Btrfs: Difference between revisions
m Mount the swap subvolume without tracking access times. |
bees usage |
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<syntaxhighlight lang="console"> | <syntaxhighlight lang="console"> | ||
# nixos-generate-config --root /mnt | # nixos-generate-config --root /mnt | ||
# nano /mnt/etc/nixos/configuration.nix # manually add mount options | # nano /mnt/etc/nixos/configuration.nix # manually add mount options (see Compression below for an example) | ||
# nixos-install | # nixos-install | ||
</syntaxhighlight> | </syntaxhighlight> | ||
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</syntaxhighlight> | </syntaxhighlight> | ||
You can check the status of the ongoing scrubbing process with the same <code>status</code> command from above | You can check the status of the ongoing scrubbing process with the same <code>status</code> command from above | ||
=== Deduplication === | |||
Files with (partially) equal contents can be deduplicated using [https://github.com/Zygo/bees bees] or [https://github.com/markfasheh/duperemove duperemove]. | |||
To use bees, you need to: | |||
# configure the UUID | |||
# mount the filesystem | |||
# create a hash table ([size guidelines](https://github.com/Zygo/bees/blob/master/docs/config.md)) | |||
# run <code>beesd</code> | |||
<syntaxhighlight lang="console"> | |||
# mkdir -p /var/run/bees/configs/bees/ | |||
# echo "UUID=$UUID" > /var/run/bees/configs/bees/root.conf | |||
# mkdir -p /run/bees/mnt/ | |||
# mount /dev/disk/by-uuid/$UUID /run/bees/mnt/$UUID -osubvol=/ | |||
# truncate -s 1g /var/lib/bees/$UUID/.beeshome/beeshash.dat | |||
# chmod 700 /var/lib/bees/$UUID/.beeshome/beeshash.dat | |||
# beesd / | |||
</syntaxhighlight> | |||
== Usage == | == Usage == |
Latest revision as of 12:19, 24 December 2024
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
Partition the disk
# printf "label: gpt\n,550M,U\n,,L\n" | sfdisk /dev/sdX
Format partitions and create subvolumes
# nix-shell -p btrfs-progs
# 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 (see Compression below for an example)
# 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 noatime,subvol=swap /dev/sdXY /swap
Then, create the swap file and adjust its size as desired:
# btrfs filesystem mkswapfile --size 8g --uuid clear /swap/swapfile
Finally, add the swap file to your configuration and nixos-rebuild switch
:
swapDevices = [ { device = "/swap/swapfile"; } ];
Scrubbing
Btrfs filesystem by default keeps checksums for all files, and this allows to check if contents of the file has not changed due to hardware malfunctions and other external effects.
Scrubbing - is the process of checking file consistency (for this it may use checksums and/or duplicated copies of data, from raid for example). Scrubbing may be done "online", meaning you don't need to unmount a subvolume to scrub it.
You can enable automatic scrubbing with
services.btrfs.autoScrub.enable = true;
Automatic scrubbing by default is performed once a month, but you can change that with
services.btrfs.autoScrub.interval = "weekly";
interval
syntax is defined by systemd.timer's Calendar Events
By default, autoscrub will scrub all detected btrfs mount points. However, in case of mounted nested subvolumes (like in example above /nix
and /home
are nested subvolumes under /
), you only need to scrub the top-most one. So an example configuration may look like this:
services.btrfs.autoScrub = {
enable = true;
interval = "monthly";
fileSystems = [ "/" ];
};
The result of periodic auto scrub will be save to system journal, however you can also always check the status of the last scrub with
btrfs scrub status /
You can also start a scrubbing in background manually
btrfs scrub start /
You can check the status of the ongoing scrubbing process with the same status
command from above
Deduplication
Files with (partially) equal contents can be deduplicated using bees or duperemove. To use bees, you need to:
- configure the UUID
- mount the filesystem
- create a hash table ([size guidelines](https://github.com/Zygo/bees/blob/master/docs/config.md))
- run
beesd
# mkdir -p /var/run/bees/configs/bees/
# echo "UUID=$UUID" > /var/run/bees/configs/bees/root.conf
# mkdir -p /run/bees/mnt/
# mount /dev/disk/by-uuid/$UUID /run/bees/mnt/$UUID -osubvol=/
# truncate -s 1g /var/lib/bees/$UUID/.beeshome/beeshash.dat
# chmod 700 /var/lib/bees/$UUID/.beeshome/beeshash.dat
# beesd /
Usage
Subvolume
Create a subvolume
btrfs subvolume create /mnt/nixos
Removing a subvolume
btrfs subvolume delete /mnt/nixos
Snapshots
A snapshot in btrfs is simply a subvolume that shares its data (and metadata) with some other subvolume, using btrfs's COW capabilities.
