OpenZFS 9075 - Improve ZFS pool import/load process and corrupted pool recovery

Some work has been done lately to improve the debugability of the ZFS pool
load (and import) process. This includes:

	7638 Refactor spa_load_impl into several functions
	8961 SPA load/import should tell us why it failed
	7277 zdb should be able to print zfs_dbgmsg's

To iterate on top of that, there's a few changes that were made to make the
import process more resilient and crash free. One of the first tasks during the
pool load process is to parse a config provided from userland that describes
what devices the pool is composed of. A vdev tree is generated from that config,
and then all the vdevs are opened.

The Meta Object Set (MOS) of the pool is accessed, and several metadata objects
that are necessary to load the pool are read. The exact configuration of the
pool is also stored inside the MOS. Since the configuration provided from
userland is external and might not accurately describe the vdev tree
of the pool at the txg that is being loaded, it cannot be relied upon to safely
operate the pool. For that reason, the configuration in the MOS is read early
on. In the past, the two configurations were compared together and if there was
a mismatch then the load process was aborted and an error was returned.

The latter was a good way to ensure a pool does not get corrupted, however it
made the pool load process needlessly fragile in cases where the vdev
configuration changed or the userland configuration was outdated. Since the MOS
is stored in 3 copies, the configuration provided by userland doesn't have to be
perfect in order to read its contents. Hence, a new approach has been adopted:
The pool is first opened with the untrusted userland configuration just so that
the real configuration can be read from the MOS. The trusted MOS configuration
is then used to generate a new vdev tree and the pool is re-opened.

When the pool is opened with an untrusted configuration, writes are disabled
to avoid accidentally damaging it. During reads, some sanity checks are
performed on block pointers to see if each DVA points to a known vdev;
when the configuration is untrusted, instead of panicking the system if those
checks fail we simply avoid issuing reads to the invalid DVAs.

This new two-step pool load process now allows rewinding pools accross
vdev tree changes such as device replacement, addition, etc. Loading a pool
from an external config file in a clustering environment also becomes much
safer now since the pool will import even if the config is outdated and didn't,
for instance, register a recent device addition.

With this code in place, it became relatively easy to implement a
long-sought-after feature: the ability to import a pool with missing top level
(i.e. non-redundant) devices. Note that since this almost guarantees some loss
of data, this feature is for now restricted to a read-only import.

Porting notes (ZTS):
* Fix 'make dist' target in zpool_import

* The maximum path length allowed by tar is 99 characters.  Several
  of the new test cases exceeded this limit resulting in them not
  being included in the tarball.  Shorten the names slightly.

* Set/get tunables using accessor functions.

* Get last synced txg via the "zfs_txg_history" mechanism.

* Clear zinject handlers in cleanup for import_cache_device_replaced
  and import_rewind_device_replaced in order that the zpool can be
  exported if there is an error.

* Increase FILESIZE to 8G in zfs-test.sh to allow for a larger
  ext4 file system to be created on ZFS_DISK2.  Also, there's
  no need to partition ZFS_DISK2 at all.  The partitioning had
  already been disabled for multipath devices.  Among other things,
  the partitioning steals some space from the ext4 file system,
  makes it difficult to accurately calculate the paramters to
  parted and can make some of the tests fail.

* Increase FS_SIZE and FILE_SIZE in the zpool_import test
  configuration now that FILESIZE is larger.

* Write more data in order that device evacuation take lonnger in
  a couple tests.

* Use mkdir -p to avoid errors when the directory already exists.

* Remove use of sudo in import_rewind_config_changed.

Authored by: Pavel Zakharov <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Andrew Stormont <[email protected]>
Approved by: Hans Rosenfeld <[email protected]>
Ported-by: Tim Chase <[email protected]>
Signed-off-by: Tim Chase <[email protected]>

OpenZFS-issue: https://illumos.org/issues/9075
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/619c0123
Closes #7459

