Add verify_dump option to control whether to dump bad/good blocks or not

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/HOWTO b/HOWTO
index 1915bd6..68e17e9 100644
--- a/HOWTO
+++ b/HOWTO
@@ -926,6 +926,11 @@
 		option is set, fio will exit the job on the first observed
 		failure.
 
+verify_dump=bool	If set, dump the contents of both the original data
+		block and the data block we read off disk to files. This
+		allows later analysis to inspect just what kind of data
+		corruption occurred. On by default.
+
 verify_async=int	Fio will normally verify IO inline from the submitting
 		thread. This option takes an integer describing how many
 		async offload threads to create for IO verification instead,