OpenZFS 7614, 9064 - zfs device evacuation/removal

OpenZFS 7614 - zfs device evacuation/removal
OpenZFS 9064 - remove_mirror should wait for device removal to complete

This project allows top-level vdevs to be removed from the storage pool
with "zpool remove", reducing the total amount of storage in the pool.
This operation copies all allocated regions of the device to be removed
onto other devices, recording the mapping from old to new location.
After the removal is complete, read and free operations to the removed
(now "indirect") vdev must be remapped and performed at the new location
on disk.  The indirect mapping table is kept in memory whenever the pool
is loaded, so there is minimal performance overhead when doing operations
on the indirect vdev.

The size of the in-memory mapping table will be reduced when its entries
become "obsolete" because they are no longer used by any block pointers
in the pool.  An entry becomes obsolete when all the blocks that use
it are freed.  An entry can also become obsolete when all the snapshots
that reference it are deleted, and the block pointers that reference it
have been "remapped" in all filesystems/zvols (and clones).  Whenever an
indirect block is written, all the block pointers in it will be "remapped"
to their new (concrete) locations if possible.  This process can be
accelerated by using the "zfs remap" command to proactively rewrite all
indirect blocks that reference indirect (removed) vdevs.

Note that when a device is removed, we do not verify the checksum of
the data that is copied.  This makes the process much faster, but if it
were used on redundant vdevs (i.e. mirror or raidz vdevs), it would be
possible to copy the wrong data, when we have the correct data on e.g.
the other side of the mirror.

At the moment, only mirrors and simple top-level vdevs can be removed
and no removal is allowed if any of the top-level vdevs are raidz.

Porting Notes:

* Avoid zero-sized kmem_alloc() in vdev_compact_children().

    The device evacuation code adds a dependency that
    vdev_compact_children() be able to properly empty the vdev_child
    array by setting it to NULL and zeroing vdev_children.  Under Linux,
    kmem_alloc() and related functions return a sentinel pointer rather
    than NULL for zero-sized allocations.

* Remove comment regarding "mpt" driver where zfs_remove_max_segment
  is initialized to SPA_MAXBLOCKSIZE.

  Change zfs_condense_indirect_commit_entry_delay_ticks to
  zfs_condense_indirect_commit_entry_delay_ms for consistency with
  most other tunables in which delays are specified in ms.

* ZTS changes:

    Use set_tunable rather than mdb
    Use zpool sync as appropriate
    Use sync_pool instead of sync
    Kill jobs during test_removal_with_operation to allow unmount/export
    Don't add non-disk names such as "mirror" or "raidz" to $DISKS
    Use $TEST_BASE_DIR instead of /tmp
    Increase HZ from 100 to 1000 which is more common on Linux

    removal_multiple_indirection.ksh
        Reduce iterations in order to not time out on the code
        coverage builders.

    removal_resume_export:
        Functionally, the test case is correct but there exists a race
        where the kernel thread hasn't been fully started yet and is
        not visible.  Wait for up to 1 second for the removal thread
        to be started before giving up on it.  Also, increase the
        amount of data copied in order that the removal not finish
        before the export has a chance to fail.

* MMP compatibility, the concept of concrete versus non-concrete devices
  has slightly changed the semantics of vdev_writeable().  Update
  mmp_random_leaf_impl() accordingly.

* Updated dbuf_remap() to handle the org.zfsonlinux:large_dnode pool
  feature which is not supported by OpenZFS.

* Added support for new vdev removal tracepoints.

* Test cases removal_with_zdb and removal_condense_export have been
  intentionally disabled.  When run manually they pass as intended,
  but when running in the automated test environment they produce
  unreliable results on the latest Fedora release.

  They may work better once the upstream pool import refectoring is
  merged into ZoL at which point they will be re-enabled.

Authored by: Matthew Ahrens <[email protected]>
Reviewed-by: Alex Reece <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Reviewed-by: John Kennedy <[email protected]>
Reviewed-by: Prakash Surya <[email protected]>
Reviewed by: Richard Laager <[email protected]>
Reviewed by: Tim Chase <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Approved by: Garrett D'Amore <[email protected]>
Ported-by: Tim Chase <[email protected]>
Signed-off-by: Tim Chase <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/7614
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/f539f1eb
Closes #6900

