diff --git a/src/PVE/Storage/Plugin.pm b/src/PVE/Storage/Plugin.pm
index ae97dfb..23cc95d 100644
--- a/src/PVE/Storage/Plugin.pm
+++ b/src/PVE/Storage/Plugin.pm
@@ -2437,9 +2437,13 @@ sub new_backup_provider {
 
 Returns a string with the type of snapshot that qemu can do for a specific volume
 
-'internal' : support snapshot with qemu internal snapshot
-'external' : support snapshot with qemu external snapshot
-undef      : don't support qemu snapshot
+'qemu'    : Qemu must perform the snapshot. The storage plugin does nothing.
+'mixed'   : The storage plugin *transparently* performs the snapshot and the running VM does not
+            need to do anything.
+'storage' : The storage performs an offline snapshot and qemu then has to reopen the volume.
+            Qemu will either "unhook" the snapshot by moving its data into the child snapshot
+            or Qemu will "commit" the child snapshot to the one which is being removed. Both must
+            be supported.
 =cut
 
 sub volume_qemu_snapshot_method {