14 files changed, 1690 insertions, 34 deletions

diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/Makefile.am b/tests/zfs-tests/tests/functional/cli_root/zpool_import/Makefile.am
index 8aa34f33c..97a15a20d 100644
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_import/Makefile.am
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/Makefile.am
@@ -2,6 +2,17 @@ pkgdatadir = $(datadir)/@PACKAGE@/zfs-tests/tests/functional/cli_root/zpool_impo
 dist_pkgdata_SCRIPTS = \
 	setup.ksh \
 	cleanup.ksh \
+	zpool_import.kshlib \
+	import_cache_device_added.ksh \
+	import_cache_device_removed.ksh \
+	import_cache_device_replaced.ksh \
+	import_cache_mirror_attached.ksh \
+	import_cache_mirror_detached.ksh \
+	import_cache_shared_device.ksh \
+	import_devices_missing.ksh \
+	import_paths_changed.ksh \
+	import_rewind_config_changed.ksh \
+	import_rewind_device_replaced.ksh \
 	zpool_import_001_pos.ksh \
 	zpool_import_002_pos.ksh \
 	zpool_import_003_pos.ksh \
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_added.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_added.ksh
new file mode 100755
index 000000000..bda6b891b
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_added.ksh
@@ -0,0 +1,76 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should be importable using an outdated cachefile that is unaware
+#	that one or two top-level vdevs were added.
+#
+# STRATEGY:
+#	1. Create a pool with some devices and an alternate cachefile.
+#	2. Backup the cachefile.
+#	3. Add a device/mirror/raid to the pool.
+#	4. Export the pool.
+#	5. Verify that we can import the pool using the backed-up cachefile.
+#
+
+verify_runnable "global"
+
+log_onexit cleanup
+
+function test_add_vdevs
+{
+	typeset poolcreate="$1"
+	typeset addvdevs="$2"
+	typeset poolcheck="$3"
+
+	log_note "$0: pool '$poolcreate', add $addvdevs."
+
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 $poolcreate
+
+	log_must cp $CPATH $CPATHBKP
+
+	log_must zpool add -f $TESTPOOL1 $addvdevs
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool import -c $CPATHBKP $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolcheck"
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	log_must rm -f $CPATH $CPATHBKP
+
+	log_note ""
+}
+
+test_add_vdevs "$VDEV0" "$VDEV1" "$VDEV0 $VDEV1"
+test_add_vdevs "$VDEV0 $VDEV1" "$VDEV2" "$VDEV0 $VDEV1 $VDEV2"
+test_add_vdevs "$VDEV0" "$VDEV1 $VDEV2" "$VDEV0 $VDEV1 $VDEV2"
+test_add_vdevs "$VDEV0" "mirror $VDEV1 $VDEV2" \
+    "$VDEV0 mirror $VDEV1 $VDEV2"
+test_add_vdevs "mirror $VDEV0 $VDEV1" "mirror $VDEV2 $VDEV3" \
+    "mirror $VDEV0 $VDEV1 mirror $VDEV2 $VDEV3"
+test_add_vdevs "$VDEV0" "raidz $VDEV1 $VDEV2 $VDEV3" \
+    "$VDEV0 raidz $VDEV1 $VDEV2 $VDEV3"
+test_add_vdevs "$VDEV0" "log $VDEV1" "$VDEV0 log $VDEV1"
+test_add_vdevs "$VDEV0 log $VDEV1" "$VDEV2" "$VDEV0 $VDEV2 log $VDEV1"
+test_add_vdevs "$VDEV0" "$VDEV1 log $VDEV2" "$VDEV0 $VDEV1 log $VDEV2"
+
+log_pass "zpool import -c cachefile_unaware_of_add passed."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_removed.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_removed.ksh
new file mode 100755
index 000000000..1d878b7a2
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_removed.ksh
@@ -0,0 +1,145 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should be importable using an outdated cachefile that is unaware
+#	that one or more vdevs were removed.
+#
+# STRATEGY:
+#	1. Create a pool with some devices and an alternate cachefile.
+#	2. Backup the cachefile.
+#	3. Remove device(s) from the pool and remove them.
+#	4. (Optionally) Add device(s) to pool.
+#	5. Export the pool.
+#	6. Verify that we can import the pool using the backed-up cachefile.
+#
+
+verify_runnable "global"
+
+function custom_cleanup
+{
+	cleanup
+}
+
+log_onexit custom_cleanup
+
+function test_remove_vdev
+{
+	typeset poolcreate="$1"
+	typeset removevdev="$2"
+	typeset poolcheck="$3"
+
+	log_note "$0: pool '$poolcreate', remove $2."
+
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 $poolcreate
+
+	log_must cp $CPATH $CPATHBKP
+
+	log_must zpool remove $TESTPOOL1 $removevdev
+	log_must wait_for_pool_config $TESTPOOL1 "$poolcheck"
+	log_must rm $removevdev
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool import -c $CPATHBKP $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolcheck"
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	log_must rm -f $CPATH $CPATHBKP
+	log_must mkfile $FILE_SIZE $removevdev
+
+	log_note ""
+}
+
+#
+# We have to remove top-level non-log vdevs one by one, else there is a high
+# chance pool will report busy and command will fail for the second vdev.
+#
+function test_remove_two_vdevs
+{
+	log_note "$0."
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 \
+	    $VDEV0 $VDEV1 $VDEV2 $VDEV3 $VDEV4
+
+	log_must cp $CPATH $CPATHBKP
+
+	log_must zpool remove $TESTPOOL1 $VDEV4
+	log_must wait_for_pool_config $TESTPOOL1 \
+	    "$VDEV0 $VDEV1 $VDEV2 $VDEV3"
+	log_must zpool remove $TESTPOOL1 $VDEV3
+	log_must wait_for_pool_config $TESTPOOL1 "$VDEV0 $VDEV1 $VDEV2"
+	log_must rm $VDEV3 $VDEV4
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool import -c $CPATHBKP $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$VDEV0 $VDEV1 $VDEV2"
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	log_must rm -f $CPATH $CPATHBKP
+	log_must mkfile $FILE_SIZE $VDEV3 $VDEV4
+
+	log_note ""
+}
+
+#
+# We want to test the case where a whole created by a log device is filled
+# by a regular device
+#
+function test_remove_log_then_add_vdev
+{
+	log_note "$0."
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 \
+	    $VDEV0 $VDEV1 $VDEV2 log $VDEV3
+
+	log_must cp $CPATH $CPATHBKP
+
+	log_must zpool remove $TESTPOOL1 $VDEV1
+	log_must wait_for_pool_config $TESTPOOL1 "$VDEV0 $VDEV2 log $VDEV3"
+	log_must zpool remove $TESTPOOL1 $VDEV3
+	log_must check_pool_config $TESTPOOL1 "$VDEV0 $VDEV2"
+	log_must rm $VDEV1 $VDEV3
+	log_must zpool add $TESTPOOL1 $VDEV4
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool import -c $CPATHBKP $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$VDEV0 $VDEV2 $VDEV4"
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	log_must rm -f $CPATH $CPATHBKP
+	log_must mkfile $FILE_SIZE $VDEV1 $VDEV3
+
+	log_note ""
+}
+
+test_remove_vdev "$VDEV0 $VDEV1 $VDEV2" "$VDEV2" "$VDEV0 $VDEV1"
+test_remove_vdev "$VDEV0 $VDEV1 $VDEV2" "$VDEV1" "$VDEV0 $VDEV2"
+test_remove_vdev "$VDEV0 log $VDEV1" "$VDEV1" "$VDEV0"
+test_remove_vdev "$VDEV0 log $VDEV1 $VDEV2" "$VDEV1 $VDEV2" "$VDEV0"
+test_remove_vdev "$VDEV0 $VDEV1 $VDEV2 log $VDEV3" "$VDEV2" \
+    "$VDEV0 $VDEV1 log $VDEV3"
+test_remove_two_vdevs
+test_remove_log_then_add_vdev
+
+log_pass "zpool import -c cachefile_unaware_of_remove passed."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_replaced.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_replaced.ksh
new file mode 100755
index 000000000..f2888a5bb
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_device_replaced.ksh
@@ -0,0 +1,166 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should be importable using an outdated cachefile that is unaware
+#	of a zpool replace operation at different stages in time.
+#
+# STRATEGY:
+#	1. Create a pool with some devices and an alternate cachefile.
+#	2. Backup the cachefile.
