periodically balance

hosts/nas/services.nix

@@ -230,6 +230,30 @@ in
   };
 
   systemd.services = {
+    btrfs-balance = {
+      description = "BTRFS Balance Service";
+      # This ensures the service only runs when the filesystem is mounted
+      requires = [ "local-fs.target" ];
+      after = [ "local-fs.target" ];
+      
+      # The actual balance command
+      script = ''
+        # Start with lower usage to handle the most fragmented blocks first
+        ${pkgs.btrfs-progs}/bin/btrfs balance start -dusage=5 -musage=5 /mount/point
+        ${pkgs.btrfs-progs}/bin/btrfs balance start -dusage=10 -musage=10 /mount/point
+        ${pkgs.btrfs-progs}/bin/btrfs balance start -dusage=20 -musage=20 /mount/point
+      '';
+
+      serviceConfig = {
+        Type = "oneshot";
+        Nice = 19;  # Lowest CPU priority
+        IOSchedulingClass = "idle";  # Lowest I/O priority
+        # Prevent multiple instances from running simultaneously
+        ExecStartPre = "${pkgs.coreutils}/bin/rm -f /var/run/btrfs-balance.stamp";
+        ExecStopPost = "${pkgs.coreutils}/bin/touch /var/run/btrfs-balance.stamp";
+      };
+    };
+    
     system-update-check = {
       description = "Check for system configuration updates";
 
@@ -314,15 +338,30 @@ in
   };
 
   # Create a timer to run the service periodically
-  systemd.timers.system-update-check = {
-    description = "Timer for system configuration updates";
-    wantedBy = [ "timers.target" ];
-    
-    # Timer configuration
-    timerConfig = {
-      OnCalendar = "daily";  # Check every day
-      Persistent = true;      # Run immediately if last run was missed
-      Unit = "system-update-check.service";
+  systemd.timers = {
+    btrfs-balance = {
+      description = "Timer for BTRFS Balance Service";
+      wantedBy = [ "timers.target" ];
+      
+      timerConfig = {
+        # Run weekly on Sunday at 2am
+        OnCalendar = "Sun *-*-* 02:00:00";
+        # Add randomized delay to prevent multiple systems from starting at exactly the same time
+        RandomizedDelaySec = "1h";
+        # Ensure we don't start multiple times if the system was off
+        Persistent = true;
+      };
+    };
+    system-update-check = {
+      description = "Timer for system configuration updates";
+      wantedBy = [ "timers.target" ];
+      
+      # Timer configuration
+      timerConfig = {
+        OnCalendar = "daily";  # Check every day
+        Persistent = true;      # Run immediately if last run was missed
+        Unit = "system-update-check.service";
+      };
     };
   };
 }