Add btrbk

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/configs/system/btrbk/default.nix

@@ -0,0 +1,33 @@
+{ ... }:
+{
+  systemd.tmpfiles.rules = [
+    "d /persist/user.bak 0755 root root"
+    "d /persist/state.bak 0755 root root"
+  ];
+
+  services.btrbk = {
+    ioSchedulingClass = "idle";
+    niceness = 19;
+    instances = {
+      persist-user = {
+        onCalendar = "hourly";
+        settings.volume."/persist" = {
+          subvolume = "user";
+          snapshot_dir = "user.bak";
+          snapshot_preserve_min = "latest";
+          snapshot_preserve = "48h 14d 4w 6m";
+        };
+      };
+
+      persist-state = {
+        onCalendar = "daily";
+        settings.volume."/persist" = {
+          subvolume = "state";
+          snapshot_dir = "state.bak";
+          snapshot_preserve_min = "latest";
+          snapshot_preserve = "7d 4w 3m";
+        };
+      };
+    };
+  };
+}