+#	3. Initiate device replacement, backup cachefile again and export pool.
+#	   Special care must be taken so that resilvering doesn't complete
+#	   before we exported the pool.
+#	4. Verify that we can import the pool using the first cachefile backup.
+#	   (Test 1. cachefile: pre-replace, pool: resilvering)
+#	5. Wait for the resilvering to finish and export the pool.
+#	6. Verify that we can import the pool using the first cachefile backup.
+#	   (Test 2. cachefile: pre-replace, pool: post-replace)
+#	7. Export the pool.
+#	8. Verify that we can import the pool using the second cachefile backup.
+#	   (Test 3. cachefile: resilvering, pool: post-replace)
+#
+# STRATEGY TO SLOW DOWN RESILVERING:
+#	1. Reduce zfs_txg_timeout, which controls how long can we resilver for
+#	   each sync.
+#	2. Add data to pool
+#	3. Re-import the pool so that data isn't cached
+#	4. Use zinject to slow down device I/O
+#	5. Trigger the resilvering
+#	6. Use spa freeze to stop writing to the pool.
+#	7. Clear zinject events (needed to export the pool)
+#	8. Export the pool
+#
+
+verify_runnable "global"
+
+ZFS_TXG_TIMEOUT=""
+
+function custom_cleanup
+{
+	# Revert zfs_txg_timeout to defaults
+	[[ -n ZFS_TXG_TIMEOUT ]] &&
+	    log_must set_zfs_txg_timeout $ZFS_TXG_TIMEOUT
+
+	zinject -c all
+	cleanup
+}
+
+log_onexit custom_cleanup
+
+function test_replacing_vdevs
+{
+	typeset poolcreate="$1"
+	typeset replacevdev="$2"
+	typeset replaceby="$3"
+	typeset poolfinalstate="$4"
+	typeset zinjectdevices="$5"
+	typeset earlyremove="$6"
+	typeset writedata="$7"
+
+	log_note "$0: pool '$poolcreate', replace $replacevdev by $replaceby."
+
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 $poolcreate
+
+	# Cachefile: pool in pre-replace state
+	log_must cp $CPATH $CPATHBKP
+
+	# Steps to insure resilvering happens very slowly.
+	log_must write_some_data $TESTPOOL1 $writedata
+	log_must zpool export $TESTPOOL1
+	log_must cp $CPATHBKP $CPATH
+	log_must zpool import -c $CPATH -o cachefile=$CPATH $TESTPOOL1
+	typeset device
+	for device in $zinjectdevices ; do
+		log_must zinject -d $device -D 200:1 $TESTPOOL1 > /dev/null
+	done
+	log_must zpool replace $TESTPOOL1 $replacevdev $replaceby
+
+	# Cachefile: pool in resilvering state
+	log_must cp $CPATH $CPATHBKP2
+
+	# We must disable zinject in order to export the pool, so we freeze
+	# it first to prevent writing out subsequent resilvering progress.
+	log_must zpool freeze $TESTPOOL1
+	# Confirm pool is still replacing
+	log_must pool_is_replacing $TESTPOOL1
+	log_must zinject -c all > /dev/null
+	log_must zpool export $TESTPOOL1
+
+	( $earlyremove ) && log_must rm $replacevdev
+
+	############################################################
+	# Test 1. Cachefile: pre-replace, pool: resilvering
+	############################################################
+	log_must cp $CPATHBKP $CPATH
+	log_must zpool import -c $CPATH $TESTPOOL1
+
+	# Wait for resilvering to finish
+	log_must wait_for_pool_config $TESTPOOL1 "$poolfinalstate"
+	log_must zpool export $TESTPOOL1
+
+	( ! $earlyremove ) && log_must rm $replacevdev
+
+	############################################################
+	# Test 2. Cachefile: pre-replace, pool: post-replace
+	############################################################
+	log_must zpool import -c $CPATHBKP $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolfinalstate"
+	log_must zpool export $TESTPOOL1
+
+	############################################################
+	# Test 3. Cachefile: resilvering, pool: post-replace
+	############################################################
+	log_must zpool import -c $CPATHBKP2 $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolfinalstate"
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	log_must rm -f $CPATH $CPATHBKP $CPATHBKP2
+	log_must mkfile $FILE_SIZE $replacevdev
+
+	log_note ""
+}
+
+# We set zfs_txg_timeout to 1 to reduce resilvering time at each sync.
+ZFS_TXG_TIMEOUT=$(get_zfs_txg_timeout)
+set_zfs_txg_timeout 1
+
+test_replacing_vdevs "$VDEV0 $VDEV1" \
+    "$VDEV1" "$VDEV2" \
+    "$VDEV0 $VDEV2" \
+    "$VDEV0 $VDEV1" \
+    false 20
+
+test_replacing_vdevs "mirror $VDEV0 $VDEV1" \
+	"$VDEV1" "$VDEV2" \
+	"mirror $VDEV0 $VDEV2" \
+	"$VDEV0 $VDEV1" \
+	true 10
+
+test_replacing_vdevs "raidz $VDEV0 $VDEV1 $VDEV2" \
+	"$VDEV1" "$VDEV3" \
+	"raidz $VDEV0 $VDEV3 $VDEV2" \
+	"$VDEV0 $VDEV1 $VDEV2" \
+	true 20
+
+set_zfs_txg_timeout $ZFS_TXG_TIMEOUT
+
+log_pass "zpool import -c cachefile_unaware_of_replace passed."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_mirror_attached.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_mirror_attached.ksh
new file mode 100755
index 000000000..987b745b9
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_mirror_attached.ksh
@@ -0,0 +1,72 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should be importable using an outdated cachefile that misses a
+#	mirror that was attached.
+#
+# STRATEGY:
+#	1. Create a pool with some devices and an alternate cachefile.
+#	2. Backup the cachefile.
+#	3. Attach a mirror to one of the devices in the pool.
+#	4. Export the pool.
+#	5. Verify that we can import the pool using the backed-up cachefile.
+#
+
+verify_runnable "global"
+
+log_onexit cleanup
+
+function test_attach_vdev
+{
+	typeset poolcreate="$1"
+	typeset attachto="$2"
+	typeset attachvdev="$3"
+	typeset poolcheck="$4"
+
+	log_note "$0: pool '$poolcreate', attach $attachvdev to $attachto."
+
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 $poolcreate
+
+	log_must cp $CPATH $CPATHBKP
+
+	log_must zpool attach $TESTPOOL1 $attachto $attachvdev
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool import -c $CPATHBKP $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolcheck"
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	log_must rm -f $CPATH $CPATHBKP
+
+	log_note ""
+}
+
+test_attach_vdev "$VDEV0" "$VDEV0" "$VDEV4" "mirror $VDEV0 $VDEV4"
+test_attach_vdev "$VDEV0 $VDEV1" "$VDEV1" "$VDEV4" \
+    "$VDEV0 mirror $VDEV1 $VDEV4"
+test_attach_vdev "mirror $VDEV0 $VDEV1" "$VDEV0" "$VDEV4" \
+    "mirror $VDEV0 $VDEV1 $VDEV4"
+test_attach_vdev "$VDEV0 log $VDEV1" "$VDEV1" "$VDEV4" \
+    "$VDEV0 log mirror $VDEV1 $VDEV4"
+
+log_pass "zpool import -c cachefile_unaware_of_attach passed."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_mirror_detached.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_mirror_detached.ksh
new file mode 100755
index 000000000..85ec51673
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_mirror_detached.ksh
@@ -0,0 +1,70 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should be importable using an outdated cachefile that is unaware
+#	that a mirror was detached.
+#
+# STRATEGY:
+#	1. Create a pool with some devices mirrored and an alternate cachefile.
+#	2. Backup the cachefile.
+#	3. Detach a mirror from the pool.
+#	4. Export the pool.
+#	5. Verify that we can import the pool using the backed-up cachefile.
+#
+
+verify_runnable "global"
+
+log_onexit cleanup
+
+function test_detach_vdev
+{
+	typeset poolcreate="$1"
+	typeset poolcheck="$2"
+
+	log_note "$0: pool '$poolcreate', detach $VDEV4."
+
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 $poolcreate
+
+	log_must cp $CPATH $CPATHBKP
+
+	log_must zpool detach $TESTPOOL1 $VDEV4
+	log_must rm -f $VDEV4
