Index: uspace/app/hrctl/hrctl.c
===================================================================
--- uspace/app/hrctl/hrctl.c	(revision d1d355f9820c7738d073714c023e911fa335637a)
+++ uspace/app/hrctl/hrctl.c	(revision ac4b70bf8312f968d622e8ccc709c20de51f7dcc)
@@ -71,5 +71,5 @@
     "\n"
     "  -m, --modify volume                       Modify a volume, options:\n"
-    "          -f, --fail index                  fail an extent, or\n"
+    "          -f, --fail index                  fail an extent (DANGEROUS), or\n"
     "          -h, --hotspare device             add hotspare.\n"
     "\n"
@@ -88,5 +88,9 @@
     "\t\thrctl -s\n"
     "\n"
-    "Volume service names are automatically prepended with \"devices/\" prefix.\n"
+    "Notes:\n"
+    "  Volume service names are automatically prepended with \"devices/\" prefix.\n"
+    "  Simulating an extent failure with -m volume -f index is dangerous. It marks\n"
+    "  metadata as dirty in other healthy extents, and therefore invalidates\n"
+    "  the specified extent.\n"
     "\n"
     "Limitations:\n"