Rdbfs retries were broken; after the first retry attempt, a resend would never occur. If the maximum number of retries are exhausted, a client would also hang due to a missing Rread.
--- /n/sourcesdump/2012/0926/plan9/sys/src/cmd/rdbfs.c	Tue Mar 14 13:16:59 2006
+++ /sys/src/cmd/rdbfs.c	Wed Sep 26 00:00:00 2012
@@ -223,9 +223,11 @@
 					goto Break2;
 				}else{
 					DBG(2, "unknown message\n");
+					break;
 				}
 			}
 		}
+		respond(r, "timed out");
 	Break2:;
 	}
 }