diff --git a/extras/snapper.nix b/extras/snapper.nix
new file mode 100644
index 0000000..d0127aa
--- /dev/null
+++ b/extras/snapper.nix
@@ -0,0 +1,359 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}: let
+  cfg = config.services.snapper;
+
+  mkValue = v:
+    if lib.isList v
+    then "\"${
+      lib.concatMapStringsSep " " (lib.escape [
+        "\\"
+        " "
+      ])
+      v
+    }\""
+    else if v == true
+    then "yes"
+    else if v == false
+    then "no"
+    else if lib.isString v
+    then "\"${v}\""
+    else builtins.toJSON v;
+
+  mkKeyValue = k: v: "${k}=${mkValue v}";
+
+  # "it's recommended to always specify the filesystem type"  -- man snapper-configs
+  defaultOf = k:
+    if k == "FSTYPE"
+    then null
+    else configOptions.${k}.default or null;
+
+  safeStr =
+    lib.types.strMatching "[^\n\"]*"
+    // {
+      description = "string without line breaks or quotes";
+      descriptionClass = "conjunction";
+    };
+
+  intOrNumberOrRange = lib.types.either lib.types.ints.unsigned (
+    lib.types.strMatching "[[:digit:]]+(\-[[:digit:]]+)?"
+    // {
+      description = "string containing either a number or a range";
+      descriptionClass = "conjunction";
+    }
+  );
+
+  configOptions = {
+    SUBVOLUME = lib.mkOption {
+      type = lib.types.path;
+      description = ''
+        Path of the subvolume or mount point.
+        This path is a subvolume and has to contain a subvolume named
+        .snapshots.
+        See also man:snapper(8) section PERMISSIONS.
+      '';
+    };
+
+    FSTYPE = lib.mkOption {
+      type = lib.types.enum ["btrfs" "bcachefs"];
+      default = "btrfs";
+      description = ''
+        Filesystem type. Only btrfs is stable and tested.
+      '';
+    };
+
+    ALLOW_GROUPS = lib.mkOption {
+      type = lib.types.listOf safeStr;
+      default = [];
+      description = ''
+        List of groups allowed to operate with the config.
+
+        Also see the PERMISSIONS section in man:snapper(8).
+      '';
+    };
+
+    ALLOW_USERS = lib.mkOption {
+      type = lib.types.listOf safeStr;
+      default = [];
+      example = ["alice"];
+      description = ''
+        List of users allowed to operate with the config. "root" is always
+        implicitly included.
+
+        Also see the PERMISSIONS section in man:snapper(8).
+      '';
+    };
+
+    TIMELINE_CLEANUP = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        Defines whether the timeline cleanup algorithm should be run for the config.
+      '';
+    };
+
+    TIMELINE_CREATE = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        Defines whether hourly snapshots should be created.
+      '';
+    };
+
+    TIMELINE_LIMIT_HOURLY = lib.mkOption {
+      type = intOrNumberOrRange;
+      default = 10;
+      description = ''
+        Limits for timeline cleanup.
+      '';
+    };
+
+    TIMELINE_LIMIT_DAILY = lib.mkOption {
+      type = intOrNumberOrRange;
+      default = 10;
+      description = ''
+        Limits for timeline cleanup.
+      '';
+    };
+
+    TIMELINE_LIMIT_WEEKLY = lib.mkOption {
+      type = intOrNumberOrRange;
+      default = 0;
+      description = ''
+        Limits for timeline cleanup.
+      '';
+    };
+
+    TIMELINE_LIMIT_MONTHLY = lib.mkOption {
+      type = intOrNumberOrRange;
+      default = 10;
+      description = ''
+        Limits for timeline cleanup.
+      '';
+    };
+
+    TIMELINE_LIMIT_QUARTERLY = lib.mkOption {
+      type = intOrNumberOrRange;
+      default = 0;
+      description = ''
+        Limits for timeline cleanup.
+      '';
+    };
+
+    TIMELINE_LIMIT_YEARLY = lib.mkOption {
+      type = intOrNumberOrRange;
+      default = 10;
+      description = ''
+        Limits for timeline cleanup.
+      '';
+    };
+  };
+in {
+  options.services.snapper = {
+    snapshotRootOnBoot = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        Whether to snapshot root on boot
+      '';
+    };
+
+    snapshotInterval = lib.mkOption {
+      type = lib.types.str;
+      default = "hourly";
+      description = ''
+        Snapshot interval.