1 files changed, 1925 insertions, 0 deletions

diff --git a/module/zfs/vdev_removal.c b/module/zfs/vdev_removal.c
new file mode 100644
index 000000000..6e81bf014
--- /dev/null
+++ b/module/zfs/vdev_removal.c
@@ -0,0 +1,1925 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2017 by Delphix. All rights reserved.
+ */
+
+#include <sys/zfs_context.h>
+#include <sys/spa_impl.h>
+#include <sys/dmu.h>
+#include <sys/dmu_tx.h>
+#include <sys/zap.h>
+#include <sys/vdev_impl.h>
+#include <sys/metaslab.h>
+#include <sys/metaslab_impl.h>
+#include <sys/uberblock_impl.h>
+#include <sys/txg.h>
+#include <sys/avl.h>
+#include <sys/bpobj.h>
+#include <sys/dsl_pool.h>
+#include <sys/dsl_synctask.h>
+#include <sys/dsl_dir.h>
+#include <sys/arc.h>
+#include <sys/zfeature.h>
+#include <sys/vdev_indirect_births.h>
+#include <sys/vdev_indirect_mapping.h>
+#include <sys/abd.h>
+#include <sys/trace_vdev.h>
+
+/*
+ * This file contains the necessary logic to remove vdevs from a
+ * storage pool.  Currently, the only devices that can be removed
+ * are log, cache, and spare devices; and top level vdevs from a pool
+ * w/o raidz or mirrors.  (Note that members of a mirror can be removed
+ * by the detach operation.)
+ *
+ * Log vdevs are removed by evacuating them and then turning the vdev
+ * into a hole vdev while holding spa config locks.
+ *
+ * Top level vdevs are removed and converted into an indirect vdev via
+ * a multi-step process:
+ *
+ *  - Disable allocations from this device (spa_vdev_remove_top).
+ *
+ *  - From a new thread (spa_vdev_remove_thread), copy data from
+ *    the removing vdev to a different vdev.  The copy happens in open
+ *    context (spa_vdev_copy_impl) and issues a sync task
+ *    (vdev_mapping_sync) so the sync thread can update the partial
+ *    indirect mappings in core and on disk.
+ *
+ *  - If a free happens during a removal, it is freed from the
+ *    removing vdev, and if it has already been copied, from the new
+ *    location as well (free_from_removing_vdev).
+ *
+ *  - After the removal is completed, the copy thread converts the vdev
+ *    into an indirect vdev (vdev_remove_complete) before instructing
+ *    the sync thread to destroy the space maps and finish the removal
+ *    (spa_finish_removal).
+ */
+
+typedef struct vdev_copy_arg {
+	metaslab_t	*vca_msp;
+	uint64_t	vca_outstanding_bytes;
+	kcondvar_t	vca_cv;
+	kmutex_t	vca_lock;
+} vdev_copy_arg_t;
+
+typedef struct vdev_copy_seg_arg {
+	vdev_copy_arg_t	*vcsa_copy_arg;
+	uint64_t	vcsa_txg;
+	dva_t		*vcsa_dest_dva;
+	blkptr_t	*vcsa_dest_bp;
+} vdev_copy_seg_arg_t;
+
+/*
+ * The maximum amount of allowed data we're allowed to copy from a device
+ * at a time when removing it.
+ */
+int zfs_remove_max_copy_bytes = 8 * 1024 * 1024;
+
+/*
+ * The largest contiguous segment that we will attempt to allocate when
+ * removing a device.  This can be no larger than SPA_MAXBLOCKSIZE.  If
+ * there is a performance problem with attempting to allocate large blocks,
+ * consider decreasing this.
+ */
+int zfs_remove_max_segment = SPA_MAXBLOCKSIZE;
+
+#define	VDEV_REMOVAL_ZAP_OBJS	"lzap"
+
+static void spa_vdev_remove_thread(void *arg);
+
+static void
+spa_sync_removing_state(spa_t *spa, dmu_tx_t *tx)
+{
+	VERIFY0(zap_update(spa->spa_dsl_pool->dp_meta_objset,
+	    DMU_POOL_DIRECTORY_OBJECT,
+	    DMU_POOL_REMOVING, sizeof (uint64_t),
+	    sizeof (spa->spa_removing_phys) / sizeof (uint64_t),
+	    &spa->spa_removing_phys, tx));
+}
+
+static nvlist_t *
+spa_nvlist_lookup_by_guid(nvlist_t **nvpp, int count, uint64_t target_guid)
+{
+	for (int i = 0; i < count; i++) {
+		uint64_t guid =
+		    fnvlist_lookup_uint64(nvpp[i], ZPOOL_CONFIG_GUID);
+
+		if (guid == target_guid)
+			return (nvpp[i]);
+	}
+
+	return (NULL);
+}
+
+static void
+spa_vdev_remove_aux(nvlist_t *config, char *name, nvlist_t **dev, int count,
+    nvlist_t *dev_to_remove)
+{
+	nvlist_t **newdev = NULL;
+
+	if (count > 1)
+		newdev = kmem_alloc((count - 1) * sizeof (void *), KM_SLEEP);
+
+	for (int i = 0, j = 0; i < count; i++) {
+		if (dev[i] == dev_to_remove)
+			continue;
+		VERIFY(nvlist_dup(dev[i], &newdev[j++], KM_SLEEP) == 0);
+	}
+
+	VERIFY(nvlist_remove(config, name, DATA_TYPE_NVLIST_ARRAY) == 0);
+	VERIFY(nvlist_add_nvlist_array(config, name, newdev, count - 1) == 0);
+
+	for (int i = 0; i < count - 1; i++)
+		nvlist_free(newdev[i]);
+
+	if (count > 1)
+		kmem_free(newdev, (count - 1) * sizeof (void *));
+}
+
+static spa_vdev_removal_t *
+spa_vdev_removal_create(vdev_t *vd)
+{
+	spa_vdev_removal_t *svr = kmem_zalloc(sizeof (*svr), KM_SLEEP);
+	mutex_init(&svr->svr_lock, NULL, MUTEX_DEFAULT, NULL);
+	cv_init(&svr->svr_cv, NULL, CV_DEFAULT, NULL);
+	svr->svr_allocd_segs = range_tree_create(NULL, NULL);
+	svr->svr_vdev = vd;
+
+	for (int i = 0; i < TXG_SIZE; i++) {
+		svr->svr_frees[i] = range_tree_create(NULL, NULL);
+		list_create(&svr->svr_new_segments[i],
+		    sizeof (vdev_indirect_mapping_entry_t),
+		    offsetof(vdev_indirect_mapping_entry_t, vime_node));
+	}
+
+	return (svr);
+}
+
+void
+spa_vdev_removal_destroy(spa_vdev_removal_t *svr)
+{
+	for (int i = 0; i < TXG_SIZE; i++) {
+		ASSERT0(svr->svr_bytes_done[i]);
+		ASSERT0(svr->svr_max_offset_to_sync[i]);
+		range_tree_destroy(svr->svr_frees[i]);
+		list_destroy(&svr->svr_new_segments[i]);
+	}
+
+	range_tree_destroy(svr->svr_allocd_segs);
+	mutex_destroy(&svr->svr_lock);
+	cv_destroy(&svr->svr_cv);
+	kmem_free(svr, sizeof (*svr));
+}
+
+/*
+ * This is called as a synctask in the txg in which we will mark this vdev
+ * as removing (in the config stored in the MOS).
+ *
+ * It begins the evacuation of a toplevel vdev by:
+ * - initializing the spa_removing_phys which tracks this removal
+ * - computing the amount of space to remove for accounting purposes
+ * - dirtying all dbufs in the spa_config_object
+ * - creating the spa_vdev_removal
+ * - starting the spa_vdev_remove_thread
+ */
+static void
+vdev_remove_initiate_sync(void *arg, dmu_tx_t *tx)
+{
+	vdev_t *vd = arg;
+	vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
+	spa_t *spa = vd->vdev_spa;
+	objset_t *mos = spa->spa_dsl_pool->dp_meta_objset;
+	spa_vdev_removal_t *svr = NULL;
+	ASSERTV(uint64_t txg = dmu_tx_get_txg(tx));
+
+	ASSERT3P(vd->vdev_ops, !=, &vdev_raidz_ops);
+	svr = spa_vdev_removal_create(vd);
+
+	ASSERT(vd->vdev_removing);
+	ASSERT3P(vd->vdev_indirect_mapping, ==, NULL);
+
+	spa_feature_incr(spa, SPA_FEATURE_DEVICE_REMOVAL, tx);
+	if (spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS)) {
+		/*
+		 * By activating the OBSOLETE_COUNTS feature, we prevent
+		 * the pool from being downgraded and ensure that the
+		 * refcounts are precise.
+		 */
+		spa_feature_incr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
+		uint64_t one = 1;
+		VERIFY0(zap_add(spa->spa_meta_objset, vd->vdev_top_zap,
+		    VDEV_TOP_ZAP_OBSOLETE_COUNTS_ARE_PRECISE, sizeof (one), 1,
+		    &one, tx));
+		ASSERT3U(vdev_obsolete_counts_are_precise(vd), !=, 0);
+	}
+
+	vic->vic_mapping_object = vdev_indirect_mapping_alloc(mos, tx);
+	vd->vdev_indirect_mapping =
+	    vdev_indirect_mapping_open(mos, vic->vic_mapping_object);
+	vic->vic_births_object = vdev_indirect_births_alloc(mos, tx);
+	vd->vdev_indirect_births =
+	    vdev_indirect_births_open(mos, vic->vic_births_object);
+	spa->spa_removing_phys.sr_removing_vdev = vd->vdev_id;
+	spa->spa_removing_phys.sr_start_time = gethrestime_sec();
+	spa->spa_removing_phys.sr_end_time = 0;
+	spa->spa_removing_phys.sr_state = DSS_SCANNING;
+	spa->spa_removing_phys.sr_to_copy = 0;
+	spa->spa_removing_phys.sr_copied = 0;
+
+	/*
+	 * Note: We can't use vdev_stat's vs_alloc for sr_to_copy, because
+	 * there may be space in the defer tree, which is free, but still
+	 * counted in vs_alloc.
+	 */
+	for (uint64_t i = 0; i < vd->vdev_ms_count; i++) {
+		metaslab_t *ms = vd->vdev_ms[i];
+		if (ms->ms_sm == NULL)
+			continue;
+
+		/*
+		 * Sync tasks happen before metaslab_sync(), therefore
+		 * smp_alloc and sm_alloc must be the same.
+		 */
+		ASSERT3U(space_map_allocated(ms->ms_sm), ==,