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool import -c $CPATHBKP $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolcheck"
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	log_must rm -f $CPATH $CPATHBKP
+	log_must mkfile $FILE_SIZE $VDEV4
+
+	log_note ""
+}
+
+test_detach_vdev "mirror $VDEV0 $VDEV4" "$VDEV0"
+test_detach_vdev "mirror $VDEV0 $VDEV4 mirror $VDEV1 $VDEV2" \
+    "$VDEV0 mirror $VDEV1 $VDEV2"
+test_detach_vdev "mirror $VDEV0 $VDEV1 $VDEV4" "mirror $VDEV0 $VDEV1"
+test_detach_vdev "$VDEV0 log mirror $VDEV1 $VDEV4" "$VDEV0 log $VDEV1"
+
+log_pass "zpool import -c cachefile_unaware_of_detach passed."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_shared_device.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_shared_device.ksh
new file mode 100755
index 000000000..66225c11b
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_cache_shared_device.ksh
@@ -0,0 +1,113 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should not try to write to a device that doesn't belong to it
+#	anymore, even if the device is in its cachefile.
+#
+# STRATEGY:
+#	1. Create pool1 with some devices and an alternate cachefile.
+#	2. Backup the cachefile.
+#	3. Export pool1.
+#	4. Create pool2 using a device that belongs to pool1.
+#	5. Export pool2.
+#	6. Compute checksum of the shared device.
+#	7. Import pool1 and write some data to it.
+#	8. Verify that the checksum of the shared device hasn't changed.
+#
+
+verify_runnable "global"
+
+function custom_cleanup
+{
+	destroy_pool $TESTPOOL2
+	cleanup
+}
+
+log_onexit custom_cleanup
+
+function dev_checksum
+{
+	typeset dev="$1"
+	typeset checksum
+
+	log_note "Compute checksum of '$dev'"
+
+	checksum=$(md5sum $dev)
+	if [[ $? -ne 0 ]]; then
+		log_fail "Failed to compute checksum of '$dev'"
+		return 1
+	fi
+
+	echo "$checksum"
+	return 0
+}
+
+function test_shared_device
+{
+	typeset pool1="$1"
+	typeset pool2="$2"
+	typeset sharedvdev="$3"
+	typeset importflags="${4:-}"
+
+	log_note "$0: pool1 '$pool1', pool2 '$pool2' takes $sharedvdev."
+
+	log_must zpool create -o cachefile=$CPATH $TESTPOOL1 $pool1
+
+	log_must cp $CPATH $CPATHBKP
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool create -f $TESTPOOL2 $pool2
+
+	log_must zpool export $TESTPOOL2
+
+	typeset checksum1=$(dev_checksum $sharedvdev)
+
+	log_must zpool import -c $CPATHBKP $importflags $TESTPOOL1
+
+	log_must write_some_data $TESTPOOL1 2
+
+	log_must zpool destroy $TESTPOOL1
+
+	typeset checksum2=$(dev_checksum $sharedvdev)
+
+	if [[ $checksum1 == $checksum2 ]]; then
+		log_pos "Device hasn't been modified by original pool"
+	else
+		log_fail "Device has been modified by original pool." \
+		    "Checksum mismatch: $checksum1 != $checksum2."
+	fi
+
+	# Cleanup
+	log_must zpool import -d $DEVICE_DIR $TESTPOOL2
+	log_must zpool destroy $TESTPOOL2
+	log_must rm -f $CPATH $CPATHBKP
+
+	log_note ""
+}
+
+test_shared_device "mirror $VDEV0 $VDEV1" "mirror $VDEV1 $VDEV2" "$VDEV1"
+test_shared_device "mirror $VDEV0 $VDEV1 $VDEV2" "mirror $VDEV2 $VDEV3" \
+    "$VDEV2"
+test_shared_device "raidz $VDEV0 $VDEV1 $VDEV2" "$VDEV2" "$VDEV2"
+test_shared_device "$VDEV0 log $VDEV1" "$VDEV2 log $VDEV1" "$VDEV1" "-m"
+
+log_pass "Pool doesn't write to a device it doesn't own anymore."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_devices_missing.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_devices_missing.ksh
new file mode 100755
index 000000000..74b736aef
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_devices_missing.ksh
@@ -0,0 +1,122 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should be importable when up to 2 top-level devices are missing.
+#
+# STRATEGY:
+#	1. Create a pool.
+#	2. Write some data to the pool and checksum it.
+#	3. Add one or more devices.
+#	4. Write more data to the pool and checksum it.
+#	5. Export the pool.
+#	6. Move added devices out of the devices directory.
+#	7. Import the pool with missing devices.
+#	8. Verify that the first batch of data is intact.
+#	9. Verify that accessing the second batch of data doesn't suspend pool.
+#	10. Export the pool, move back missing devices, Re-import the pool.
+#	11. Verify that all the data is intact.
+#
+
+verify_runnable "global"
+
+function custom_cleanup
+{
+	log_must set_spa_load_verify_metadata 1
+	log_must set_spa_load_verify_data 1
+	log_must set_zfs_max_missing_tvds 0
+	log_must rm -rf $BACKUP_DEVICE_DIR
+	# Highly damaged pools may fail to be destroyed, so we export them.
+	poolexists $TESTPOOL1 && log_must zpool export $TESTPOOL1
+	cleanup
+}
+
+log_onexit custom_cleanup
+
+function test_devices_missing
+{
+	typeset poolcreate="$1"
+	typeset addvdevs="$2"
+	typeset missingvdevs="$3"
+	typeset -i missingtvds="$4"
+
+	log_note "$0: pool '$poolcreate', adding $addvdevs, then" \
+	    "moving away $missingvdevs."
+
+	log_must zpool create $TESTPOOL1 $poolcreate
+
+	log_must generate_data $TESTPOOL1 $MD5FILE "first"
+
+	log_must zpool add $TESTPOOL1 $addvdevs
+
+	log_must generate_data $TESTPOOL1 $MD5FILE2 "second"
+
+	log_must zpool export $TESTPOOL1
+
+	log_must mv $missingvdevs $BACKUP_DEVICE_DIR
+
+	# Tell zfs that it is ok to import a pool with missing top-level vdevs
+	log_must set_zfs_max_missing_tvds $missingtvds
+	# Missing devices means that data or metadata may be corrupted.
+	(( missingtvds > 1 )) && log_must set_spa_load_verify_metadata 0
+	log_must set_spa_load_verify_data 0
+	log_must zpool import -o readonly=on -d $DEVICE_DIR $TESTPOOL1
+
+	log_must verify_data_md5sums $MD5FILE
+
+	log_note "Try reading second batch of data, make sure pool doesn't" \
+	    "get suspended."
+	verify_data_md5sums $MD5FILE >/dev/null 2>&1
+
+	log_must zpool export $TESTPOOL1
+
+	typeset newpaths=$(echo "$missingvdevs" | \
+		sed "s:$DEVICE_DIR:$BACKUP_DEVICE_DIR:g")
+	log_must mv $newpaths $DEVICE_DIR
+	log_must set_spa_load_verify_metadata 1
+	log_must set_spa_load_verify_data 1
+	log_must set_zfs_max_missing_tvds 0
+	log_must zpool import -d $DEVICE_DIR $TESTPOOL1
+
+	log_must verify_data_md5sums $MD5FILE
+	log_must verify_data_md5sums $MD5FILE2
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+
+	log_note ""
+}
+
+log_must mkdir -p $BACKUP_DEVICE_DIR
+
+test_devices_missing "$VDEV0" "$VDEV1" "$VDEV1" 1
+test_devices_missing "$VDEV0" "$VDEV1 $VDEV2" "$VDEV1" 1
+test_devices_missing "mirror $VDEV0 $VDEV1" "mirror $VDEV2 $VDEV3" \
+    "$VDEV2 $VDEV3" 1
+test_devices_missing "$VDEV0 log $VDEV1" "$VDEV2" "$VDEV2" 1
+
+#
+# Note that we are testing for 2 non-consecutive missing devices.
+# Missing consecutive devices results in missing metadata. Because of
+# Missing metadata can cause the root dataset to fail to mount.
+#
+test_devices_missing "$VDEV0" "$VDEV1 $VDEV2 $VDEV3" "$VDEV1 $VDEV3" 2
+
+log_pass "zpool import succeeded with missing devices."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_paths_changed.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_paths_changed.ksh
new file mode 100755
index 000000000..457eb6a14
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_paths_changed.ksh
@@ -0,0 +1,98 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	A pool should be importable even if device paths have changed.
+#
+# STRATEGY:
+#	1. Create a pool.
+#	2. Export the pool.
+#	3. Change the paths of some of the devices.
+#	4. Verify that we can import the pool in a healthy state.
+#