+
+        The format is described in
+        {manpage}`systemd.time(7)`.
+      '';
+    };
+
+    persistentTimer = lib.mkOption {
+      default = false;
+      type = lib.types.bool;
+      example = true;
+      description = ''
+        Set the `Persistent` option for the
+        {manpage}`systemd.timer(5)`
+        which triggers the snapshot immediately if the last trigger
+        was missed (e.g. if the system was powered down).
+      '';
+    };
+
+    cleanupInterval = lib.mkOption {
+      type = lib.types.str;
+      default = "1d";
+      description = ''
+        Cleanup interval.
+
+        The format is described in
+        {manpage}`systemd.time(7)`.
+      '';
+    };
+
+    filters = lib.mkOption {
+      type = lib.types.nullOr lib.types.lines;
+      default = null;
+      description = ''
+        Global display difference filter. See man:snapper(8) for more details.
+      '';
+    };
+
+    configs = lib.mkOption {
+      default = {};
+      example = lib.literalExpression ''
+        {
+          home = {
+            SUBVOLUME = "/home";
+            ALLOW_USERS = [ "alice" ];
+            TIMELINE_CREATE = true;
+            TIMELINE_CLEANUP = true;
+          };
+        }
+      '';
+
+      description = ''
+        Subvolume configuration. Any option mentioned in man:snapper-configs(5)
+        is valid here, even if NixOS doesn't document it.
+      '';
+
+      type = lib.types.attrsOf (
+        lib.types.submodule {
+          freeformType = lib.types.attrsOf (
+            lib.types.oneOf [
+              (lib.types.listOf safeStr)
+              lib.types.bool
+              safeStr
+              lib.types.number
+            ]
+          );
+
+          options = configOptions;
+        }
+      );
+    };
+  };
+
+  config = lib.mkIf (cfg.configs != {}) (
+    let
+      documentation = [
+        "man:snapper(8)"
+        "man:snapper-configs(5)"
+      ];
+    in {
+      environment = {
+        systemPackages = [pkgs.snapper];
+
+        # Note: snapper/config-templates/default is only needed for create-config
+        #       which is not the NixOS way to configure.
+        etc =
+          {
+            "sysconfig/snapper".text = ''
+              SNAPPER_CONFIGS="${lib.concatStringsSep " " (builtins.attrNames cfg.configs)}"
+            '';
+          }
+          // (lib.mapAttrs' (
+              name: subvolume:
+                lib.nameValuePair "snapper/configs/${name}" {
+                  text = lib.generators.toKeyValue {inherit mkKeyValue;} (
+                    lib.filterAttrs (k: v: v != defaultOf k) subvolume
+                  );
+                }
+            )
+            cfg.configs)
+          // (lib.optionalAttrs (cfg.filters != null) {"snapper/filters/default.txt".text = cfg.filters;});
+      };
+
+      services.dbus.packages = [pkgs.snapper];
+
+      systemd.services.snapperd = {
+        description = "DBus interface for snapper";
+        inherit documentation;
+        serviceConfig = {
+          Type = "dbus";
+          BusName = "org.opensuse.Snapper";
+          ExecStart = "${pkgs.snapper}/bin/snapperd";
+          CapabilityBoundingSet = "CAP_DAC_OVERRIDE CAP_FOWNER CAP_CHOWN CAP_FSETID CAP_SETFCAP CAP_SYS_ADMIN CAP_SYS_MODULE CAP_IPC_LOCK CAP_SYS_NICE";
+          LockPersonality = true;
+          NoNewPrivileges = false;
+          PrivateNetwork = true;
+          ProtectHostname = true;
+          RestrictAddressFamilies = "AF_UNIX";
+          RestrictRealtime = true;
+        };
+      };
+
+      systemd.services.snapper-timeline = {
+        description = "Timeline of Snapper Snapshots";
+        inherit documentation;
+        requires = ["local-fs.target"];
+        serviceConfig.ExecStart = "${pkgs.snapper}/lib/snapper/systemd-helper --timeline";
+      };
+
+      systemd.timers.snapper-timeline = {
+        wantedBy = ["timers.target"];