+		    ms->ms_sm->sm_phys->smp_alloc);
+
+		spa->spa_removing_phys.sr_to_copy +=
+		    space_map_allocated(ms->ms_sm);
+
+		/*
+		 * Space which we are freeing this txg does not need to
+		 * be copied.
+		 */
+		spa->spa_removing_phys.sr_to_copy -=
+		    range_tree_space(ms->ms_freeingtree);
+
+		ASSERT0(range_tree_space(ms->ms_freedtree));
+		for (int t = 0; t < TXG_SIZE; t++)
+			ASSERT0(range_tree_space(ms->ms_alloctree[t]));
+	}
+
+	/*
+	 * Sync tasks are called before metaslab_sync(), so there should
+	 * be no already-synced metaslabs in the TXG_CLEAN list.
+	 */
+	ASSERT3P(txg_list_head(&vd->vdev_ms_list, TXG_CLEAN(txg)), ==, NULL);
+
+	spa_sync_removing_state(spa, tx);
+
+	/*
+	 * All blocks that we need to read the most recent mapping must be
+	 * stored on concrete vdevs.  Therefore, we must dirty anything that
+	 * is read before spa_remove_init().  Specifically, the
+	 * spa_config_object.  (Note that although we already modified the
+	 * spa_config_object in spa_sync_removing_state, that may not have
+	 * modified all blocks of the object.)
+	 */
+	dmu_object_info_t doi;
+	VERIFY0(dmu_object_info(mos, DMU_POOL_DIRECTORY_OBJECT, &doi));
+	for (uint64_t offset = 0; offset < doi.doi_max_offset; ) {
+		dmu_buf_t *dbuf;
+		VERIFY0(dmu_buf_hold(mos, DMU_POOL_DIRECTORY_OBJECT,
+		    offset, FTAG, &dbuf, 0));
+		dmu_buf_will_dirty(dbuf, tx);
+		offset += dbuf->db_size;
+		dmu_buf_rele(dbuf, FTAG);
+	}
+
+	/*
+	 * Now that we've allocated the im_object, dirty the vdev to ensure
+	 * that the object gets written to the config on disk.
+	 */
+	vdev_config_dirty(vd);
+
+	zfs_dbgmsg("starting removal thread for vdev %llu (%p) in txg %llu "
+	    "im_obj=%llu", vd->vdev_id, vd, dmu_tx_get_txg(tx),
+	    vic->vic_mapping_object);
+
+	spa_history_log_internal(spa, "vdev remove started", tx,
+	    "%s vdev %llu %s", spa_name(spa), vd->vdev_id,
+	    (vd->vdev_path != NULL) ? vd->vdev_path : "-");
+	/*
+	 * Setting spa_vdev_removal causes subsequent frees to call
+	 * free_from_removing_vdev().  Note that we don't need any locking
+	 * because we are the sync thread, and metaslab_free_impl() is only
+	 * called from syncing context (potentially from a zio taskq thread,
+	 * but in any case only when there are outstanding free i/os, which
+	 * there are not).
+	 */
+	ASSERT3P(spa->spa_vdev_removal, ==, NULL);
+	spa->spa_vdev_removal = svr;
+	svr->svr_thread = thread_create(NULL, 0,
+	    spa_vdev_remove_thread, vd, 0, &p0, TS_RUN, minclsyspri);
+}
+
+/*
+ * When we are opening a pool, we must read the mapping for each
+ * indirect vdev in order from most recently removed to least
+ * recently removed.  We do this because the blocks for the mapping
+ * of older indirect vdevs may be stored on more recently removed vdevs.
+ * In order to read each indirect mapping object, we must have
+ * initialized all more recently removed vdevs.
+ */
+int
+spa_remove_init(spa_t *spa)
+{
+	int error;
+
+	error = zap_lookup(spa->spa_dsl_pool->dp_meta_objset,
+	    DMU_POOL_DIRECTORY_OBJECT,
+	    DMU_POOL_REMOVING, sizeof (uint64_t),
+	    sizeof (spa->spa_removing_phys) / sizeof (uint64_t),
+	    &spa->spa_removing_phys);
+
+	if (error == ENOENT) {
+		spa->spa_removing_phys.sr_state = DSS_NONE;
+		spa->spa_removing_phys.sr_removing_vdev = -1;
+		spa->spa_removing_phys.sr_prev_indirect_vdev = -1;
+		return (0);
+	} else if (error != 0) {
+		return (error);
+	}
+
+	if (spa->spa_removing_phys.sr_state == DSS_SCANNING) {
+		/*
+		 * We are currently removing a vdev.  Create and
+		 * initialize a spa_vdev_removal_t from the bonus
+		 * buffer of the removing vdevs vdev_im_object, and
+		 * initialize its partial mapping.
+		 */
+		spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
+		vdev_t *vd = vdev_lookup_top(spa,
+		    spa->spa_removing_phys.sr_removing_vdev);
+		spa_config_exit(spa, SCL_STATE, FTAG);
+
+		if (vd == NULL)
+			return (EINVAL);
+
+		vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
+
+		ASSERT(vdev_is_concrete(vd));
+		spa_vdev_removal_t *svr = spa_vdev_removal_create(vd);
+		ASSERT(svr->svr_vdev->vdev_removing);
+
+		vd->vdev_indirect_mapping = vdev_indirect_mapping_open(
+		    spa->spa_meta_objset, vic->vic_mapping_object);
+		vd->vdev_indirect_births = vdev_indirect_births_open(
+		    spa->spa_meta_objset, vic->vic_births_object);
+
+		spa->spa_vdev_removal = svr;
+	}
+
+	spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
+	uint64_t indirect_vdev_id =
+	    spa->spa_removing_phys.sr_prev_indirect_vdev;
+	while (indirect_vdev_id != UINT64_MAX) {
+		vdev_t *vd = vdev_lookup_top(spa, indirect_vdev_id);
+		vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
+
+		ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
+		vd->vdev_indirect_mapping = vdev_indirect_mapping_open(
+		    spa->spa_meta_objset, vic->vic_mapping_object);
+		vd->vdev_indirect_births = vdev_indirect_births_open(
+		    spa->spa_meta_objset, vic->vic_births_object);
+
+		indirect_vdev_id = vic->vic_prev_indirect_vdev;
+	}
+	spa_config_exit(spa, SCL_STATE, FTAG);
+
+	/*
+	 * Now that we've loaded all the indirect mappings, we can allow
+	 * reads from other blocks (e.g. via predictive prefetch).
+	 */
+	spa->spa_indirect_vdevs_loaded = B_TRUE;
+	return (0);
+}
+
+void
+spa_restart_removal(spa_t *spa)
+{
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+
+	if (svr == NULL)
+		return;
+
+	/*
+	 * In general when this function is called there is no
+	 * removal thread running. The only scenario where this
+	 * is not true is during spa_import() where this function
+	 * is called twice [once from spa_import_impl() and
+	 * spa_async_resume()]. Thus, in the scenario where we
+	 * import a pool that has an ongoing removal we don't
+	 * want to spawn a second thread.
+	 */
+	if (svr->svr_thread != NULL)
+		return;
+
+	if (!spa_writeable(spa))
+		return;
+
+	vdev_t *vd = svr->svr_vdev;
+	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+
+	ASSERT3P(vd, !=, NULL);
+	ASSERT(vd->vdev_removing);
+
+	zfs_dbgmsg("restarting removal of %llu at count=%llu",
+	    vd->vdev_id, vdev_indirect_mapping_num_entries(vim));
+	svr->svr_thread = thread_create(NULL, 0, spa_vdev_remove_thread, vd,
+	    0, &p0, TS_RUN, minclsyspri);
+}
+
+/*
+ * Process freeing from a device which is in the middle of being removed.
+ * We must handle this carefully so that we attempt to copy freed data,
+ * and we correctly free already-copied data.
+ */
+void
+free_from_removing_vdev(vdev_t *vd, uint64_t offset, uint64_t size,
+    uint64_t txg)
+{
+	spa_t *spa = vd->vdev_spa;
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+	uint64_t max_offset_yet = 0;
+
+	ASSERT(vd->vdev_indirect_config.vic_mapping_object != 0);
+	ASSERT3U(vd->vdev_indirect_config.vic_mapping_object, ==,
+	    vdev_indirect_mapping_object(vim));
+	ASSERT3P(vd, ==, svr->svr_vdev);
+	ASSERT3U(spa_syncing_txg(spa), ==, txg);
+
+	mutex_enter(&svr->svr_lock);
+
+	/*
+	 * Remove the segment from the removing vdev's spacemap.  This
+	 * ensures that we will not attempt to copy this space (if the
+	 * removal thread has not yet visited it), and also ensures
+	 * that we know what is actually allocated on the new vdevs
+	 * (needed if we cancel the removal).
+	 *
+	 * Note: we must do the metaslab_free_concrete() with the svr_lock
+	 * held, so that the remove_thread can not load this metaslab and then
+	 * visit this offset between the time that we metaslab_free_concrete()
+	 * and when we check to see if it has been visited.
+	 */
+	metaslab_free_concrete(vd, offset, size, txg);
+
+	uint64_t synced_size = 0;
+	uint64_t synced_offset = 0;
+	uint64_t max_offset_synced = vdev_indirect_mapping_max_offset(vim);
+	if (offset < max_offset_synced) {
+		/*
+		 * The mapping for this offset is already on disk.
+		 * Free from the new location.
+		 *
+		 * Note that we use svr_max_synced_offset because it is
+		 * updated atomically with respect to the in-core mapping.
+		 * By contrast, vim_max_offset is not.
+		 *
+		 * This block may be split between a synced entry and an
+		 * in-flight or unvisited entry.  Only process the synced