+
+verify_runnable "global"
+
+log_onexit cleanup
+
+function test_new_paths
+{
+	typeset poolcreate="$1"
+	typeset pathstochange="$2"
+
+	log_note "$0: pool '$poolcreate', changing paths of $pathstochange."
+
+	log_must zpool create $TESTPOOL1 $poolcreate
+
+	log_must zpool export $TESTPOOL1
+
+	for dev in $pathstochange; do
+		log_must mv $dev "${dev}_new"
+	done
+
+	log_must zpool import -d $DEVICE_DIR $TESTPOOL1
+	log_must check_pool_healthy $TESTPOOL1
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	for dev in $pathstochange; do
+		log_must mv "${dev}_new" $dev
+	done
+
+	log_note ""
+}
+
+function test_swap_paths
+{
+	typeset poolcreate="$1"
+	typeset pathtoswap1="$2"
+	typeset pathtoswap2="$3"
+
+	log_note "$0: pool '$poolcreate', swapping paths of $pathtoswap1" \
+	    "and $pathtoswap2."
+
+	log_must zpool create $TESTPOOL1 $poolcreate
+
+	log_must zpool export $TESTPOOL1
+
+	log_must mv $pathtoswap2 "$pathtoswap2.tmp"
+	log_must mv $pathtoswap1 "$pathtoswap2"
+	log_must mv "$pathtoswap2.tmp" $pathtoswap1
+
+	log_must zpool import -d $DEVICE_DIR $TESTPOOL1
+	log_must check_pool_healthy $TESTPOOL1
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+
+	log_note ""
+}
+
+test_new_paths "$VDEV0 $VDEV1" "$VDEV0 $VDEV1"
+test_new_paths "mirror $VDEV0 $VDEV1" "$VDEV0 $VDEV1"
+test_new_paths "$VDEV0 log $VDEV1" "$VDEV1"
+test_new_paths "raidz $VDEV0 $VDEV1 $VDEV2" "$VDEV1"
+
+test_swap_paths "$VDEV0 $VDEV1" "$VDEV0" "$VDEV1"
+test_swap_paths "raidz $VDEV0 $VDEV1 $VDEV2" "$VDEV0" "$VDEV1"
+test_swap_paths "mirror $VDEV0 $VDEV1 mirror $VDEV2 $VDEV3" \
+    "$VDEV0" "$VDEV2"
+
+log_pass "zpool import succeeded after changing device paths."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_rewind_config_changed.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_rewind_config_changed.ksh
new file mode 100755
index 000000000..92d814015
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_rewind_config_changed.ksh
@@ -0,0 +1,239 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	It should be possible to rewind a pool beyond a configuration change.
+#
+# STRATEGY:
+#	1. Create a pool.
+#	2. Generate files and remember their md5sum.
+#	3. Note last synced txg.
+#	4. Take a snapshot to make sure old blocks are not overwritten.
+#	5. Perform zpool add/attach/detach/remove operation.
+#	6. Change device paths if requested and re-import pool.
+#	7. Overwrite the files.
+#	8. Export the pool.
+#	9. Verify that we can rewind the pool to the noted txg.
+#	10. Verify that the files are readable and retain their old data.
+#
+# DISCLAIMER:
+#	This test can fail since nothing guarantees that old MOS blocks aren't
+#	overwritten. Snapshots protect datasets and data files but not the MOS.
+#	sync_some_data_a_few_times interleaves file data and MOS data for a few
+#	txgs, thus increasing the odds that some txgs will have their MOS data
+#	left untouched.
+#
+
+verify_runnable "global"
+
+function custom_cleanup
+{
+	set_vdev_validate_skip 0
+	cleanup
+}
+
+log_onexit custom_cleanup
+
+function test_common
+{
+	typeset poolcreate="$1"
+	typeset addvdevs="$2"
+	typeset attachargs="${3:-}"
+	typeset detachvdev="${4:-}"
+	typeset removevdev="${5:-}"
+	typeset finalpool="${6:-}"
+
+	typeset poolcheck="$poolcreate"
+
+	log_must zpool create $TESTPOOL1 $poolcreate
+
+	log_must generate_data $TESTPOOL1 $MD5FILE
+
+	# syncing a few times while writing new data increases the odds that MOS
+	# metadata for some of the txgs will survive
+	log_must sync_some_data_a_few_times $TESTPOOL1
+	typeset txg
+	txg=$(get_last_txg_synced $TESTPOOL1)
+	log_must zfs snapshot -r $TESTPOOL1@snap1
+
+	#
+	# Perform config change operations
+	#
+	if [[ -n $addvdev ]]; then
+		log_must zpool add -f $TESTPOOL1 $addvdev
+	fi
+	if [[ -n $attachargs ]]; then
+		log_must zpool attach $TESTPOOL1 $attachargs
+	fi
+	if [[ -n $detachvdev ]]; then
+		log_must zpool detach $TESTPOOL1 $detachvdev
+	fi
+	if [[ -n $removevdev ]]; then
+		[[ -z $finalpool ]] &&
+		    log_fail "Must provide final pool status!"
+		log_must zpool remove $TESTPOOL1 $removevdev
+		log_must wait_for_pool_config $TESTPOOL1 "$finalpool"
+	fi
+	if [[ -n $pathstochange ]]; then
+		#
+		# Change device paths and re-import pool to update labels
+		#
+		zpool export $TESTPOOL1
+		for dev in $pathstochange; do
+			log_must mv $dev "${dev}_new"
+			poolcheck=$(echo "$poolcheck" | \
+			    sed "s:$dev:${dev}_new:g")
+		done
+		zpool import -d $DEVICE_DIR $TESTPOOL1
+	fi
+
+	log_must overwrite_data $TESTPOOL1 ""
+
+	log_must zpool export $TESTPOOL1
+
+	log_must zpool import -d $DEVICE_DIR -T $txg $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolcheck"
+
+	log_must verify_data_md5sums $MD5FILE
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	if [[ -n $pathstochange ]]; then
+		for dev in $pathstochange; do
+			log_must mv "${dev}_new" $dev
+		done
+	fi
+	# Fast way to clear vdev labels
+	log_must zpool create -f $TESTPOOL2 $VDEV0 $VDEV1 $VDEV2 $VDEV3 $VDEV4
+	log_must zpool destroy $TESTPOOL2
+
+	log_note ""
+}
+
+function test_add_vdevs
+{
+	typeset poolcreate="$1"
+	typeset addvdevs="$2"
+
+	log_note "$0: pool '$poolcreate', add $addvdevs."
+
+	test_common "$poolcreate" "$addvdevs"
+}
+
+function test_attach_vdev
+{
+	typeset poolcreate="$1"
+	typeset attachto="$2"
+	typeset attachvdev="$3"
+
+	log_note "$0: pool '$poolcreate', attach $attachvdev to $attachto."
+
+	test_common "$poolcreate" "" "$attachto $attachvdev"
+}
+
+function test_detach_vdev
+{
+	typeset poolcreate="$1"
+	typeset detachvdev="$2"
+
+	log_note "$0: pool '$poolcreate', detach $detachvdev."
+
+	test_common "$poolcreate" "" "" "$detachvdev"
+}
+
+function test_attach_detach_vdev
+{
+	typeset poolcreate="$1"
+	typeset attachto="$2"
+	typeset attachvdev="$3"
+	typeset detachvdev="$4"
+
+	log_note "$0: pool '$poolcreate', attach $attachvdev to $attachto," \
+	    "then detach $detachvdev."
+
+	test_common "$poolcreate" "" "$attachto $attachvdev" "$detachvdev"
+}
+
+function test_remove_vdev
+{
+	typeset poolcreate="$1"
+	typeset removevdev="$2"
+	typeset finalpool="$3"
+
+	log_note "$0: pool '$poolcreate', remove $removevdev."
+
+	test_common "$poolcreate" "" "" "" "$removevdev" "$finalpool"
+}
+
+# Record txg history
+is_linux && log_must set_tunable32 zfs_txg_history 100
+
+# Make the devices bigger to reduce chances of overwriting MOS metadata.
+increase_device_sizes $(( FILE_SIZE * 4 ))
+
+# Part of the rewind test is to see how it reacts to path changes
+typeset pathstochange="$VDEV0 $VDEV1 $VDEV2 $VDEV3"
+
+log_note " == test rewind after device addition == "
+
+test_add_vdevs "$VDEV0" "$VDEV1"
+test_add_vdevs "$VDEV0 $VDEV1" "$VDEV2"
+test_add_vdevs "$VDEV0" "$VDEV1 $VDEV2"
+test_add_vdevs "mirror $VDEV0 $VDEV1" "mirror $VDEV2 $VDEV3"
+test_add_vdevs "$VDEV0" "raidz $VDEV1 $VDEV2 $VDEV3"
+test_add_vdevs "$VDEV0" "log $VDEV1"
+test_add_vdevs "$VDEV0 log $VDEV1" "$VDEV2"
+
+log_note " == test rewind after device attach == "
+
+test_attach_vdev "$VDEV0" "$VDEV0" "$VDEV1"
+test_attach_vdev "mirror $VDEV0 $VDEV1" "$VDEV0" "$VDEV2"
+test_attach_vdev "$VDEV0 $VDEV1" "$VDEV0" "$VDEV2"
+
+log_note " == test rewind after device removal == "
+
+# Once we remove a device it will be overlooked in the device scan, so we must
+# preserve its original path
+pathstochange="$VDEV0 $VDEV2"
