Apply by doing:
        cd /usr/src
        patch -p0 < 006_scsi.patch

Then build and install a new kernel.

Index: sys/scsi/cd.c
===================================================================
RCS file: /cvs/src/sys/scsi/cd.c,v
retrieving revision 1.164
retrieving revision 1.164.2.1
diff -u -r1.164 -r1.164.2.1
--- sys/scsi/cd.c	28 Feb 2010 21:17:00 -0000	1.164
+++ sys/scsi/cd.c	6 Jul 2010 08:48:50 -0000	1.164.2.1
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cd.c,v 1.164 2010/02/28 21:17:00 krw Exp $	*/
+/*	$OpenBSD: cd.c,v 1.164.2.1 2010/07/06 08:48:50 stephan Exp $	*/
 /*	$NetBSD: cd.c,v 1.100 1997/04/02 02:29:30 mycroft Exp $	*/
 
 /*
@@ -683,6 +683,7 @@
 {
 	struct cd_softc *sc = xs->sc_link->device_softc;
 	struct buf *bp = xs->cookie;
+	int error;
 
 	splassert(IPL_BIO);
          
@@ -704,7 +705,13 @@
 
 	case XS_SENSE:
 	case XS_SHORTSENSE:
-		if (scsi_interpret_sense(xs) != ERESTART)
+		error = scsi_interpret_sense(xs);
+		if (error == 0) {
+			bp->b_error = 0;
+			bp->b_resid = xs->resid;
+			break;
+		}
+		if (error != ERESTART)
 			xs->retries = 0;
 		goto retry;
 
Index: sys/scsi/sd.c
===================================================================
RCS file: /cvs/src/sys/scsi/sd.c,v
retrieving revision 1.182
retrieving revision 1.182.2.1
diff -u -r1.182 -r1.182.2.1
--- sys/scsi/sd.c	15 Jan 2010 05:50:31 -0000	1.182
+++ sys/scsi/sd.c	6 Jul 2010 08:48:50 -0000	1.182.2.1
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sd.c,v 1.182 2010/01/15 05:50:31 krw Exp $	*/
+/*	$OpenBSD: sd.c,v 1.182.2.1 2010/07/06 08:48:50 stephan Exp $	*/
 /*	$NetBSD: sd.c,v 1.111 1997/04/02 02:29:41 mycroft Exp $	*/
 
 /*-
@@ -755,6 +755,7 @@
 {
 	struct sd_softc *sc = xs->sc_link->device_softc;
 	struct buf *bp = xs->cookie;
+	int error;
 
 	splassert(IPL_BIO);
 
@@ -776,7 +777,13 @@
 
 	case XS_SENSE:
 	case XS_SHORTSENSE:
-		if (scsi_interpret_sense(xs) != ERESTART)
+		error = scsi_interpret_sense(xs);
+		if (error == 0) {
+			bp->b_error = 0;
+			bp->b_resid = xs->resid;
+			break;
+		}
+		if (error != ERESTART)
 			xs->retries = 0;
 		goto retry;
 
Index: sys/scsi/st.c
===================================================================
RCS file: /cvs/src/sys/scsi/st.c,v
retrieving revision 1.93
retrieving revision 1.93.2.1
diff -u -r1.93 -r1.93.2.1
--- sys/scsi/st.c	15 Jan 2010 05:50:31 -0000	1.93
+++ sys/scsi/st.c	6 Jul 2010 08:48:50 -0000	1.93.2.1
@@ -1,4 +1,4 @@
-/*	$OpenBSD: st.c,v 1.93 2010/01/15 05:50:31 krw Exp $	*/
+/*	$OpenBSD: st.c,v 1.93.2.1 2010/07/06 08:48:50 stephan Exp $	*/
 /*	$NetBSD: st.c,v 1.71 1997/02/21 23:03:49 thorpej Exp $	*/
 
 /*
@@ -1088,6 +1088,7 @@
 {
 	struct st_softc *st = xs->sc_link->device_softc;
 	struct buf *bp = xs->cookie;
+	int error;
 
 	splassert(IPL_BIO);
 
@@ -1107,7 +1108,13 @@
 
 	case XS_SENSE:
 	case XS_SHORTSENSE:
-		if (scsi_interpret_sense(xs) != ERESTART)
+		error = scsi_interpret_sense(xs);
+		if (error == 0) {
+			bp->b_error = 0;
+			bp->b_resid = xs->resid;
+			break;
+		}
+		if (error != ERESTART)
 			xs->retries = 0;
 		goto retry;