+		 * portion of it here.
+		 */
+		synced_size = MIN(size, max_offset_synced - offset);
+		synced_offset = offset;
+
+		ASSERT3U(max_offset_yet, <=, max_offset_synced);
+		max_offset_yet = max_offset_synced;
+
+		DTRACE_PROBE3(remove__free__synced,
+		    spa_t *, spa,
+		    uint64_t, offset,
+		    uint64_t, synced_size);
+
+		size -= synced_size;
+		offset += synced_size;
+	}
+
+	/*
+	 * Look at all in-flight txgs starting from the currently syncing one
+	 * and see if a section of this free is being copied. By starting from
+	 * this txg and iterating forward, we might find that this region
+	 * was copied in two different txgs and handle it appropriately.
+	 */
+	for (int i = 0; i < TXG_CONCURRENT_STATES; i++) {
+		int txgoff = (txg + i) & TXG_MASK;
+		if (size > 0 && offset < svr->svr_max_offset_to_sync[txgoff]) {
+			/*
+			 * The mapping for this offset is in flight, and
+			 * will be synced in txg+i.
+			 */
+			uint64_t inflight_size = MIN(size,
+			    svr->svr_max_offset_to_sync[txgoff] - offset);
+
+			DTRACE_PROBE4(remove__free__inflight,
+			    spa_t *, spa,
+			    uint64_t, offset,
+			    uint64_t, inflight_size,
+			    uint64_t, txg + i);
+
+			/*
+			 * We copy data in order of increasing offset.
+			 * Therefore the max_offset_to_sync[] must increase
+			 * (or be zero, indicating that nothing is being
+			 * copied in that txg).
+			 */
+			if (svr->svr_max_offset_to_sync[txgoff] != 0) {
+				ASSERT3U(svr->svr_max_offset_to_sync[txgoff],
+				    >=, max_offset_yet);
+				max_offset_yet =
+				    svr->svr_max_offset_to_sync[txgoff];
+			}
+
+			/*
+			 * We've already committed to copying this segment:
+			 * we have allocated space elsewhere in the pool for
+			 * it and have an IO outstanding to copy the data. We
+			 * cannot free the space before the copy has
+			 * completed, or else the copy IO might overwrite any
+			 * new data. To free that space, we record the
+			 * segment in the appropriate svr_frees tree and free
+			 * the mapped space later, in the txg where we have
+			 * completed the copy and synced the mapping (see
+			 * vdev_mapping_sync).
+			 */
+			range_tree_add(svr->svr_frees[txgoff],
+			    offset, inflight_size);
+			size -= inflight_size;
+			offset += inflight_size;
+
+			/*
+			 * This space is already accounted for as being
+			 * done, because it is being copied in txg+i.
+			 * However, if i!=0, then it is being copied in
+			 * a future txg.  If we crash after this txg
+			 * syncs but before txg+i syncs, then the space
+			 * will be free.  Therefore we must account
+			 * for the space being done in *this* txg
+			 * (when it is freed) rather than the future txg
+			 * (when it will be copied).
+			 */
+			ASSERT3U(svr->svr_bytes_done[txgoff], >=,
+			    inflight_size);
+			svr->svr_bytes_done[txgoff] -= inflight_size;
+			svr->svr_bytes_done[txg & TXG_MASK] += inflight_size;
+		}
+	}
+	ASSERT0(svr->svr_max_offset_to_sync[TXG_CLEAN(txg) & TXG_MASK]);
+
+	if (size > 0) {
+		/*
+		 * The copy thread has not yet visited this offset.  Ensure
+		 * that it doesn't.
+		 */
+
+		DTRACE_PROBE3(remove__free__unvisited,
+		    spa_t *, spa,
+		    uint64_t, offset,
+		    uint64_t, size);
+
+		if (svr->svr_allocd_segs != NULL)
+			range_tree_clear(svr->svr_allocd_segs, offset, size);
+
+		/*
+		 * Since we now do not need to copy this data, for
+		 * accounting purposes we have done our job and can count
+		 * it as completed.
+		 */
+		svr->svr_bytes_done[txg & TXG_MASK] += size;
+	}
+	mutex_exit(&svr->svr_lock);
+
+	/*
+	 * Now that we have dropped svr_lock, process the synced portion
+	 * of this free.
+	 */
+	if (synced_size > 0) {
+		vdev_indirect_mark_obsolete(vd, synced_offset, synced_size,
+		    txg);
+		/*
+		 * Note: this can only be called from syncing context,
+		 * and the vdev_indirect_mapping is only changed from the
+		 * sync thread, so we don't need svr_lock while doing
+		 * metaslab_free_impl_cb.
+		 */
+		vdev_indirect_ops.vdev_op_remap(vd, synced_offset, synced_size,
+		    metaslab_free_impl_cb, &txg);
+	}
+}
+
+/*
+ * Stop an active removal and update the spa_removing phys.
+ */
+static void
+spa_finish_removal(spa_t *spa, dsl_scan_state_t state, dmu_tx_t *tx)
+{
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+	ASSERT3U(dmu_tx_get_txg(tx), ==, spa_syncing_txg(spa));
+
+	/* Ensure the removal thread has completed before we free the svr. */
+	spa_vdev_remove_suspend(spa);
+
+	ASSERT(state == DSS_FINISHED || state == DSS_CANCELED);
+
+	if (state == DSS_FINISHED) {
+		spa_removing_phys_t *srp = &spa->spa_removing_phys;
+		vdev_t *vd = svr->svr_vdev;
+		vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
+
+		if (srp->sr_prev_indirect_vdev != UINT64_MAX) {
+			vdev_t *pvd;
+			pvd = vdev_lookup_top(spa,
+			    srp->sr_prev_indirect_vdev);
+			ASSERT3P(pvd->vdev_ops, ==, &vdev_indirect_ops);
+		}
+
+		vic->vic_prev_indirect_vdev = srp->sr_prev_indirect_vdev;
+		srp->sr_prev_indirect_vdev = vd->vdev_id;
+	}
+	spa->spa_removing_phys.sr_state = state;
+	spa->spa_removing_phys.sr_end_time = gethrestime_sec();
+
+	spa->spa_vdev_removal = NULL;
+	spa_vdev_removal_destroy(svr);
+
+	spa_sync_removing_state(spa, tx);
+
+	vdev_config_dirty(spa->spa_root_vdev);
+}
+
+static void
+free_mapped_segment_cb(void *arg, uint64_t offset, uint64_t size)
+{
+	vdev_t *vd = arg;
+	vdev_indirect_mark_obsolete(vd, offset, size,
+	    vd->vdev_spa->spa_syncing_txg);
+	vdev_indirect_ops.vdev_op_remap(vd, offset, size,
+	    metaslab_free_impl_cb, &vd->vdev_spa->spa_syncing_txg);
+}
+
+/*
+ * On behalf of the removal thread, syncs an incremental bit more of
+ * the indirect mapping to disk and updates the in-memory mapping.
+ * Called as a sync task in every txg that the removal thread makes progress.
+ */
+static void
+vdev_mapping_sync(void *arg, dmu_tx_t *tx)
+{
+	spa_vdev_removal_t *svr = arg;
+	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
+	vdev_t *vd = svr->svr_vdev;
+	ASSERTV(vdev_indirect_config_t *vic = &vd->vdev_indirect_config);
+	uint64_t txg = dmu_tx_get_txg(tx);
+	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+
+	ASSERT(vic->vic_mapping_object != 0);
+	ASSERT3U(txg, ==, spa_syncing_txg(spa));
+
+	vdev_indirect_mapping_add_entries(vim,
+	    &svr->svr_new_segments[txg & TXG_MASK], tx);
+	vdev_indirect_births_add_entry(vd->vdev_indirect_births,
+	    vdev_indirect_mapping_max_offset(vim), dmu_tx_get_txg(tx), tx);
+
+	/*
+	 * Free the copied data for anything that was freed while the
+	 * mapping entries were in flight.
+	 */
+	mutex_enter(&svr->svr_lock);
+	range_tree_vacate(svr->svr_frees[txg & TXG_MASK],
+	    free_mapped_segment_cb, vd);
+	ASSERT3U(svr->svr_max_offset_to_sync[txg & TXG_MASK], >=,
+	    vdev_indirect_mapping_max_offset(vim));
+	svr->svr_max_offset_to_sync[txg & TXG_MASK] = 0;
+	mutex_exit(&svr->svr_lock);
+
+	spa_sync_removing_state(spa, tx);
+}
+
+static void
+spa_vdev_copy_segment_write_done(zio_t *zio)
+{
+	vdev_copy_seg_arg_t *vcsa = zio->io_private;
+	vdev_copy_arg_t *vca = vcsa->vcsa_copy_arg;
+	spa_config_exit(zio->io_spa, SCL_STATE, FTAG);
+	abd_free(zio->io_abd);
+
+	mutex_enter(&vca->vca_lock);
+	vca->vca_outstanding_bytes -= zio->io_size;
+	cv_signal(&vca->vca_cv);
+	mutex_exit(&vca->vca_lock);
+
+	ASSERT0(zio->io_error);
+	kmem_free(vcsa->vcsa_dest_bp, sizeof (blkptr_t));
+	kmem_free(vcsa, sizeof (vdev_copy_seg_arg_t));
+}
+
+static void
+spa_vdev_copy_segment_read_done(zio_t *zio)
+{
+	vdev_copy_seg_arg_t *vcsa = zio->io_private;
+	dva_t *dest_dva = vcsa->vcsa_dest_dva;
+	uint64_t txg = vcsa->vcsa_txg;
+	spa_t *spa = zio->io_spa;
+	ASSERTV(vdev_t *dest_vd = vdev_lookup_top(spa, DVA_GET_VDEV(dest_dva)));
+	blkptr_t *bp = NULL;
+	dva_t *dva = NULL;
+	uint64_t size = zio->io_size;
+
+	ASSERT3P(dest_vd, !=, NULL);
+	ASSERT0(zio->io_error);
+
+	vcsa->vcsa_dest_bp = kmem_alloc(sizeof (blkptr_t), KM_SLEEP);
+	bp = vcsa->vcsa_dest_bp;
+	dva = bp->blk_dva;
+
+	BP_ZERO(bp);
+
+	/* initialize with dest_dva */
+	bcopy(dest_dva, dva, sizeof (dva_t));