+        timerConfig = {
+          Persistent = cfg.persistentTimer;
+          OnCalendar = cfg.snapshotInterval;
+        };
+      };
+
+      systemd.services.snapper-cleanup = {
+        description = "Cleanup of Snapper Snapshots";
+        inherit documentation;
+        serviceConfig.ExecStart = "${pkgs.snapper}/lib/snapper/systemd-helper --cleanup";
+      };
+
+      systemd.timers.snapper-cleanup = {
+        description = "Cleanup of Snapper Snapshots";
+        inherit documentation;
+        wantedBy = ["timers.target"];
+        requires = ["local-fs.target"];
+        timerConfig.OnBootSec = "10m";
+        timerConfig.OnUnitActiveSec = cfg.cleanupInterval;
+      };
+
+      systemd.services.snapper-boot = lib.mkIf cfg.snapshotRootOnBoot {
+        description = "Take snapper snapshot of root on boot";
+        inherit documentation;
+        serviceConfig.ExecStart = "${pkgs.snapper}/bin/snapper --config root create --cleanup-algorithm number --description boot";
+        serviceConfig.Type = "oneshot";
+        requires = ["local-fs.target"];
+        wantedBy = ["multi-user.target"];
+        unitConfig.ConditionPathExists = "/etc/snapper/configs/root";
+      };
+
+      assertions = lib.concatMap (
+        name: let
+          sub = cfg.configs.${name};
+        in
+          [
+            {
+              assertion = !(sub ? extraConfig);
+              message = ''
+                The option definition `services.snapper.configs.${name}.extraConfig' no longer has any effect; please remove it.
+                The contents of this option should be migrated to attributes on `services.snapper.configs.${name}'.
+              '';
+            }
+          ]
+          ++ map
+          (attr: {
+            assertion = !(lib.hasAttr attr sub);
+            message = ''
+              The option definition `services.snapper.configs.${name}.${attr}' has been renamed to `services.snapper.configs.${name}.${lib.toUpper attr}'.
+            '';
+          })
+          [
+            "fstype"
+            "subvolume"
+          ]
+      ) (lib.attrNames cfg.configs);
+    }
+  );
+
+  meta.maintainers = with lib.maintainers; [Djabx];
+}
diff --git a/users/tao.nix b/users/tao.nix
index 4957479..9450549 100644
--- a/users/tao.nix
+++ b/users/tao.nix
@@ -91,8 +91,8 @@
     user = "tao";
     dataDir = "/home/tao/sync";
     configDir = "/home/tao/.config/syncthing";
-    overrideDevices = false;
-    overrideFolders = false;
+    overrideDevices = true;
+    overrideFolders = true;
     openDefaultPorts = true;
     settings = {
       devices = {
@@ -129,17 +129,30 @@
           path = "/home/tao/sync";
           devices = devs;
         };
-        "work" = {
-          path = "/home/tao/work";
-          devices = devs;
-        };
+        # "work" = {
+        #   path = "/home/tao/work";
+        #   devices = devs;
+        # };
       };
     };
   };
 
+  # nixpkgs.overlays = [
+  #   (final: prev: {
+  #     options.services.snapper.configs = prev.options.services.snapper.configs.overrideAttrs (old: {
+  #       configOptions.FSTYPE = lib.mkOption {
+  #         type = lib.types.enum ["btrfs" "bcachefs"];
+  #       };
+  #     });
+  #   })
+  # ];
+
+  disabledModules = ["services/misc/snapper.nix"];
+  imports = [../extras/snapper.nix];
   services.snapper.configs = {
     home = {
       SUBVOLUME = "/home";
+      FSTYPE = "bcachefs";
       ALLOW_USERS = ["tao"];
       TIMELINE_CREATE = true;
       TIMELINE_CLEANUP = true;
diff --git a/users/vy.nix b/users/vy.nix
index 7b5c480..7b2b718 100644
--- a/users/vy.nix
+++ b/users/vy.nix
@@ -25,8 +25,8 @@
       ALLOW_USERS = ["vy"];
       TIMELINE_CREATE = true;
       TIMELINE_CLEANUP = true;
-      TIMELINE_LIMIT_HOURLY = "5";
-      TIMELINE_LIMIT_DAILY = "7";
+      TIMELINE_LIMIT_HOURLY = 5;
+      TIMELINE_LIMIT_DAILY = 7;
     };
   };
   services.snapper.snapshotInterval = "*:0/5";