+test_remove_vdev "$VDEV0 $VDEV1 $VDEV2" "$VDEV1" "$VDEV0 $VDEV2"
+
+#
+# Path change and detach are incompatible. Detach changes the guid of the vdev
+# so we have no direct way to link the new path to an existing vdev.
+#
+pathstochange=""
+
+log_note " == test rewind after device detach == "
+
+test_detach_vdev "mirror $VDEV0 $VDEV1" "$VDEV1"
+test_detach_vdev "mirror $VDEV0 $VDEV1 mirror $VDEV2 $VDEV3" "$VDEV1"
+test_detach_vdev "$VDEV0 log mirror $VDEV1 $VDEV2" "$VDEV2"
+
+log_note " == test rewind after device attach followed by device detach == "
+
+#
+# We need to disable vdev validation since once we detach VDEV1, VDEV0 will
+# inherit the mirror tvd's guid and lose its original guid.
+#
+set_vdev_validate_skip 1
+test_attach_detach_vdev "$VDEV0" "$VDEV0" "$VDEV1" "$VDEV1"
+set_vdev_validate_skip 0
+
+log_pass "zpool import rewind after configuration change passed."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_rewind_device_replaced.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_rewind_device_replaced.ksh
new file mode 100755
index 000000000..5ff1c47f3
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/import_rewind_device_replaced.ksh
@@ -0,0 +1,186 @@
+#!/usr/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.kshlib
+
+#
+# DESCRIPTION:
+#	It should be possible to rewind a pool beyond a device replacement.
+#
+# STRATEGY:
+#	1. Create a pool.
+#	2. Generate files and remember their md5sum.
+#	3. Sync a few times and note last synced txg.
+#	4. Take a snapshot to make sure old blocks are not overwritten.
+#	5. Initiate device replacement and export the pool. Special care must
+#	   be taken so that resilvering doesn't complete before the export.
+#	6. Test 1: Rewind pool to noted txg and then verify data checksums.
+#	   Import it read-only so that we do not overwrite blocks in later txgs.
+#	7. Re-import pool at latest txg and let the replacement finish.
+#	8. Export the pool an remove the new device - we shouldn't need it.
+#	9. Test 2: Rewind pool to noted txg and then verify data checksums.
+#
+# STRATEGY TO SLOW DOWN RESILVERING:
+#	1. Reduce zfs_txg_timeout, which controls how long can we resilver for
+#	   each sync.
+#	2. Add data to pool
+#	3. Re-import the pool so that data isn't cached
+#	4. Use zinject to slow down device I/O
+#	5. Trigger the resilvering
+#	6. Use spa freeze to stop writing to the pool.
+#	7. Clear zinject events (needed to export the pool)
+#	8. Export the pool
+#
+# DISCLAIMER:
+#	This test can fail since nothing guarantees that old MOS blocks aren't
+#	overwritten. Snapshots protect datasets and data files but not the MOS.
+#	sync_some_data_a_few_times interleaves file data and MOS data for a few
+#	txgs, thus increasing the odds that some txgs will have their MOS data
+#	left untouched.
+#
+
+verify_runnable "global"
+
+ZFS_TXG_TIMEOUT=""
+
+function custom_cleanup
+{
+	# Revert zfs_txg_timeout to defaults
+	[[ -n ZFS_TXG_TIMEOUT ]] &&
+	    log_must set_zfs_txg_timeout $ZFS_TXG_TIMEOUT
+	log_must rm -rf $BACKUP_DEVICE_DIR
+	zinject -c all
+	cleanup
+}
+
+log_onexit custom_cleanup
+
+function test_replace_vdev
+{
+	typeset poolcreate="$1"
+	typeset replacevdev="$2"
+	typeset replaceby="$3"
+	typeset poolfinalstate="$4"
+	typeset zinjectdevices="$5"
+	typeset writedata="$6"
+
+	log_note "$0: pool '$poolcreate', replace $replacevdev by $replaceby."
+
+	log_must zpool create $TESTPOOL1 $poolcreate
+
+	# generate data and checksum it
+	log_must generate_data $TESTPOOL1 $MD5FILE
+
+	# add more data so that resilver takes longer
+	log_must write_some_data $TESTPOOL1 $writedata
+
+	# Syncing a few times while writing new data increases the odds that
+	# MOS metadata for some of the txgs will survive.
+	log_must sync_some_data_a_few_times $TESTPOOL1
+	typeset txg
+	txg=$(get_last_txg_synced $TESTPOOL1)
+	log_must zfs snapshot -r $TESTPOOL1@snap1
+
+	# This should not free original data.
+	log_must overwrite_data $TESTPOOL1 ""
+
+	# Steps to insure resilvering happens very slowly.
+	log_must zpool export $TESTPOOL1
+	log_must zpool import -d $DEVICE_DIR $TESTPOOL1
+	typeset device
+	for device in $zinjectdevices ; do
+		log_must zinject -d $device -D 200:1 $TESTPOOL1 > /dev/null
+	done
+	log_must zpool replace $TESTPOOL1 $replacevdev $replaceby
+
+	# We must disable zinject in order to export the pool, so we freeze
+	# it first to prevent writing out subsequent resilvering progress.
+	log_must zpool freeze $TESTPOOL1
+	# Confirm pool is still replacing
+	log_must pool_is_replacing $TESTPOOL1
+	log_must zinject -c all > /dev/null
+	log_must zpool export $TESTPOOL1
+
+	############################################################
+	# Test 1: rewind while device is resilvering.
+	# Import read only to avoid overwriting more recent blocks.
+	############################################################
+	log_must zpool import -d $DEVICE_DIR -o readonly=on -T $txg $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolcreate"
+
+	log_must verify_data_md5sums $MD5FILE
+
+	log_must zpool export $TESTPOOL1
+
+	# Import pool at latest txg to finish the resilvering
+	log_must zpool import -d $DEVICE_DIR $TESTPOOL1
+	log_must overwrite_data $TESTPOOL1 ""
+	log_must wait_for_pool_config $TESTPOOL1 "$poolfinalstate"
+	log_must zpool export $TESTPOOL1
+
+	# Move out the new device
+	log_must mv $replaceby $BACKUP_DEVICE_DIR/
+
+	############################################################
+	# Test 2: rewind after device has been replaced.
+	# Import read-write since we won't need the pool anymore.
+	############################################################
+	log_must zpool import -d $DEVICE_DIR -T $txg $TESTPOOL1
+	log_must check_pool_config $TESTPOOL1 "$poolcreate"
+
+	log_must verify_data_md5sums $MD5FILE
+
+	# Cleanup
+	log_must zpool destroy $TESTPOOL1
+	# Restore the device we moved out
+	log_must mv "$BACKUP_DEVICE_DIR/$(basename $replaceby)" $DEVICE_DIR/
+	# Fast way to clear vdev labels
+	log_must zpool create -f $TESTPOOL2 $VDEV0 $VDEV1 $VDEV2 $VDEV3 $VDEV4
+	log_must zpool destroy $TESTPOOL2
+
+	log_note ""
+}
+
+# Record txg history
+is_linux && log_must set_tunable32 zfs_txg_history 100
+
+log_must mkdir -p $BACKUP_DEVICE_DIR
+# Make the devices bigger to reduce chances of overwriting MOS metadata.
+increase_device_sizes $(( FILE_SIZE * 4 ))
+
+# We set zfs_txg_timeout to 1 to reduce resilvering time at each sync.
+ZFS_TXG_TIMEOUT=$(get_zfs_txg_timeout)
+set_zfs_txg_timeout 1
+
+test_replace_vdev "$VDEV0 $VDEV1" \
+    "$VDEV1" "$VDEV2" \
+    "$VDEV0 $VDEV2" \
+    "$VDEV0 $VDEV1" 15
+
+test_replace_vdev "mirror $VDEV0 $VDEV1" \
+	"$VDEV1" "$VDEV2" \
+	"mirror $VDEV0 $VDEV2" \
+	"$VDEV0 $VDEV1" 10
+
+test_replace_vdev "raidz $VDEV0 $VDEV1 $VDEV2" \
+	"$VDEV1" "$VDEV3" \
+	"raidz $VDEV0 $VDEV3 $VDEV2" \
+	"$VDEV0 $VDEV1 $VDEV2" 10
+
+set_zfs_txg_timeout $ZFS_TXG_TIMEOUT
+
+log_pass "zpool import rewind after device replacement passed."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/setup.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_import/setup.ksh
index 142771de6..d81e66636 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_import/setup.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/setup.ksh
@@ -69,26 +69,14 @@ log_must zfs create $TESTPOOL/$TESTFS
 log_must zfs set mountpoint=$TESTDIR $TESTPOOL/$TESTFS
 