+	BP_SET_BIRTH(bp, TXG_INITIAL, TXG_INITIAL);
+
+	BP_SET_LSIZE(bp, size);
+	BP_SET_PSIZE(bp, size);
+	BP_SET_COMPRESS(bp, ZIO_COMPRESS_OFF);
+	BP_SET_CHECKSUM(bp, ZIO_CHECKSUM_OFF);
+	BP_SET_TYPE(bp, DMU_OT_NONE);
+	BP_SET_LEVEL(bp, 0);
+	BP_SET_DEDUP(bp, 0);
+	BP_SET_BYTEORDER(bp, ZFS_HOST_BYTEORDER);
+
+	zio_nowait(zio_rewrite(spa->spa_txg_zio[txg & TXG_MASK], spa,
+	    txg, bp, zio->io_abd, size,
+	    spa_vdev_copy_segment_write_done, vcsa,
+	    ZIO_PRIORITY_REMOVAL, 0, NULL));
+}
+
+static int
+spa_vdev_copy_segment(vdev_t *vd, uint64_t start, uint64_t size, uint64_t txg,
+    vdev_copy_arg_t *vca, zio_alloc_list_t *zal)
+{
+	metaslab_group_t *mg = vd->vdev_mg;
+	spa_t *spa = vd->vdev_spa;
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+	vdev_indirect_mapping_entry_t *entry;
+	vdev_copy_seg_arg_t *private;
+	dva_t dst = {{ 0 }};
+	blkptr_t blk, *bp = &blk;
+	dva_t *dva = bp->blk_dva;
+
+	ASSERT3U(size, <=, SPA_MAXBLOCKSIZE);
+
+	int error = metaslab_alloc_dva(spa, mg->mg_class, size,
+	    &dst, 0, NULL, txg, 0, zal);
+	if (error != 0)
+		return (error);
+
+	/*
+	 * We can't have any padding of the allocated size, otherwise we will
+	 * misunderstand what's allocated, and the size of the mapping.
+	 * The caller ensures this will be true by passing in a size that is
+	 * aligned to the worst (highest) ashift in the pool.
+	 */
+	ASSERT3U(DVA_GET_ASIZE(&dst), ==, size);
+
+	mutex_enter(&vca->vca_lock);
+	vca->vca_outstanding_bytes += size;
+	mutex_exit(&vca->vca_lock);
+
+	entry = kmem_zalloc(sizeof (vdev_indirect_mapping_entry_t), KM_SLEEP);
+	DVA_MAPPING_SET_SRC_OFFSET(&entry->vime_mapping, start);
+	entry->vime_mapping.vimep_dst = dst;
+
+	private = kmem_alloc(sizeof (vdev_copy_seg_arg_t), KM_SLEEP);
+	private->vcsa_dest_dva = &entry->vime_mapping.vimep_dst;
+	private->vcsa_txg = txg;
+	private->vcsa_copy_arg = vca;
+
+	/*
+	 * This lock is eventually released by the donefunc for the
+	 * zio_write_phys that finishes copying the data.
+	 */
+	spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
+
+	/*
+	 * Do logical I/O, letting the redundancy vdevs (like mirror)
+	 * handle their own I/O instead of duplicating that code here.
+	 */
+	BP_ZERO(bp);
+
+	DVA_SET_VDEV(&dva[0], vd->vdev_id);
+	DVA_SET_OFFSET(&dva[0], start);
+	DVA_SET_GANG(&dva[0], 0);
+	DVA_SET_ASIZE(&dva[0], vdev_psize_to_asize(vd, size));
+
+	BP_SET_BIRTH(bp, TXG_INITIAL, TXG_INITIAL);
+
+	BP_SET_LSIZE(bp, size);
+	BP_SET_PSIZE(bp, size);
+	BP_SET_COMPRESS(bp, ZIO_COMPRESS_OFF);
+	BP_SET_CHECKSUM(bp, ZIO_CHECKSUM_OFF);
+	BP_SET_TYPE(bp, DMU_OT_NONE);
+	BP_SET_LEVEL(bp, 0);
+	BP_SET_DEDUP(bp, 0);
+	BP_SET_BYTEORDER(bp, ZFS_HOST_BYTEORDER);
+
+	zio_nowait(zio_read(spa->spa_txg_zio[txg & TXG_MASK], spa,
+	    bp, abd_alloc_for_io(size, B_FALSE), size,
+	    spa_vdev_copy_segment_read_done, private,
+	    ZIO_PRIORITY_REMOVAL, 0, NULL));
+
+	list_insert_tail(&svr->svr_new_segments[txg & TXG_MASK], entry);
+	ASSERT3U(start + size, <=, vd->vdev_ms_count << vd->vdev_ms_shift);
+	vdev_dirty(vd, 0, NULL, txg);
+
+	return (0);
+}
+
+/*
+ * Complete the removal of a toplevel vdev. This is called as a
+ * synctask in the same txg that we will sync out the new config (to the
+ * MOS object) which indicates that this vdev is indirect.
+ */
+static void
+vdev_remove_complete_sync(void *arg, dmu_tx_t *tx)
+{
+	spa_vdev_removal_t *svr = arg;
+	vdev_t *vd = svr->svr_vdev;
+	spa_t *spa = vd->vdev_spa;
+
+	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
+
+	for (int i = 0; i < TXG_SIZE; i++) {
+		ASSERT0(svr->svr_bytes_done[i]);
+	}
+
+	ASSERT3U(spa->spa_removing_phys.sr_copied, ==,
+	    spa->spa_removing_phys.sr_to_copy);
+
+	vdev_destroy_spacemaps(vd, tx);
+
+	/* destroy leaf zaps, if any */
+	ASSERT3P(svr->svr_zaplist, !=, NULL);
+	for (nvpair_t *pair = nvlist_next_nvpair(svr->svr_zaplist, NULL);
+	    pair != NULL;
+	    pair = nvlist_next_nvpair(svr->svr_zaplist, pair)) {
+		vdev_destroy_unlink_zap(vd, fnvpair_value_uint64(pair), tx);
+	}
+	fnvlist_free(svr->svr_zaplist);
+
+	spa_finish_removal(dmu_tx_pool(tx)->dp_spa, DSS_FINISHED, tx);
+	/* vd->vdev_path is not available here */
+	spa_history_log_internal(spa, "vdev remove completed",  tx,
+	    "%s vdev %llu", spa_name(spa), vd->vdev_id);
+}
+
+static void
+vdev_indirect_state_transfer(vdev_t *ivd, vdev_t *vd)
+{
+	ivd->vdev_indirect_config = vd->vdev_indirect_config;
+
+	ASSERT3P(ivd->vdev_indirect_mapping, ==, NULL);
+	ASSERT(vd->vdev_indirect_mapping != NULL);
+	ivd->vdev_indirect_mapping = vd->vdev_indirect_mapping;
+	vd->vdev_indirect_mapping = NULL;
+
+	ASSERT3P(ivd->vdev_indirect_births, ==, NULL);
+	ASSERT(vd->vdev_indirect_births != NULL);
+	ivd->vdev_indirect_births = vd->vdev_indirect_births;
+	vd->vdev_indirect_births = NULL;
+
+	ASSERT0(range_tree_space(vd->vdev_obsolete_segments));
+	ASSERT0(range_tree_space(ivd->vdev_obsolete_segments));
+
+	if (vd->vdev_obsolete_sm != NULL) {
+		ASSERT3U(ivd->vdev_asize, ==, vd->vdev_asize);
+
+		/*
+		 * We cannot use space_map_{open,close} because we hold all
+		 * the config locks as writer.
+		 */
+		ASSERT3P(ivd->vdev_obsolete_sm, ==, NULL);
+		ivd->vdev_obsolete_sm = vd->vdev_obsolete_sm;
+		vd->vdev_obsolete_sm = NULL;
+	}
+}
+
+static void
+vdev_remove_enlist_zaps(vdev_t *vd, nvlist_t *zlist)
+{
+	ASSERT3P(zlist, !=, NULL);
+	ASSERT3P(vd->vdev_ops, !=, &vdev_raidz_ops);
+
+	if (vd->vdev_leaf_zap != 0) {
+		char zkey[32];
+		(void) snprintf(zkey, sizeof (zkey), "%s-%llu",
+		    VDEV_REMOVAL_ZAP_OBJS, (u_longlong_t)vd->vdev_leaf_zap);
+		fnvlist_add_uint64(zlist, zkey, vd->vdev_leaf_zap);
+	}
+
+	for (uint64_t id = 0; id < vd->vdev_children; id++) {
+		vdev_remove_enlist_zaps(vd->vdev_child[id], zlist);
+	}
+}
+
+static void
+vdev_remove_replace_with_indirect(vdev_t *vd, uint64_t txg)
+{
+	vdev_t *ivd;
+	dmu_tx_t *tx;
+	spa_t *spa = vd->vdev_spa;
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+
+	/*
+	 * First, build a list of leaf zaps to be destroyed.
+	 * This is passed to the sync context thread,
+	 * which does the actual unlinking.
+	 */
+	svr->svr_zaplist = fnvlist_alloc();
+	vdev_remove_enlist_zaps(vd, svr->svr_zaplist);
+
+	ivd = vdev_add_parent(vd, &vdev_indirect_ops);
+
+	vd->vdev_leaf_zap = 0;
+
+	vdev_remove_child(ivd, vd);
+	vdev_compact_children(ivd);
+
+	vdev_indirect_state_transfer(ivd, vd);
+
+	svr->svr_vdev = ivd;
+
+	ASSERT(!ivd->vdev_removing);
+	ASSERT(!list_link_active(&vd->vdev_state_dirty_node));
+
+	tx = dmu_tx_create_assigned(spa->spa_dsl_pool, txg);
+	dsl_sync_task_nowait(spa->spa_dsl_pool, vdev_remove_complete_sync, svr,
+	    0, ZFS_SPACE_CHECK_NONE, tx);
+	dmu_tx_commit(tx);
+
+	/*
+	 * Indicate that this thread has exited.
+	 * After this, we can not use svr.
+	 */
+	mutex_enter(&svr->svr_lock);
+	svr->svr_thread = NULL;
+	cv_broadcast(&svr->svr_cv);
+	mutex_exit(&svr->svr_lock);
+}
+
+/*
+ * Complete the removal of a toplevel vdev. This is called in open
+ * context by the removal thread after we have copied all vdev's data.
+ */
+static void
+vdev_remove_complete(vdev_t *vd)
+{
+	spa_t *spa = vd->vdev_spa;
+	uint64_t txg;
+
+	/*
+	 * Wait for any deferred frees to be synced before we call
+	 * vdev_metaslab_fini()
+	 */
+	txg_wait_synced(spa->spa_dsl_pool, 0);
+
+	txg = spa_vdev_enter(spa);
+	zfs_dbgmsg("finishing device removal for vdev %llu in txg %llu",
+	    vd->vdev_id, txg);
+
+	/*
+	 * Discard allocation state.
+	 */
+	if (vd->vdev_mg != NULL) {
+		vdev_metaslab_fini(vd);
+		metaslab_group_destroy(vd->vdev_mg);
+		vd->vdev_mg = NULL;
+	}
+	ASSERT0(vd->vdev_stat.vs_space);
+	ASSERT0(vd->vdev_stat.vs_dspace);
+
+	vdev_remove_replace_with_indirect(vd, txg);
+
+	/*
+	 * We now release the locks, allowing spa_sync to run and finish the
+	 * removal via vdev_remove_complete_sync in syncing context.
+	 */
+	(void) spa_vdev_exit(spa, NULL, txg, 0);
+
+	/*
+	 * Top ZAP should have been transferred to the indirect vdev in
+	 * vdev_remove_replace_with_indirect.
+	 */
+	ASSERT0(vd->vdev_top_zap);
+
+	/*
+	 * Leaf ZAP should have been moved in vdev_remove_replace_with_indirect.
+	 */
+	ASSERT0(vd->vdev_leaf_zap);
