00:29, 5 February 2023

btrfs is a modern copy on write (CoW) filesystem for Linux aimed at implementing advanced features while also focusing on fault tolerance, repair and easy administration.

Installation

Note: The following example is for EFI enabled systems. Adjust commands accordingly for a BIOS installation.

Partition the disk

# printf "label: gpt\n,550M,U\n,,L\n" | sfdisk /dev/sdX

Format partitions and create subvolumes

# mkfs.fat -F 32 /dev/sdX1

# mkfs.btrfs /dev/sdX2
# mkdir -p /mnt
# mount /dev/sdX2 /mnt
# btrfs subvolume create /mnt/root
# btrfs subvolume create /mnt/home
# btrfs subvolume create /mnt/nix
# umount /mnt

Mount the partitions and subvolumes

# mount -o compress=zstd,subvol=root /dev/sdX2 /mnt
# mkdir /mnt/{home,nix}
# mount -o compress=zstd,subvol=home /dev/sdX2 /mnt/home
# mount -o compress=zstd,noatime,subvol=nix /dev/sdX2 /mnt/nix

# mkdir /mnt/boot
# mount /dev/sdX1 /mnt/boot

Install NixOS

# nixos-generate-config --root /mnt
# nano /mnt/etc/nixos/configuration.nix # manually add mount options
# nixos-install

Configuration

== Compression ==

nixos-generate-config --show-hardware-config doesn't detect mount options automatically, so to enable compression, you must specify it and other mount options in a persistent configuration:

fileSystems = {
  "/".options = [ "compress=zstd" ];
  "/home".options = [ "compress=zstd" ];
  "/nix".options = [ "compress=zstd" "noatime" ];
  "/swap".options = [ "noatime" ];
};

Swap file

Optionally, create a separate subvolume for the swap file. Be sure to regenerate your hardware-configuration.nix if you choose to do this.

# mkdir -p /mnt
# mount /dev/sdXY /mnt
# btrfs subvolume create /mnt/swap
# umount /mnt
# mkdir /swap
# mount -o subvol=swap /dev/sdXY /swap

Then, create the swap file with copy-on-write and compression disabled:

# truncate -s 0 /swap/swapfile
# chattr +C /swap/swapfile
# btrfs property set /swap/swapfile compression none
# dd if=/dev/zero of=/swap/swapfile bs=1M count=4096
# chmod 0600 /swap/swapfile
# mkswap /swap/swapfile

Finally, add the swap file to your configuration and nixos-rebuild switch:

swapDevices = [ { device = "/swap/swapfile"; } ];

Usage

Snapshots =

Taking a read-only (-r) snapshot called nixos_snapshot_202302 of the subvolume mounted at /

btrfs subvolume snapshot -r / /mnt/@nixos_snapshot_202302

List snapshots for /

sudo btrfs subvolume list /

@@ Line 1: / Line 1: @@
 '''btrfs''' is a modern copy on write (CoW) filesystem for Linux aimed at implementing advanced features while also focusing on fault tolerance, repair and easy administration.
-== Installing NixOS on Btrfs ==
+== Installation ==
 {{note|The following example is for EFI enabled systems. Adjust commands accordingly for a BIOS installation.}}
@@ Line 41: / Line 41: @@
 </syntaxhighlight>
-== Compression ==
+== Configuration ==
+=== Compression == =
 <code>nixos-generate-config --show-hardware-config</code> doesn't detect mount options automatically, so to enable compression, you must specify it and other mount options in a persistent configuration:
@@ Line 54: / Line 56: @@
 </syntaxhighlight>
-== Swap file ==
+=== Swap file ===
 Optionally, create a separate subvolume for the swap file. Be sure to regenerate your <code>hardware-configuration.nix</code> if you choose to do this.
@@ Line 80: / Line 82: @@
 <syntaxhighlight lang="nix">
 swapDevices = [ { device = "/swap/swapfile"; } ];
+</syntaxhighlight>
+== Usage ==
+=== Snapshots ====
+Taking a read-only (<code>-r</code>) snapshot called <code>nixos_snapshot_202302</code> of the subvolume mounted at <code>/</code>
+<syntaxhighlight lang="bash">
+btrfs subvolume snapshot -r / /mnt/@nixos_snapshot_202302
+</syntaxhighlight>
+List snapshots for <code>/</code>
+<syntaxhighlight lang="bash">
+sudo btrfs subvolume list /
 </syntaxhighlight>
 [[Category: Configuration]]