diff --git a/PVE/QemuConfig.pm b/PVE/QemuConfig.pm
index b2d4e454..8fae4fc6 100644
--- a/PVE/QemuConfig.pm
+++ b/PVE/QemuConfig.pm
@@ -138,6 +138,10 @@ sub __snapshot_save_vmstate {
     }
 
     my $driver_state_size = 500; # assume 500MB is enough to safe all driver state;
+    # our savevm-start does live-save of the memory until the space left in the
+    # volume is just enough for the remaining memory content + internal state
+    # then it stops the vm and copies the rest so we reserve twice the
+    # memory content + state to minimize vm downtime
     my $size = $conf->{memory}*2 + $driver_state_size;
     my $scfg = PVE::Storage::storage_config($storecfg, $target);