+
+	txg = spa_vdev_enter(spa);
+	(void) vdev_label_init(vd, 0, VDEV_LABEL_REMOVE);
+	/*
+	 * Request to update the config and the config cachefile.
+	 */
+	vdev_config_dirty(spa->spa_root_vdev);
+	(void) spa_vdev_exit(spa, vd, txg, 0);
+}
+
+/*
+ * Evacuates a segment of size at most max_alloc from the vdev
+ * via repeated calls to spa_vdev_copy_segment. If an allocation
+ * fails, the pool is probably too fragmented to handle such a
+ * large size, so decrease max_alloc so that the caller will not try
+ * this size again this txg.
+ */
+static void
+spa_vdev_copy_impl(spa_vdev_removal_t *svr, vdev_copy_arg_t *vca,
+    uint64_t *max_alloc, dmu_tx_t *tx)
+{
+	uint64_t txg = dmu_tx_get_txg(tx);
+	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
+
+	mutex_enter(&svr->svr_lock);
+
+	range_seg_t *rs = avl_first(&svr->svr_allocd_segs->rt_root);
+	if (rs == NULL) {
+		mutex_exit(&svr->svr_lock);
+		return;
+	}
+	uint64_t offset = rs->rs_start;
+	uint64_t length = MIN(rs->rs_end - rs->rs_start, *max_alloc);
+
+	range_tree_remove(svr->svr_allocd_segs, offset, length);
+
+	if (svr->svr_max_offset_to_sync[txg & TXG_MASK] == 0) {
+		dsl_sync_task_nowait(dmu_tx_pool(tx), vdev_mapping_sync,
+		    svr, 0, ZFS_SPACE_CHECK_NONE, tx);
+	}
+
+	svr->svr_max_offset_to_sync[txg & TXG_MASK] = offset + length;
+
+	/*
+	 * Note: this is the amount of *allocated* space
+	 * that we are taking care of each txg.
+	 */
+	svr->svr_bytes_done[txg & TXG_MASK] += length;
+
+	mutex_exit(&svr->svr_lock);
+
+	zio_alloc_list_t zal;
+	metaslab_trace_init(&zal);
+	uint64_t thismax = *max_alloc;
+	while (length > 0) {
+		uint64_t mylen = MIN(length, thismax);
+
+		int error = spa_vdev_copy_segment(svr->svr_vdev,
+		    offset, mylen, txg, vca, &zal);
+
+		if (error == ENOSPC) {
+			/*
+			 * Cut our segment in half, and don't try this
+			 * segment size again this txg.  Note that the
+			 * allocation size must be aligned to the highest
+			 * ashift in the pool, so that the allocation will
+			 * not be padded out to a multiple of the ashift,
+			 * which could cause us to think that this mapping
+			 * is larger than we intended.
+			 */
+			ASSERT3U(spa->spa_max_ashift, >=, SPA_MINBLOCKSHIFT);
+			ASSERT3U(spa->spa_max_ashift, ==, spa->spa_min_ashift);
+			thismax = P2ROUNDUP(mylen / 2,
+			    1 << spa->spa_max_ashift);
+			ASSERT3U(thismax, <, mylen);
+			/*
+			 * The minimum-size allocation can not fail.
+			 */
+			ASSERT3U(mylen, >, 1 << spa->spa_max_ashift);
+			*max_alloc = mylen - (1 << spa->spa_max_ashift);
+		} else {
+			ASSERT0(error);
+			length -= mylen;
+			offset += mylen;
+
+			/*
+			 * We've performed an allocation, so reset the
+			 * alloc trace list.
+			 */
+			metaslab_trace_fini(&zal);
+			metaslab_trace_init(&zal);
+		}
+	}
+	metaslab_trace_fini(&zal);
+}
+
+/*
+ * The removal thread operates in open context.  It iterates over all
+ * allocated space in the vdev, by loading each metaslab's spacemap.
+ * For each contiguous segment of allocated space (capping the segment
+ * size at SPA_MAXBLOCKSIZE), we:
+ *    - Allocate space for it on another vdev.
+ *    - Create a new mapping from the old location to the new location
+ *      (as a record in svr_new_segments).
+ *    - Initiate a physical read zio to get the data off the removing disk.
+ *    - In the read zio's done callback, initiate a physical write zio to
+ *      write it to the new vdev.
+ * Note that all of this will take effect when a particular TXG syncs.
+ * The sync thread ensures that all the phys reads and writes for the syncing
+ * TXG have completed (see spa_txg_zio) and writes the new mappings to disk
+ * (see vdev_mapping_sync()).
+ */
+static void
+spa_vdev_remove_thread(void *arg)
+{
+	vdev_t *vd = arg;
+	spa_t *spa = vd->vdev_spa;
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+	vdev_copy_arg_t vca;
+	uint64_t max_alloc = zfs_remove_max_segment;
+	uint64_t last_txg = 0;
+	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+	uint64_t start_offset = vdev_indirect_mapping_max_offset(vim);
+
+	ASSERT3P(vd->vdev_ops, !=, &vdev_indirect_ops);
+	ASSERT(vdev_is_concrete(vd));
+	ASSERT(vd->vdev_removing);
+	ASSERT(vd->vdev_indirect_config.vic_mapping_object != 0);
+	ASSERT3P(svr->svr_vdev, ==, vd);
+	ASSERT(vim != NULL);
+
+	mutex_init(&vca.vca_lock, NULL, MUTEX_DEFAULT, NULL);
+	cv_init(&vca.vca_cv, NULL, CV_DEFAULT, NULL);
+	vca.vca_outstanding_bytes = 0;
+
+	mutex_enter(&svr->svr_lock);
+
+	/*
+	 * Start from vim_max_offset so we pick up where we left off
+	 * if we are restarting the removal after opening the pool.
+	 */
+	uint64_t msi;
+	for (msi = start_offset >> vd->vdev_ms_shift;
+	    msi < vd->vdev_ms_count && !svr->svr_thread_exit; msi++) {
+		metaslab_t *msp = vd->vdev_ms[msi];
+		ASSERT3U(msi, <=, vd->vdev_ms_count);
+
+		ASSERT0(range_tree_space(svr->svr_allocd_segs));
+
+		mutex_enter(&msp->ms_sync_lock);
+		mutex_enter(&msp->ms_lock);
+
+		/*
+		 * Assert nothing in flight -- ms_*tree is empty.
+		 */
+		for (int i = 0; i < TXG_SIZE; i++) {
+			ASSERT0(range_tree_space(msp->ms_alloctree[i]));
+		}
+
+		/*
+		 * If the metaslab has ever been allocated from (ms_sm!=NULL),
+		 * read the allocated segments from the space map object
+		 * into svr_allocd_segs. Since we do this while holding
+		 * svr_lock and ms_sync_lock, concurrent frees (which
+		 * would have modified the space map) will wait for us
+		 * to finish loading the spacemap, and then take the
+		 * appropriate action (see free_from_removing_vdev()).
+		 */
+		if (msp->ms_sm != NULL) {
+			space_map_t *sm = NULL;
+
+			/*
+			 * We have to open a new space map here, because
+			 * ms_sm's sm_length and sm_alloc may not reflect
+			 * what's in the object contents, if we are in between
+			 * metaslab_sync() and metaslab_sync_done().
+			 */
+			VERIFY0(space_map_open(&sm,
+			    spa->spa_dsl_pool->dp_meta_objset,
+			    msp->ms_sm->sm_object, msp->ms_sm->sm_start,
+			    msp->ms_sm->sm_size, msp->ms_sm->sm_shift));
+			space_map_update(sm);
+			VERIFY0(space_map_load(sm, svr->svr_allocd_segs,
+			    SM_ALLOC));
+			space_map_close(sm);
+
+			range_tree_walk(msp->ms_freeingtree,
+			    range_tree_remove, svr->svr_allocd_segs);
+
+			/*
+			 * When we are resuming from a paused removal (i.e.
+			 * when importing a pool with a removal in progress),
+			 * discard any state that we have already processed.
+			 */
+			range_tree_clear(svr->svr_allocd_segs, 0, start_offset);
+		}
+		mutex_exit(&msp->ms_lock);
+		mutex_exit(&msp->ms_sync_lock);
+
+		vca.vca_msp = msp;
+		zfs_dbgmsg("copying %llu segments for metaslab %llu",
+		    avl_numnodes(&svr->svr_allocd_segs->rt_root),
+		    msp->ms_id);
+
+		while (!svr->svr_thread_exit &&
+		    range_tree_space(svr->svr_allocd_segs) != 0) {
+
+			mutex_exit(&svr->svr_lock);
+
+			mutex_enter(&vca.vca_lock);
+			while (vca.vca_outstanding_bytes >
+			    zfs_remove_max_copy_bytes) {
+				cv_wait(&vca.vca_cv, &vca.vca_lock);
+			}
+			mutex_exit(&vca.vca_lock);
+
+			dmu_tx_t *tx =
+			    dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
+			dmu_tx_hold_space(tx, SPA_MAXBLOCKSIZE);
+			VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
+			uint64_t txg = dmu_tx_get_txg(tx);
+
+			if (txg != last_txg)
+				max_alloc = zfs_remove_max_segment;
+			last_txg = txg;
+
+			spa_vdev_copy_impl(svr, &vca, &max_alloc, tx);
+
+			dmu_tx_commit(tx);
+			mutex_enter(&svr->svr_lock);
+		}
+	}
+
+	mutex_exit(&svr->svr_lock);
+	/*
+	 * Wait for all copies to finish before cleaning up the vca.
+	 */
+	txg_wait_synced(spa->spa_dsl_pool, 0);
+	ASSERT0(vca.vca_outstanding_bytes);
+
+	mutex_destroy(&vca.vca_lock);
+	cv_destroy(&vca.vca_cv);
+
+	if (svr->svr_thread_exit) {
+		mutex_enter(&svr->svr_lock);
+		range_tree_vacate(svr->svr_allocd_segs, NULL, NULL);
+		svr->svr_thread = NULL;
+		cv_broadcast(&svr->svr_cv);
+		mutex_exit(&svr->svr_lock);
+	} else {
+		ASSERT0(range_tree_space(svr->svr_allocd_segs));
+		vdev_remove_complete(vd);
+	}
+}
+
+void
+spa_vdev_remove_suspend(spa_t *spa)
+{
