diff --git a/modules/nixos/base/btrbk.nix b/modules/nixos/base/btrbk.nix
index 62718223..181e1190 100644
--- a/modules/nixos/base/btrbk.nix
+++ b/modules/nixos/base/btrbk.nix
@@ -18,7 +18,7 @@
 
   services.btrbk.instances.btrbk = {
     # How often this btrbk instance is started. See systemd.time(7) for more information about the format.
-    onCalendar = "Tue,Fri,Sat,Sun *-*-* 3:45:20"; # daily at 3:45, except on Monday, Wednesday, and Thursday
+    onCalendar = "Tue,Thu,Sat *-*-* 3:45:20";
     settings = {
       # how to prune local snapshots:
       # 1. keep daily snapshots for xx days
diff --git a/modules/nixos/server/kubevirt-hardware-configuration.nix b/modules/nixos/server/kubevirt-hardware-configuration.nix
index 84d4832f..4a9c02ef 100644
--- a/modules/nixos/server/kubevirt-hardware-configuration.nix
+++ b/modules/nixos/server/kubevirt-hardware-configuration.nix
@@ -18,6 +18,12 @@
     "${toString modulesPath}/profiles/qemu-guest.nix"
   ];
 
+  # backup only once a week inside all virtual machines
+  services.btrbk.instances.btrbk = {
+    onCalendar = lib.mkForce "Wed *-*-* 5:25:20";
+    settings.snapshot_preserve = lib.mkForce "7d";
+  };
+
   config = {
     fileSystems."/" = {
       device = "/dev/disk/by-label/nixos";