diff --git a/docu/mars-manual.lyx b/docu/mars-manual.lyx
index 3fcfd0ff..17330263 100644
--- a/docu/mars-manual.lyx
+++ b/docu/mars-manual.lyx
@@ -2479,8 +2479,8 @@ guaranteed
 \family typewriter
 fake-sync
 \family default
-, you may startover the fast full sync at your secondary side at any time
- by saying 
+, you may startover the fast full sync at your secondary side by saying
+ 
 \family typewriter
 marsadm invalidate mydata
 \family default
@@ -16265,8 +16265,9 @@ $res
 \family default
  must denote an already existing resource in the cluster (i.e.
  its symlink tree information must have been received).
- The resource must have a designated primary, and there must not exist a
- split brain.
+ The resource must have a designated primary, and it must no be in emergency
+ mode.
+ There must not exist a split brain in the cluster.
  The local node must not be already member of that resource.
  The argument 
 \family typewriter
@@ -18107,7 +18108,8 @@ status open
 \begin_layout Plain Layout
 
 \size scriptsize
-Precondition: none additionally.
+Precondition: additionally, a primary must be designated, and it must not
+ be in emergency mode.
 \end_layout
 
 \begin_layout Plain Layout
@@ -21192,9 +21194,9 @@ reference "sub:Split-Brain-Resolution"
 \family typewriter
 marsadm invalidate
 \family default
- cannot resolve a split brain at other secondaries (which are neither the
- old nor the new designated primary).
- Therefore, use the 
+ cannot always resolve a split brain at other secondaries (which are neither
+ the old nor the new designated primary).
+ Therefore, prefer the 
 \family typewriter
 leave-resource
 \family default
@@ -26782,7 +26784,7 @@ status open
 \begin_layout Plain Layout
 
 \size scriptsize
-This is too dangerous in case you have multiple secondaries.
+This would be too dangerous in case you have multiple secondaries.
  A similar effect can be achieved with the 
 \family typewriter
 --host=
diff --git a/userspace/marsadm b/userspace/marsadm
index 49e116cc..3fea54a7 100755
--- a/userspace/marsadm
+++ b/userspace/marsadm
@@ -571,6 +571,19 @@ sub check_userspace {
   }
 }
 
+sub check_sync_startable {
+  my ($cmd, $res) = @_;
+  my $primary = _get_designated_primary($res);
+  ldie "Cannot execute '$cmd' because noone is designated as primary.\n" if (!$primary || $primary eq "(none)");
+  # no danger when switch is turned on at the primary side.
+  return if $primary eq $host;
+  my $emergency_path = "$mars/resource-$res/actual-$primary/has-emergency";
+  my $emergency = get_link($emergency_path, 1);
+  if ($emergency) {
+    ldie "Primary '$primary' is in emergency mode. Cannot start sync.\nFree some space there first.\n";
+  }
+}
+
 ##################################################################
 
 # state inspection routines
@@ -1456,6 +1469,7 @@ sub create_res {
     ldie "Sorry, joining is only possible if a designated primary exists.\n" if $primary eq "(none)";
     ldie "implausible state: I ($host) am already designated primary of resource '$res' which I just wanted to join\n" if $primary eq $host;
     ldie "my ip '$ip' is not registered -- please run 'join-cluster' first\n" unless -l "$mars/ips/ip-$host";
+    check_sync_startable(@_);
     my $replay = get_link("$resdir/replay-$primary");
     if ($replay =~ m/^log-([0-9]+)-/) {
       $replay_nr = $1;
@@ -1808,6 +1822,7 @@ sub fetch_local_res {
 sub pause_sync_global_res {
   my ($cmd, $res) = @_;
   my $pause = ($cmd =~ m/pause/);
+  check_sync_startable(@_) if !$pause;
   my @paths = glob("$mars/resource-$res/todo-*/");
   for my $path (@paths) {
     _switch($cmd, $res, "$path/sync", !$pause);
@@ -1817,6 +1832,7 @@ sub pause_sync_global_res {
 sub pause_sync_local_res {
   my ($cmd, $res) = @_;
   my $pause = ($cmd =~ m/pause/);
+  check_sync_startable(@_) if !$pause;
   my $path = "$mars/resource-$res/todo-$host/sync";
   _switch($cmd, $res, $path, !$pause);
 }
@@ -2093,7 +2109,14 @@ sub invalidate_res_phase3 {
   _switch($cmd, $res, "$mars/resource-$res/todo-$host/attach", 1);
   _switch($cmd, $res, "$mars/resource-$res/todo-$host/fetch", 1);
   _switch($cmd, $res, "$mars/resource-$res/todo-$host/replay", 1);
-  _switch($cmd, $res, "$mars/resource-$res/todo-$host/sync", 1);
+  finish_links();
+  my $emergency_path = "$mars/resource-$res/actual-$primary/has-emergency";
+  my $emergency = get_link($emergency_path, 1);
+  if ($emergency) {
+    lwarn "Primary '$primary' is in emergency mode. Cannot start sync.\n";
+  } else {
+    _switch($cmd, $res, "$mars/resource-$res/todo-$host/sync", 1);
+  }
 }
 
 sub resize_res {