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+
+	if (svr == NULL)
+		return;
+
+	mutex_enter(&svr->svr_lock);
+	svr->svr_thread_exit = B_TRUE;
+	while (svr->svr_thread != NULL)
+		cv_wait(&svr->svr_cv, &svr->svr_lock);
+	svr->svr_thread_exit = B_FALSE;
+	mutex_exit(&svr->svr_lock);
+}
+
+/* ARGSUSED */
+static int
+spa_vdev_remove_cancel_check(void *arg, dmu_tx_t *tx)
+{
+	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
+
+	if (spa->spa_vdev_removal == NULL)
+		return (ENOTACTIVE);
+	return (0);
+}
+
+/*
+ * Cancel a removal by freeing all entries from the partial mapping
+ * and marking the vdev as no longer being removing.
+ */
+/* ARGSUSED */
+static void
+spa_vdev_remove_cancel_sync(void *arg, dmu_tx_t *tx)
+{
+	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+	vdev_t *vd = svr->svr_vdev;
+	vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
+	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+	objset_t *mos = spa->spa_meta_objset;
+
+	ASSERT3P(svr->svr_thread, ==, NULL);
+
+	spa_feature_decr(spa, SPA_FEATURE_DEVICE_REMOVAL, tx);
+	if (vdev_obsolete_counts_are_precise(vd)) {
+		spa_feature_decr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
+		VERIFY0(zap_remove(spa->spa_meta_objset, vd->vdev_top_zap,
+		    VDEV_TOP_ZAP_OBSOLETE_COUNTS_ARE_PRECISE, tx));
+	}
+
+	if (vdev_obsolete_sm_object(vd) != 0) {
+		ASSERT(vd->vdev_obsolete_sm != NULL);
+		ASSERT3U(vdev_obsolete_sm_object(vd), ==,
+		    space_map_object(vd->vdev_obsolete_sm));
+
+		space_map_free(vd->vdev_obsolete_sm, tx);
+		VERIFY0(zap_remove(spa->spa_meta_objset, vd->vdev_top_zap,
+		    VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM, tx));
+		space_map_close(vd->vdev_obsolete_sm);
+		vd->vdev_obsolete_sm = NULL;
+		spa_feature_decr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
+	}
+	for (int i = 0; i < TXG_SIZE; i++) {
+		ASSERT(list_is_empty(&svr->svr_new_segments[i]));
+		ASSERT3U(svr->svr_max_offset_to_sync[i], <=,
+		    vdev_indirect_mapping_max_offset(vim));
+	}
+
+	for (uint64_t msi = 0; msi < vd->vdev_ms_count; msi++) {
+		metaslab_t *msp = vd->vdev_ms[msi];
+
+		if (msp->ms_start >= vdev_indirect_mapping_max_offset(vim))
+			break;
+
+		ASSERT0(range_tree_space(svr->svr_allocd_segs));
+
+		mutex_enter(&msp->ms_lock);
+
+		/*
+		 * Assert nothing in flight -- ms_*tree is empty.
+		 */
+		for (int i = 0; i < TXG_SIZE; i++)
+			ASSERT0(range_tree_space(msp->ms_alloctree[i]));
+		for (int i = 0; i < TXG_DEFER_SIZE; i++)
+			ASSERT0(range_tree_space(msp->ms_defertree[i]));
+		ASSERT0(range_tree_space(msp->ms_freedtree));
+
+		if (msp->ms_sm != NULL) {
+			/*
+			 * Assert that the in-core spacemap has the same
+			 * length as the on-disk one, so we can use the
+			 * existing in-core spacemap to load it from disk.
+			 */
+			ASSERT3U(msp->ms_sm->sm_alloc, ==,
+			    msp->ms_sm->sm_phys->smp_alloc);
+			ASSERT3U(msp->ms_sm->sm_length, ==,
+			    msp->ms_sm->sm_phys->smp_objsize);
+
+			mutex_enter(&svr->svr_lock);
+			VERIFY0(space_map_load(msp->ms_sm,
+			    svr->svr_allocd_segs, SM_ALLOC));
+			range_tree_walk(msp->ms_freeingtree,
+			    range_tree_remove, svr->svr_allocd_segs);
+
+			/*
+			 * Clear everything past what has been synced,
+			 * because we have not allocated mappings for it yet.
+			 */
+			uint64_t syncd = vdev_indirect_mapping_max_offset(vim);
+			range_tree_clear(svr->svr_allocd_segs, syncd,
+			    msp->ms_sm->sm_start + msp->ms_sm->sm_size - syncd);
+
+			mutex_exit(&svr->svr_lock);
+		}
+		mutex_exit(&msp->ms_lock);
+
+		mutex_enter(&svr->svr_lock);
+		range_tree_vacate(svr->svr_allocd_segs,
+		    free_mapped_segment_cb, vd);
+		mutex_exit(&svr->svr_lock);
+	}
+
+	/*
+	 * Note: this must happen after we invoke free_mapped_segment_cb,
+	 * because it adds to the obsolete_segments.
+	 */
+	range_tree_vacate(vd->vdev_obsolete_segments, NULL, NULL);
+
+	ASSERT3U(vic->vic_mapping_object, ==,
+	    vdev_indirect_mapping_object(vd->vdev_indirect_mapping));
+	vdev_indirect_mapping_close(vd->vdev_indirect_mapping);
+	vd->vdev_indirect_mapping = NULL;
+	vdev_indirect_mapping_free(mos, vic->vic_mapping_object, tx);
+	vic->vic_mapping_object = 0;
+
+	ASSERT3U(vic->vic_births_object, ==,
+	    vdev_indirect_births_object(vd->vdev_indirect_births));
+	vdev_indirect_births_close(vd->vdev_indirect_births);
+	vd->vdev_indirect_births = NULL;
+	vdev_indirect_births_free(mos, vic->vic_births_object, tx);
+	vic->vic_births_object = 0;
+
+	/*
+	 * We may have processed some frees from the removing vdev in this
+	 * txg, thus increasing svr_bytes_done; discard that here to
+	 * satisfy the assertions in spa_vdev_removal_destroy().
+	 * Note that future txg's can not have any bytes_done, because
+	 * future TXG's are only modified from open context, and we have
+	 * already shut down the copying thread.
+	 */
+	svr->svr_bytes_done[dmu_tx_get_txg(tx) & TXG_MASK] = 0;
+	spa_finish_removal(spa, DSS_CANCELED, tx);
+
+	vd->vdev_removing = B_FALSE;
+	vdev_config_dirty(vd);
+
+	zfs_dbgmsg("canceled device removal for vdev %llu in %llu",
+	    vd->vdev_id, dmu_tx_get_txg(tx));
+	spa_history_log_internal(spa, "vdev remove canceled", tx,
+	    "%s vdev %llu %s", spa_name(spa),
+	    vd->vdev_id, (vd->vdev_path != NULL) ? vd->vdev_path : "-");
+}
+
+int
+spa_vdev_remove_cancel(spa_t *spa)
+{
+	spa_vdev_remove_suspend(spa);
+
+	if (spa->spa_vdev_removal == NULL)
+		return (ENOTACTIVE);
+
+	uint64_t vdid = spa->spa_vdev_removal->svr_vdev->vdev_id;
+
+	int error = dsl_sync_task(spa->spa_name, spa_vdev_remove_cancel_check,
+	    spa_vdev_remove_cancel_sync, NULL, 0, ZFS_SPACE_CHECK_NONE);
+
+	if (error == 0) {
+		spa_config_enter(spa, SCL_ALLOC | SCL_VDEV, FTAG, RW_WRITER);
+		vdev_t *vd = vdev_lookup_top(spa, vdid);
+		metaslab_group_activate(vd->vdev_mg);
+		spa_config_exit(spa, SCL_ALLOC | SCL_VDEV, FTAG);
+	}
+
+	return (error);
+}
+
+/*
+ * Called every sync pass of every txg if there's a svr.
+ */
+void
+svr_sync(spa_t *spa, dmu_tx_t *tx)
+{
+	spa_vdev_removal_t *svr = spa->spa_vdev_removal;
+	int txgoff = dmu_tx_get_txg(tx) & TXG_MASK;
+
+	/*
+	 * This check is necessary so that we do not dirty the
+	 * DIRECTORY_OBJECT via spa_sync_removing_state() when there
+	 * is nothing to do.  Dirtying it every time would prevent us
+	 * from syncing-to-convergence.
+	 */
+	if (svr->svr_bytes_done[txgoff] == 0)
+		return;
+
+	/*
+	 * Update progress accounting.
+	 */
+	spa->spa_removing_phys.sr_copied += svr->svr_bytes_done[txgoff];
+	svr->svr_bytes_done[txgoff] = 0;
+
+	spa_sync_removing_state(spa, tx);
+}
+
+static void
+vdev_remove_make_hole_and_free(vdev_t *vd)
+{
+	uint64_t id = vd->vdev_id;
+	spa_t *spa = vd->vdev_spa;
+	vdev_t *rvd = spa->spa_root_vdev;
+	boolean_t last_vdev = (id == (rvd->vdev_children - 1));
+
+	ASSERT(MUTEX_HELD(&spa_namespace_lock));
+	ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
+
+	vdev_free(vd);
+
+	if (last_vdev) {
+		vdev_compact_children(rvd);
+	} else {
+		vd = vdev_alloc_common(spa, id, 0, &vdev_hole_ops);
+		vdev_add_child(rvd, vd);
+	}
+	vdev_config_dirty(rvd);
+
+	/*
+	 * Reassess the health of our root vdev.
+	 */
+	vdev_reopen(rvd);
+}
+
+/*
+ * Remove a log device.  The config lock is held for the specified TXG.
+ */
+static int
+spa_vdev_remove_log(vdev_t *vd, uint64_t *txg)
+{
+	metaslab_group_t *mg = vd->vdev_mg;
+	spa_t *spa = vd->vdev_spa;
+	int error = 0;
+
+	ASSERT(vd->vdev_islog);
+	ASSERT(vd == vd->vdev_top);
+
+	/*
+	 * Stop allocating from this vdev.
+	 */
+	metaslab_group_passivate(mg);
+
+	/*
+	 * Wait for the youngest allocations and frees to sync,
+	 * and then wait for the deferral of those frees to finish.
+	 */
+	spa_vdev_config_exit(spa, NULL,
+	    *txg + TXG_CONCURRENT_STATES + TXG_DEFER_SIZE, 0, FTAG);
+
+	/*
+	 * Evacuate the device.  We don't hold the config lock as writer
+	 * since we need to do I/O but we do keep the
+	 * spa_namespace_lock held.  Once this completes the device
+	 * should no longer have any blocks allocated on it.
+	 */
+	if (vd->vdev_islog) {
+		if (vd->vdev_stat.vs_alloc != 0)
+			error = spa_reset_logs(spa);
+	}
+