Because of that, there is no special location for snapshots - you need to decide where you want to store them for yourself. It can be a simple directory inside root subvolume, or a directory inside a dedicated "snapshots" subvolume.
For this example we are going to store snapshots in a simple directory /snapshots
, that has to be created beforehand with sudo mkdir /snapshots
Taking a read-only (-r
) snapshot called home_snapshot_202302
of the subvolume mounted at /home
btrfs subvolume snapshot -r /home /snapshots/home_snapshot_202302
You can also snapshot the root subvolume. But keep in mind, that nested subvolumes are not part of a snapshot. So if you have subvolumes /nix /home
, taking snapshot of /
will not include them.
btrfs subvolume snapshot -r / /snapshots/nixos_snapshot_202302
Make snapshot read-write again
btrfs property set -ts /snapshots/home_snapshot_202302 ro false
However, changing read-only property of a snapshot in-place may causes issues with any future incremental send/receive.
Instead, a read-only snapshot itself (being a simple subvolume) can be snapshoted again as a read-write snapshot like this:
btrfs subvolume snapshot /snapshots/home_snapshot_202302 /snapshots/home_snapshot_202302_rw
Or it can be restored directly to /home
straight away like this:
btrfs subvolume delete /home
btrfs subvolume snapshot /snapshots/home_snapshot_202302 /home
After this you can mount /home
again./
Transfer snapshot
Sending the snapshot /snapshots/nixos_snapshot_202302
compressed to a remote host via ssh at root@192.168.178.110
and saving it to a subvolume mounted or directory at /mnt/nixos
sudo btrfs send /snapshots/nixos_snapshot_202302 | zstd | ssh root@192.168.178.110 'zstd -d | btrfs receive /mnt/nixos'
Installation with encryption
Using Luks2:
cryptsetup --verify-passphrase -v luksFormat "$DISK"p2
cryptsetup open "$DISK"p2 enc
You can use any device paritition for your bootloader # Notice that this bootloader is unencrypted on default:
mkfs.vfat -n BOOT "$DISK"p1
Creating Subvolumes
mkfs.btrfs /dev/mapper/enc # Creating btrfs partition
mount -t btrfs /dev/mapper/enc /mnt
# Create the subvolumes
btrfs subvolume create /mnt/root # The subvolume for /
btrfs subvolume create /mnt/home # The subvolume for /home, which should be backed up
btrfs subvolume create /mnt/nix # The subvolume for /nix, which needs to be persistent but is not worth backing up, as it’s trivial to reconstruct
btrfs subvolume create /mnt/log # The subvolume for /var/log.
Unmount to mount on the subvolumes for the next steps:
umount /mnt
Once the subvolumes has been created, mount them with the options. Example with Zstandard compression with noatime:
mount -o subvol=root,compress=zstd,noatime /dev/mapper/enc /mnt
mkdir /mnt/home
mount -o subvol=home,compress=zstd,noatime /dev/mapper/enc /mnt/home
mkdir /mnt/nix
mount -o subvol=nix,compress=zstd,noatime /dev/mapper/enc /mnt/nix
mkdir -p /mnt/var/log
mount -o subvol=log,compress=zstd,noatime /dev/mapper/enc /mnt/var/log
# do not forget to create and mount the bootloader
mkdir /mnt/boot
mount "$DISK"p1 /mnt/boot
Configure hardware-configuration.nix
# enable btrfs support
boot.supportedFilesystems = [ "btrfs" ];
fileSystems."/var/log" =
{ device = "/dev/disk/by-uuid/X";
fsType = "btrfs";
# enable noatime and zstd to the other subvolumes aswell
options = [ "subvol=log" "compress=zstd" "noatime" ];
# to have a correct log order
neededForBoot = true;
};
Generate Nixconfig:
nixos-generate-config --root /mnt