 DISK2="$(echo $DISKS | nawk '{print $2}')"
-if is_mpath_device $DISK2; then
-	echo "y" | newfs -v $DEV_DSKDIR/$DISK2 >/dev/null 2>&1
-	(( $? != 0 )) &&
-		log_untested "Unable to setup a $NEWFS_DEFAULT_FS file system"
+echo "y" | newfs -v $DEV_DSKDIR/$DISK2 >/dev/null 2>&1
+(( $? != 0 )) &&
+	log_untested "Unable to setup a $NEWFS_DEFAULT_FS file system"
 
-	[[ ! -d $DEVICE_DIR ]] && \
-		log_must mkdir -p $DEVICE_DIR
+[[ ! -d $DEVICE_DIR ]] && \
+	log_must mkdir -p $DEVICE_DIR
 
-	log_must mount $DEV_DSKDIR/$DISK2 $DEVICE_DIR
-else
-	log_must set_partition 0 "" $FS_SIZE $ZFS_DISK2
-	echo "y" | newfs -v $DEV_DSKDIR/$ZFSSIDE_DISK2 >/dev/null 2>&1
-	(( $? != 0 )) &&
-		log_untested "Unable to setup a $NEWFS_DEFAULT_FS file system"
-
-	[[ ! -d $DEVICE_DIR ]] && \
-		log_must mkdir -p $DEVICE_DIR
-
-	log_must mount $DEV_DSKDIR/$ZFSSIDE_DISK2 $DEVICE_DIR
-fi
+log_must mount $DEV_DSKDIR/$DISK2 $DEVICE_DIR
 
 i=0
 while (( i < $MAX_NUM )); do
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import.cfg b/tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import.cfg
index 648f82c2b..20f43cefa 100644
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import.cfg
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import.cfg
@@ -25,7 +25,7 @@
 #
 
 #
-# Copyright (c) 2012, 2015 by Delphix. All rights reserved.
+# Copyright (c) 2012, 2016 by Delphix. All rights reserved.
 #
 
 . $STF_SUITE/include/libtest.shlib
@@ -57,10 +57,8 @@ case "${#disk_array[*]}" in
 		if ( is_mpath_device $ZFS_DISK1 ) && [[ -z $(echo $ZFS_DISK1 | awk 'substr($1,18,1)\
                     ~ /^[[:digit:]]+$/') ]] || ( is_real_device $ZFS_DISK1 ); then
 			ZFSSIDE_DISK1=${ZFS_DISK1}1
-			ZFSSIDE_DISK2=${ZFS_DISK2}2
 		elif ( is_mpath_device $ZFS_DISK1 || is_loop_device $ZFS_DISK1 ); then
 			ZFSSIDE_DISK1=${ZFS_DISK1}p1
-			ZFSSIDE_DISK2=${ZFS_DISK2}p2
 		else
 			log_fail "$ZFS_DISK1 not supported for partitioning."
 		fi
@@ -71,7 +69,6 @@ case "${#disk_array[*]}" in
 		ZFS_DISK1=${disk_array[0]}
 		ZFSSIDE_DISK1=${ZFS_DISK1}s0
 		ZFS_DISK2=${disk_array[0]}
-		ZFSSIDE_DISK2=${ZFS_DISK2}s1
 	fi
 	;;
 *)
@@ -96,14 +93,6 @@ case "${#disk_array[*]}" in
 			log_fail "$ZFS_DISK1 not supported for partitioning."
 		fi
 		ZFS_DISK2=${disk_array[1]}
-		if ( is_mpath_device $ZFS_DISK2 ) && [[ -z $(echo $ZFS_DISK2 | awk 'substr($1,18,1)\
-		    ~ /^[[:digit:]]+$/') ]] || ( is_real_device $ZFS_DISK2 ); then
-			ZFSSIDE_DISK2=${ZFS_DISK2}1
-		elif ( is_mpath_device $ZFS_DISK2 || is_loop_device $ZFS_DISK2 ); then
-			ZFSSIDE_DISK2=${ZFS_DISK2}p1
-		else
-			log_fail "$ZFS_DISK2 not supported for partitioning."
-		fi
 	else
 		export DEV_DSKDIR="/dev"
 		PRIMARY_SLICE=2
@@ -111,15 +100,14 @@ case "${#disk_array[*]}" in
 		ZFS_DISK1=${disk_array[0]}
 		ZFSSIDE_DISK1=${ZFS_DISK1}s0
 		ZFS_DISK2=${disk_array[1]}
-		ZFSSIDE_DISK2=${ZFS_DISK2}s0
 	fi
 	;;
 esac
 
-export DISK_COUNT ZFS_DISK1 ZFSSIDE_DISK1 ZFS_DISK2 ZFSSIDE_DISK2
+export DISK_COUNT ZFS_DISK1 ZFSSIDE_DISK1 ZFS_DISK2
 
-export FS_SIZE="$((($MINVDEVSIZE / (1024 * 1024)) * 16))m"
-export FILE_SIZE="$(($MINVDEVSIZE / 2))"
+export FS_SIZE="$((($MINVDEVSIZE / (1024 * 1024)) * 32))m"
+export FILE_SIZE="$((MINVDEVSIZE))"
 export SLICE_SIZE="$((($MINVDEVSIZE / (1024 * 1024)) * 2))m"
 export MAX_NUM=5
 export GROUP_NUM=3
@@ -129,6 +117,12 @@ export DEVICE_FILE=disk
 export DEVICE_ARCHIVE=archive_import-test
 export MYTESTFILE=$STF_SUITE/include/libtest.shlib
 
