diff --git a/lustre-iokit/sgpdd-survey/README.sgpdd-survey b/lustre-iokit/sgpdd-survey/README.sgpdd-survey
index 8fb5c97fad69fcf9d67b43bf9904e73079be437b..4b95eda10f169b1d6b291c04e208c02890757142 100644
--- a/lustre-iokit/sgpdd-survey/README.sgpdd-survey
+++ b/lustre-iokit/sgpdd-survey/README.sgpdd-survey
@@ -34,6 +34,11 @@ SCSI device:
 	(make sure the kernel module "sg" is loaded)
 Raw device:
 	Must appear in the output of 'raw -qa'
+
+	If you need to create raw devices in order to use this tool, note that
+	raw device 0 can not be used due to a bug in certain versions of the
+	"raw" utility (including that shipped with RHEL4U4.)
+
 You may not mix raw and SCSI devices in the test specification.