diff --git a/docu/mars-manual.lyx b/docu/mars-manual.lyx
index 8dbdb279..d15e8bf3 100644
--- a/docu/mars-manual.lyx
+++ b/docu/mars-manual.lyx
@@ -8596,6 +8596,47 @@ reference "sub:Emergency-Mode"
 ).
 \end_layout
 
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+
+\family typewriter
+disk-size
+\family default
+ Show the size of the underlying local disk in bytes.
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+
+\family typewriter
+resource-size
+\family default
+ Show the logical size of the resource in bytes.
+ When this value is lower than 
+\family typewriter
+disk-size
+\family default
+, you are wasting space.
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+
+\family typewriter
+device-size
+\family default
+ At a primary node, this may differ from 
+\family typewriter
+resource-size
+\family default
+ only for a very short time during the 
+\family typewriter
+resize
+\family default
+ operation.
+ At secondaries, there will be no difference.
+\end_layout
+
 \begin_layout Standard
 \noindent
 The following macros are only meaningful for secondary nodes.
diff --git a/userspace/marsadm b/userspace/marsadm
index 5c02a0cf..a06a8992 100755
--- a/userspace/marsadm
+++ b/userspace/marsadm
@@ -3113,6 +3113,20 @@ sub eval_fn {
       }
       return $sum;
     }
+    if (/^(disk|resource|device)[-_]?size$/) {
+      my $what = $1;
+      my $path = "$mars/resource-" . $$env{"res"};
+      if ($what eq "device" && eval_fn($env, "present-device", "")) {
+	return _get_mars_size($$env{"cmd"}, $$env{"res"});
+      } elsif ($what eq "disk"){
+	my $peer = parse_macro($arg1, $env);
+	$peer = $$env{"host"} unless $peer;
+	$path .= "/actsize-$peer";
+      } else {
+	$path .= "/size";
+      }
+      return get_link($path, 1);
+    }
     # time handling and pausing
     if (/^time$/) {
       return mars_time();
@@ -3884,6 +3898,8 @@ my %trivial_globs =
    => "",
 
    # intended for scripting
+   "{disk,resource,device}-size"
+   => "",
    "deletable-size"
    => "",
    "occupied-size"