+export CPATH=/var/tmp/cachefile.$$
+export CPATHBKP=/var/tmp/cachefile.$$.bkp
+export CPATHBKP2=/var/tmp/cachefile.$$.bkp2
+export MD5FILE=/var/tmp/md5sums.$$
+export MD5FILE2=/var/tmp/md5sums.$$.2
+
 typeset -i num=0
 while (( num < $GROUP_NUM )); do
 	DEVICE_FILES="$DEVICE_FILES ${DEVICE_DIR}/${DEVICE_FILE}$num"
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import.kshlib b/tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import.kshlib
new file mode 100644
index 000000000..bc89d8159
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import.kshlib
@@ -0,0 +1,376 @@
+#!/usr/bin/ksh
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2016 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/cli_root/zpool_import/zpool_import.cfg
+
+#
+# Prototype cleanup function for zpool_import tests.
+#
+function cleanup
+{
+	destroy_pool $TESTPOOL1
+
+	log_must rm -f $CPATH $CPATHBKP $CPATHBKP2 $MD5FILE $MD5FILE2
+
+	log_must rm -rf $DEVICE_DIR/*
+	typeset i=0
+	while (( i < $MAX_NUM )); do
+		log_must mkfile $FILE_SIZE ${DEVICE_DIR}/${DEVICE_FILE}$i
+		((i += 1))
+	done
+	is_linux && set_tunable32 "zfs_txg_history" 0
+}
+
+#
+# Write a bit of data and sync several times.
+# This function is intended to be used by zpool rewind tests.
+#
+function sync_some_data_a_few_times
+{
+	typeset pool=$1
+	typeset -i a_few_times=${2:-10}
+
+	typeset file="/$pool/tmpfile"
+	for i in {0..$a_few_times}; do
+		dd if=/dev/urandom of=${file}_$i bs=128k count=10
+		sync_pool "$pool"
+	done
+
+	return 0
+}
+
+#
+# Just write a moderate amount of data to the pool.
+#
+function write_some_data
+{
+	typeset pool=$1
+	typeset files10mb=${2:-10}
+
+	typeset ds="$pool/fillerds"
+	zfs create $ds
+	[[ $? -ne 0 ]] && return 1
+
+	# Create 100 MB of data
+	typeset file="/$ds/fillerfile"
+	for i in {1..$files10mb}; do
+		dd if=/dev/urandom of=$file.$i bs=128k count=80
+		[[ $? -ne 0 ]] && return 1
+	done
+
+	return 0
+}
+
+#
+# Create/overwrite a few datasets with files.
+# Apply md5sum on all the files and store checksums in a file.
+#
+# newdata: overwrite existing files if false.
+# md5file: file where to store md5sums
+# datasetname: base name for datasets
+#
+function _generate_data_common
+{
+	typeset pool=$1
+	typeset newdata=$2
+	typeset md5file=$3
+	typeset datasetname=$4
+
+	typeset -i datasets=3
+	typeset -i files=5
+	typeset -i blocks=10
+
+	[[ -n $md5file ]] && rm -f $md5file
+	for i in {1..$datasets}; do
+		( $newdata ) && log_must zfs create "$pool/$datasetname$i"
+		for j in {1..$files}; do
+			typeset file="/$pool/$datasetname$i/file$j"
+			dd if=/dev/urandom of=$file bs=128k count=$blocks > /dev/null
+			[[ -n $md5file ]] && md5sum $file >> $md5file
+		done
+		( $newdata ) && sync_pool "$pool"
+	done
+
+	return 0
+}
+
+function generate_data
+{
+	typeset pool=$1
+	typeset md5file="$2"
+	typeset datasetname=${3:-ds}
+
+	_generate_data_common $pool true "$md5file" $datasetname
+}
+
+function overwrite_data
+{
+	typeset pool=$1
+	typeset md5file="$2"
+	typeset datasetname=${3:-ds}
+
+	_generate_data_common $1 false "$md5file" $datasetname
+}
+
+#
+# Verify md5sums of every file in md5sum file $1.
+#
+function verify_data_md5sums
+{
+	typeset md5file=$1
+
+	if [[ ! -f $md5file ]]; then
+		log_note "md5 sums file '$md5file' doesn't exist"
+		return 1
+	fi
+
+	md5sum -c --quiet $md5file
+	return $?
+}
+
+#
+# Set devices size in DEVICE_DIR to $1.
+#
+function increase_device_sizes
+{
+	typeset newfilesize=$1
+
+	typeset -i i=0
+	while (( i < $MAX_NUM )); do
+		log_must mkfile $newfilesize ${DEVICE_DIR}/${DEVICE_FILE}$i
+		((i += 1))
+	done
+}
+
+#
+# Translate vdev names returned by zpool status into more generic names.
+#
+# eg: mirror-2 --> mirror
+#
+function _translate_vdev
+{
+	typeset vdev=$1
+
+	typeset keywords="mirror replacing raidz1 raidz2 raidz3 indirect"
+	for word in $keywords; do
+		echo $vdev | egrep "^${word}-[0-9]+\$" > /dev/null
+		if [[ $? -eq 0 ]]; then
+			vdev=$word
+			break
+		fi
+	done
+
+	[[ $vdev == "logs" ]] && echo "log" && return 0
+	[[ $vdev == "raidz1" ]] && echo "raidz" && return 0
+
+	echo $vdev
+	return 0
+}
+
+#
+# Check that pool configuration returned by zpool status matches expected
+# configuration. Format for the check string is same as the vdev arguments for
+# creating a pool
+# Add -q for quiet mode.
+#
+# eg: check_pool_config pool1 "mirror c0t0d0s0 c0t1d0s0 log c1t1d0s0"
+#
+function check_pool_config
+{
+	typeset logfailure=true
+	if [[ $1 == '-q' ]]; then
+		logfailure=false
+		shift
+	fi
+
+	typeset poolname=$1
+	typeset expected=$2
+
+	typeset status
+	status=$(zpool status $poolname 2>&1)
+	if [[ $? -ne 0 ]]; then
+		if ( $logfailure ); then
+			log_note "zpool status $poolname failed: $status"
+		fi
+		return 1
+	fi
+
+	typeset actual=""
+	typeset began=false
+	printf "$status\n" | while read line; do
+		typeset vdev=$(echo "$line" | awk '{printf $1}')
+		if ( ! $began ) && [[ $vdev == NAME ]]; then
+			began=true
+			continue
+		fi
+		( $began ) && [[ -z $vdev ]] && break;
+
+		if ( $began ); then
+			[[ -z $actual ]] && actual="$vdev" && continue
+			vdev=$(_translate_vdev $vdev)
+			actual="$actual $vdev"
+		fi
+	done
+
+	expected="$poolname $expected"
+
+	if [[ "$actual" != "$expected" ]]; then
+		if ( $logfailure ); then
+			log_note "expected pool vdevs:"
+			log_note "> '$expected'"
+			log_note "actual pool vdevs:"
+			log_note "> '$actual'"
+		fi
+		return 1
+	fi
+
+	return 0
+}
+
+#
+# Check that pool configuration returned by zpool status matches expected
+# configuration within a given timeout in seconds. See check_pool_config().
+#
+# eg: wait_for_pool_config pool1 "mirror c0t0d0s0 c0t1d0s0" 60
+#
+function wait_for_pool_config
+{
+	typeset poolname=$1
+	typeset expectedconfig="$2"
+	typeset -i timeout=${3:-60}
+
+	timeout=$(( $timeout + $(date +%s) ))
+
+	while  (( $(date +%s) < $timeout )); do
+		check_pool_config -q $poolname "$expectedconfig"
+		[[ $? -eq 0 ]] && return 0
+		sleep 3
+	done
+
+	check_pool_config $poolname "$expectedconfig"
+	return $?
+}
+
+#
+# Check that pool status is ONLINE
+#
+function check_pool_healthy
+{
+	typeset pool=$1
+
+	typeset status
+	status=$(zpool status $pool 2>&1)
+	if [[ $? -ne 0 ]]; then
+		log_note "zpool status $pool failed: $status"
+		return 1
+	fi
+
+	status=$(echo "$status" | grep "$pool" | grep -v "pool:" | \
+	    awk '{print $2}')
+
+	if [[ $status != "ONLINE" ]]; then
+		log_note "Invalid zpool status for '$pool': '$status'" \
+		    "!= 'ONLINE'"
+		return 1
+	fi
+
+	return 0
+}
+
+#
+# Return 0 if a device is currently being replaced in the pool.
+#
+function pool_is_replacing
+{
+	typeset pool=$1
+
+	zpool status $pool | grep "replacing" | grep "ONLINE" > /dev/null
+
+	return $?
+}
+
+function set_vdev_validate_skip
+{
+	set_tunable32 "vdev_validate_skip" "$1"
+}
+
+function get_zfs_txg_timeout
+{
+	get_tunable "zfs_txg_timeout"
+}
+
+function set_zfs_txg_timeout
+{
+	set_tunable32 "zfs_txg_timeout" "$1"
+}
+
+function set_spa_load_verify_metadata
+{
+	set_tunable32 "spa_load_verify_metadata" "$1"
+}
+
+function set_spa_load_verify_data
+{
+	set_tunable32 "spa_load_verify_data" "$1"
+}
+
+function set_zfs_max_missing_tvds
+{
+	set_tunable32 "zfs_max_missing_tvds" "$1"
+}
+
+#
+# Use mdb to find the last txg that was synced in an active pool.
+#
+function get_last_txg_synced
+{
+	typeset pool=$1
+
+	if is_linux; then
+		txg=$(tail "/proc/spl/kstat/zfs/$pool/txgs" |
+		    awk '$3=="C" {print $1}' | tail -1)
+		[[ "$txg" ]] || txg=0
+		echo $txg
+		return 0
+	fi
+
+	typeset spas
+	spas=$(mdb -k -e "::spa")
+	[[ $? -ne 0 ]] && return 1
+
+	typeset spa=""
+	print "$spas\n" | while read line; do
+		typeset poolname=$(echo "$line" | awk '{print $3}')
+		typeset addr=$(echo "$line" | awk '{print $1}')
+		if [[ $poolname == $pool ]]; then
+			spa=$addr
+			break
+		fi
+	done
+	if [[ -z $spa ]]; then
+		log_fail "Couldn't find pool '$pool'"
+		return 1
+	fi
+	typeset mdbcmd="$spa::print spa_t spa_ubsync.ub_txg | ::eval '.=E'"
+	typeset -i txg
+	txg=$(mdb -k -e "$mdbcmd")
+	[[ $? -ne 0 ]] && return 1
+
+	echo $txg
+	return 0
+}