diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
index 5d83f69abd44..53ffa9047f16 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
@@ -21,6 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  */
 
 #include <sys/zfs_context.h>
@@ -96,6 +97,15 @@ int metaslab_prefetch_limit = SPA_DVAS_PER_BP;
  */
 int metaslab_smo_bonus_pct = 150;
 
+/*
+ * Should we be willing to write data to degraded vdevs?
+ */
+boolean_t zfs_write_to_degraded = B_FALSE;
+SYSCTL_INT(_vfs_zfs, OID_AUTO, write_to_degraded, CTLFLAG_RW,
+    &zfs_write_to_degraded, 0,
+    "Allow writing data to degraded vdevs");
+TUNABLE_INT("vfs.zfs.write_to_degraded", &zfs_write_to_degraded);
+
 /*
  * ==========================================================================
  * Metaslab classes
@@ -1383,10 +1393,13 @@ metaslab_alloc_dva(spa_t *spa, metaslab_class_t *mc, uint64_t psize,
 
 		/*
 		 * Avoid writing single-copy data to a failing vdev
+		 * unless the user instructs us that it is okay.
 		 */
 		if ((vd->vdev_stat.vs_write_errors > 0 ||
 		    vd->vdev_state < VDEV_STATE_HEALTHY) &&
-		    d == 0 && dshift == 3) {
+		    d == 0 && dshift == 3 &&
+		    !(zfs_write_to_degraded && vd->vdev_state ==
+		    VDEV_STATE_DEGRADED)) {
 			all_zero = B_FALSE;
 			goto next;
 		}