From 6248fbc29a64f790c60edd91c4bcebf90253cf5d Mon Sep 17 00:00:00 2001
From: Daniel Langbein <daniel@systemli.org>
Date: Sat, 16 Sep 2023 14:03:26 +0200
Subject: [PATCH] btrfs scrub

---
 hosts/yodaTab/configuration.nix  |  7 -------
 hosts/yodaTux/configuration.nix  |  7 -------
 hosts/yodaYoga/configuration.nix |  7 -------
 modules/base.nix                 | 36 +++++++++++++++++++++++++++++---
 4 files changed, 33 insertions(+), 24 deletions(-)

diff --git a/hosts/yodaTab/configuration.nix b/hosts/yodaTab/configuration.nix
index 1e9be72..494d68d 100644
--- a/hosts/yodaTab/configuration.nix
+++ b/hosts/yodaTab/configuration.nix
@@ -49,13 +49,6 @@ in
       #../../modules/docker.nix
     ];
 
-  # BTRFS compression.
-  # `nixos-generate-config` does not detect mount options, so we add them here.
-  # https://nixos.wiki/wiki/Btrfs#Compression
-  fileSystems = {
-    "/".options = [ "compress=zstd" ];
-  };
-
   networking.hostName = "yodaTab";
   services.openssh.ports = [ 22 ];
   boot.initrd.network.ssh.port = 22;
diff --git a/hosts/yodaTux/configuration.nix b/hosts/yodaTux/configuration.nix
index e666ec3..94693b5 100644
--- a/hosts/yodaTux/configuration.nix
+++ b/hosts/yodaTux/configuration.nix
@@ -49,13 +49,6 @@ in
       ../../modules/docker.nix
     ];
 
-  # BTRFS compression.
-  # `nixos-generate-config` does not detect mount options, so we add them here.
-  # https://nixos.wiki/wiki/Btrfs#Compression
-  fileSystems = {
-    "/".options = [ "compress=zstd" ];
-  };
-
   networking.hostName = "yodaTux";
   services.openssh.ports = [ 22 ];
   boot.initrd.network.ssh.port = 22;
diff --git a/hosts/yodaYoga/configuration.nix b/hosts/yodaYoga/configuration.nix
index 9398c43..13da651 100644
--- a/hosts/yodaYoga/configuration.nix
+++ b/hosts/yodaYoga/configuration.nix
@@ -51,13 +51,6 @@ in
       ../../modules/docker.nix
     ];
 
-  # BTRFS compression.
-  # `nixos-generate-config` does not detect mount options, so we add them here.
-  # https://nixos.wiki/wiki/Btrfs#Compression
-  fileSystems = {
-    "/".options = [ "compress=zstd" ];
-  };
-
   networking.hostName = "yodaYoga";
   services.openssh.ports = [ 2224 ];
   boot.initrd.network.ssh.port = 2225;
diff --git a/modules/base.nix b/modules/base.nix
index fd1af4b..386571c 100644
--- a/modules/base.nix
+++ b/modules/base.nix
@@ -65,9 +65,39 @@
   environment.systemPackages = with pkgs; [
   ];
 
-  # Some programs need SUID wrappers, can be configured further or are
-  # started in user sessions.
-  # programs.mtr.enable = true;
+  # BTRFS compression.
+  #
+  # `nixos-generate-config` does not detect mount options, so we add them here.
+  # https://nixos.wiki/wiki/Btrfs#Compression
+  fileSystems = {
+    "/".options = [ "compress=zstd" ];
+  };
+
+  # BTRFS scrub.
+  #
+  # Scrubbing is the process of checking file consistency.
+  # Scrubbing may be done "online", meaning you don't need to unmount a subvolume to scrub it.
+  # https://nixos.wiki/wiki/Btrfs#Scrubbing
+  # Btrfs scrub is "[a]n online filesystem checking tool. Reads all the data and metadata on the filesystem and uses checksums and the duplicate copies from RAID storage to identify and repair any corrupt data."
+  # https://wiki.archlinux.org/title/btrfs#Scrub
+  # The scrub command operates on a whole filesystem, not just individual subvolumes.
+  # https://unix.stackexchange.com/a/724412
+  #
+  # Manually:
+  #   sudo btrfs scrub start /
+  #   sudo btrfs scrub status /
+  #   #=> UUID:             01f67928-9b35-48b2-aaa6-c58ff6c440a8
+  #   #=> Scrub started:    Sat Sep 16 12:54:47 2023
+  #   #=> Status:           finished
+  #   #=> Duration:         0:00:42
+  #   #=> Total to scrub:   64.43GiB
+  #   #=> Rate:             1.53GiB/s
+  #   #=> Error summary:    no errors found
+  services.btrfs.autoScrub = {
+    enable = true;
+    interval = "monthly";
+    fileSystems = [ "/" ];
+  };
 
   nix.settings.auto-optimise-store = true;