--- sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_mirror.c.orig	2010-05-12 12:18:06.268124859 +0200
+++ sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_mirror.c	2010-05-12 12:20:11.412140369 +0200
@@ -219,7 +219,7 @@
 		mc = &mm->mm_child[c];
 		if (mc->mc_tried || mc->mc_skipped)
 			continue;
-		if (!vdev_readable(mc->mc_vd)) {
+		if (mc->mc_vd == NULL || !vdev_readable(mc->mc_vd)) {
 			mc->mc_error = ENXIO;
 			mc->mc_tried = 1;	/* don't even try */
 			mc->mc_skipped = 1;