diff --git a/cmd/zed/zed.d/io-spare.sh b/cmd/zed/zed.d/io-spare.sh
index dd5bf4e0f226..7ff91cae3934 100755
--- a/cmd/zed/zed.d/io-spare.sh
+++ b/cmd/zed/zed.d/io-spare.sh
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 #
 # Replace a device with a hot spare in response to IO or checksum errors.
 # The following actions will be performed automatically when the number
@@ -38,9 +38,11 @@ test -n "${ZEVENT_VDEV_GUID}" || exit 5
 # Defaults to disabled, enable in the zed.rc file.
 ZED_SPARE_ON_IO_ERRORS=${ZED_SPARE_ON_IO_ERRORS:-0}
 ZED_SPARE_ON_CHECKSUM_ERRORS=${ZED_SPARE_ON_CHECKSUM_ERRORS:-0}
+ZED_SPARE_ON_UNAVAIL=${ZED_SPARE_ON_UNAVAIL:-0}
 
 if [ ${ZED_SPARE_ON_IO_ERRORS} -eq 0 -a \
-     ${ZED_SPARE_ON_CHECKSUM_ERRORS} -eq 0 ]; then
+     ${ZED_SPARE_ON_CHECKSUM_ERRORS} -eq 0 -a \
+     ${ZED_SPARE_ON_UNAVAIL} -eq 0 ]; then
 	exit 2
 fi
 
@@ -61,6 +63,17 @@ vdev_status() {
 	return 0
 }
 
+# Given a <device>, return the size
+vdev_size() {
+	local VDEV=`basename $1`
+
+	for dir in /dev /dev/disk/by-*; do
+		if [[ -L $dir/$VDEV ]]; then
+			blockdev --getsize64  $dir/$VDEV
+		fi
+	done
+}
+
 # Fault devices after N I/O errors.
 if [ "${ZEVENT_CLASS}" = "ereport.fs.zfs.io" ]; then
 	ERRORS=`expr ${ZEVENT_VDEV_READ_ERRORS} + ${ZEVENT_VDEV_WRITE_ERRORS}`
@@ -69,6 +82,7 @@ if [ "${ZEVENT_CLASS}" = "ereport.fs.zfs.io" ]; then
 	     ${ERRORS} -ge ${ZED_SPARE_ON_IO_ERRORS} ]; then
 		ACTION="fault"
 	fi
+
 # Degrade devices after N checksum errors.
 elif [ "${ZEVENT_CLASS}" = "ereport.fs.zfs.checksum" ]; then
 	ERRORS=${ZEVENT_VDEV_CKSUM_ERRORS}
@@ -77,12 +91,12 @@ elif [ "${ZEVENT_CLASS}" = "ereport.fs.zfs.checksum" ]; then
 	     ${ERRORS} -ge ${ZED_SPARE_ON_CHECKSUM_ERRORS} ]; then
 		ACTION="degrade"
 	fi
+
 else
 	ACTION=
 fi
 
 if [ -n "${ACTION}" ]; then
-
 	# Device is already FAULTED or DEGRADED
 	set -- `vdev_status ${ZEVENT_POOL} ${ZEVENT_VDEV_PATH}`
 	ZEVENT_VDEV_PATH_FOUND=$1
@@ -110,10 +124,17 @@ if [ -n "${ACTION}" ]; then
 	# Round robin through the spares selecting those which are available.
 	#
 	for SPARE in ${ZEVENT_VDEV_SPARE_PATHS}; do
+		orig_size=${ZEVENT_VDEV_SIZE}
+		spare_size=$(vdev_size ${SPARE})
+		echo "${SPARE}: orig_size='$orig_size', spare_size='$spare_size'" >> /tmp/zed.out
+
 		set -- `vdev_status ${ZEVENT_POOL} ${SPARE}`
 		SPARE_VDEV_FOUND=$1
 		STATUS=$2
+		echo "SPARE_VDEV_FOUND='$SPARE_VDEV_FOUND', STATUS='$STATUS'" >> /tmp/zed.out
+
 		if [ "${STATUS}" = "AVAIL" ]; then
+			echo "${ZPOOL} replace ${ZEVENT_POOL} ${ZEVENT_VDEV_GUID} ${SPARE_VDEV_FOUND}" >> /tmp/zed.out
 			${ZPOOL} replace ${ZEVENT_POOL} \
 			    ${ZEVENT_VDEV_GUID} ${SPARE_VDEV_FOUND} && exit 0
 		fi
diff --git a/include/sys/fm/fs/zfs.h b/include/sys/fm/fs/zfs.h
index d541b07a3729..cb039dd1042a 100644
--- a/include/sys/fm/fs/zfs.h
+++ b/include/sys/fm/fs/zfs.h
@@ -73,6 +73,7 @@ extern "C" {
 #define	FM_EREPORT_PAYLOAD_ZFS_VDEV_FRU		"vdev_fru"
 #define	FM_EREPORT_PAYLOAD_ZFS_VDEV_STATE	"vdev_state"
 #define	FM_EREPORT_PAYLOAD_ZFS_VDEV_ASHIFT	"vdev_ashift"
+#define	FM_EREPORT_PAYLOAD_ZFS_VDEV_SIZE	"vdev_size"
 #define	FM_EREPORT_PAYLOAD_ZFS_VDEV_COMP_TS	"vdev_complete_ts"
 #define	FM_EREPORT_PAYLOAD_ZFS_VDEV_DELTA_TS	"vdev_delta_ts"
 #define	FM_EREPORT_PAYLOAD_ZFS_VDEV_SPARE_PATHS	"vdev_spare_paths"
diff --git a/man/man5/zfs-events.5 b/man/man5/zfs-events.5
index 4b72484d4f1c..a25f2419bb0d 100644
--- a/man/man5/zfs-events.5
+++ b/man/man5/zfs-events.5
@@ -383,6 +383,16 @@ The GUID of the vdev in question (the vdev failing or operated upon with
 \fBzpool clear\fR etc).
 .RE
 
+.sp
+.ne 2
+.na
+\fBvdev_size\fR
+.ad
+.RS 12n
+Size of the vdev in question (the vdev failing or operated upon with
+\fBzpool clear\fR etc).
+.RE
+
 .sp
 .ne 2
 .na
diff --git a/module/zfs/zfs_fm.c b/module/zfs/zfs_fm.c
index fb65ec6a6525..fd8233d8f020 100644
--- a/module/zfs/zfs_fm.c
+++ b/module/zfs/zfs_fm.c
@@ -312,7 +312,9 @@ zfs_ereport_start(nvlist_t **ereport_out, nvlist_t **detector_out,
 			if (pvd->vdev_path)
 				fm_payload_set(ereport,
 				    FM_EREPORT_PAYLOAD_ZFS_PARENT_PATH,
-				    DATA_TYPE_STRING, pvd->vdev_path, NULL);
+				    DATA_TYPE_STRING, pvd->vdev_path,
+				    FM_EREPORT_PAYLOAD_ZFS_VDEV_SIZE,
+				    DATA_TYPE_UINT64, pvd->vdev_psize, NULL);
 			if (pvd->vdev_devid)
 				fm_payload_set(ereport,
 				    FM_EREPORT_PAYLOAD_ZFS_PARENT_DEVID,