+	*txg = spa_vdev_config_enter(spa);
+
+	if (error != 0) {
+		metaslab_group_activate(mg);
+		return (error);
+	}
+	ASSERT0(vd->vdev_stat.vs_alloc);
+
+	/*
+	 * The evacuation succeeded.  Remove any remaining MOS metadata
+	 * associated with this vdev, and wait for these changes to sync.
+	 */
+	vd->vdev_removing = B_TRUE;
+
+	vdev_dirty_leaves(vd, VDD_DTL, *txg);
+	vdev_config_dirty(vd);
+
+	spa_history_log_internal(spa, "vdev remove", NULL,
+	    "%s vdev %llu (log) %s", spa_name(spa), vd->vdev_id,
+	    (vd->vdev_path != NULL) ? vd->vdev_path : "-");
+
+	spa_vdev_config_exit(spa, NULL, *txg, 0, FTAG);
+
+	*txg = spa_vdev_config_enter(spa);
+
+	sysevent_t *ev = spa_event_create(spa, vd, NULL,
+	    ESC_ZFS_VDEV_REMOVE_DEV);
+	ASSERT(MUTEX_HELD(&spa_namespace_lock));
+	ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
+
+	/* The top ZAP should have been destroyed by vdev_remove_empty. */
+	ASSERT0(vd->vdev_top_zap);
+	/* The leaf ZAP should have been destroyed by vdev_dtl_sync. */
+	ASSERT0(vd->vdev_leaf_zap);
+
+	(void) vdev_label_init(vd, 0, VDEV_LABEL_REMOVE);
+
+	if (list_link_active(&vd->vdev_state_dirty_node))
+		vdev_state_clean(vd);
+	if (list_link_active(&vd->vdev_config_dirty_node))
+		vdev_config_clean(vd);
+
+	/*
+	 * Clean up the vdev namespace.
+	 */
+	vdev_remove_make_hole_and_free(vd);
+
+	if (ev != NULL)
+		spa_event_post(ev);
+
+	return (0);
+}
+
+static int
+spa_vdev_remove_top_check(vdev_t *vd)
+{
+	spa_t *spa = vd->vdev_spa;
+
+	if (vd != vd->vdev_top)
+		return (SET_ERROR(ENOTSUP));
+
+	if (!spa_feature_is_enabled(spa, SPA_FEATURE_DEVICE_REMOVAL))
+		return (SET_ERROR(ENOTSUP));
+
+	/*
+	 * There has to be enough free space to remove the
+	 * device and leave double the "slop" space (i.e. we
+	 * must leave at least 3% of the pool free, in addition to
+	 * the normal slop space).
+	 */
+	if (dsl_dir_space_available(spa->spa_dsl_pool->dp_root_dir,
+	    NULL, 0, B_TRUE) <
+	    vd->vdev_stat.vs_dspace + spa_get_slop_space(spa)) {
+		return (SET_ERROR(ENOSPC));
+	}
+
+	/*
+	 * There can not be a removal in progress.
+	 */
+	if (spa->spa_removing_phys.sr_state == DSS_SCANNING)
+		return (SET_ERROR(EBUSY));
+
+	/*
+	 * The device must have all its data.
+	 */
+	if (!vdev_dtl_empty(vd, DTL_MISSING) ||
+	    !vdev_dtl_empty(vd, DTL_OUTAGE))
+		return (SET_ERROR(EBUSY));
+
+	/*
+	 * The device must be healthy.
+	 */
+	if (!vdev_readable(vd))
+		return (SET_ERROR(EIO));
+
+	/*
+	 * All vdevs in normal class must have the same ashift.
+	 */
+	if (spa->spa_max_ashift != spa->spa_min_ashift) {
+		return (SET_ERROR(EINVAL));
+	}
+
+	/*
+	 * All vdevs in normal class must have the same ashift
+	 * and not be raidz.
+	 */
+	vdev_t *rvd = spa->spa_root_vdev;
+	int num_indirect = 0;
+	for (uint64_t id = 0; id < rvd->vdev_children; id++) {
+		vdev_t *cvd = rvd->vdev_child[id];
+		if (cvd->vdev_ashift != 0 && !cvd->vdev_islog)
+			ASSERT3U(cvd->vdev_ashift, ==, spa->spa_max_ashift);
+		if (cvd->vdev_ops == &vdev_indirect_ops)
+			num_indirect++;
+		if (!vdev_is_concrete(cvd))
+			continue;
+		if (cvd->vdev_ops == &vdev_raidz_ops)
+			return (SET_ERROR(EINVAL));
+		/*
+		 * Need the mirror to be mirror of leaf vdevs only
+		 */
+		if (cvd->vdev_ops == &vdev_mirror_ops) {
+			for (uint64_t cid = 0;
+			    cid < cvd->vdev_children; cid++) {
+				if (!cvd->vdev_child[cid]->vdev_ops->
+				    vdev_op_leaf)
+					return (SET_ERROR(EINVAL));
+			}
+		}
+	}
+
+	return (0);
+}
+
+/*
+ * Initiate removal of a top-level vdev, reducing the total space in the pool.
+ * The config lock is held for the specified TXG.  Once initiated,
+ * evacuation of all allocated space (copying it to other vdevs) happens
+ * in the background (see spa_vdev_remove_thread()), and can be canceled
+ * (see spa_vdev_remove_cancel()).  If successful, the vdev will
+ * be transformed to an indirect vdev (see spa_vdev_remove_complete()).
+ */
+static int
+spa_vdev_remove_top(vdev_t *vd, uint64_t *txg)
+{
+	spa_t *spa = vd->vdev_spa;
+	int error;
+
+	/*
+	 * Check for errors up-front, so that we don't waste time
+	 * passivating the metaslab group and clearing the ZIL if there
+	 * are errors.
+	 */
+	error = spa_vdev_remove_top_check(vd);
+	if (error != 0)
+		return (error);
+
+	/*
+	 * Stop allocating from this vdev.  Note that we must check
+	 * that this is not the only device in the pool before
+	 * passivating, otherwise we will not be able to make
+	 * progress because we can't allocate from any vdevs.
+	 * The above check for sufficient free space serves this
+	 * purpose.
+	 */
+	metaslab_group_t *mg = vd->vdev_mg;
+	metaslab_group_passivate(mg);
+
+	/*
+	 * Wait for the youngest allocations and frees to sync,
+	 * and then wait for the deferral of those frees to finish.
+	 */
+	spa_vdev_config_exit(spa, NULL,
+	    *txg + TXG_CONCURRENT_STATES + TXG_DEFER_SIZE, 0, FTAG);
+
+	/*
+	 * We must ensure that no "stubby" log blocks are allocated
+	 * on the device to be removed.  These blocks could be
+	 * written at any time, including while we are in the middle
+	 * of copying them.
+	 */
+	error = spa_reset_logs(spa);
+
+	*txg = spa_vdev_config_enter(spa);
+
+	/*
+	 * Things might have changed while the config lock was dropped
+	 * (e.g. space usage).  Check for errors again.
+	 */
+	if (error == 0)
+		error = spa_vdev_remove_top_check(vd);
+
+	if (error != 0) {
+		metaslab_group_activate(mg);
+		return (error);
+	}
+
+	vd->vdev_removing = B_TRUE;
+
+	vdev_dirty_leaves(vd, VDD_DTL, *txg);
+	vdev_config_dirty(vd);
+	dmu_tx_t *tx = dmu_tx_create_assigned(spa->spa_dsl_pool, *txg);
+	dsl_sync_task_nowait(spa->spa_dsl_pool,
+	    vdev_remove_initiate_sync,
+	    vd, 0, ZFS_SPACE_CHECK_NONE, tx);
+	dmu_tx_commit(tx);
+
+	return (0);
+}
+
+/*
+ * Remove a device from the pool.
+ *
+ * Removing a device from the vdev namespace requires several steps
+ * and can take a significant amount of time.  As a result we use
+ * the spa_vdev_config_[enter/exit] functions which allow us to
+ * grab and release the spa_config_lock while still holding the namespace
+ * lock.  During each step the configuration is synced out.
+ */
+int
+spa_vdev_remove(spa_t *spa, uint64_t guid, boolean_t unspare)
+{
+	vdev_t *vd;
+	nvlist_t **spares, **l2cache, *nv;
+	uint64_t txg = 0;
+	uint_t nspares, nl2cache;
+	int error = 0;
+	boolean_t locked = MUTEX_HELD(&spa_namespace_lock);
+	sysevent_t *ev = NULL;
+
+	ASSERT(spa_writeable(spa));
+
+	if (!locked)
+		txg = spa_vdev_enter(spa);
+
+	vd = spa_lookup_by_guid(spa, guid, B_FALSE);
+
+	if (spa->spa_spares.sav_vdevs != NULL &&
+	    nvlist_lookup_nvlist_array(spa->spa_spares.sav_config,
+	    ZPOOL_CONFIG_SPARES, &spares, &nspares) == 0 &&
+	    (nv = spa_nvlist_lookup_by_guid(spares, nspares, guid)) != NULL) {
+		/*
+		 * Only remove the hot spare if it's not currently in use
+		 * in this pool.
+		 */
+		if (vd == NULL || unspare) {
+			if (vd == NULL)
+				vd = spa_lookup_by_guid(spa, guid, B_TRUE);
+			ev = spa_event_create(spa, vd, NULL,
+			    ESC_ZFS_VDEV_REMOVE_AUX);
+
+			char *nvstr = fnvlist_lookup_string(nv,
+			    ZPOOL_CONFIG_PATH);
+			spa_history_log_internal(spa, "vdev remove", NULL,
+			    "%s vdev (%s) %s", spa_name(spa),
+			    VDEV_TYPE_SPARE, nvstr);
+			spa_vdev_remove_aux(spa->spa_spares.sav_config,
+			    ZPOOL_CONFIG_SPARES, spares, nspares, nv);
+			spa_load_spares(spa);
+			spa->spa_spares.sav_sync = B_TRUE;
+		} else {
+			error = SET_ERROR(EBUSY);
+		}
+	} else if (spa->spa_l2cache.sav_vdevs != NULL &&
+	    nvlist_lookup_nvlist_array(spa->spa_l2cache.sav_config,
+	    ZPOOL_CONFIG_L2CACHE, &l2cache, &nl2cache) == 0 &&
+	    (nv = spa_nvlist_lookup_by_guid(l2cache, nl2cache, guid)) != NULL) {
+		char *nvstr = fnvlist_lookup_string(nv, ZPOOL_CONFIG_PATH);
+		spa_history_log_internal(spa, "vdev remove", NULL,
+		    "%s vdev (%s) %s", spa_name(spa), VDEV_TYPE_L2CACHE, nvstr);
+		/*
+		 * Cache devices can always be removed.
+		 */
+		vd = spa_lookup_by_guid(spa, guid, B_TRUE);
+		ev = spa_event_create(spa, vd, NULL, ESC_ZFS_VDEV_REMOVE_AUX);
+		spa_vdev_remove_aux(spa->spa_l2cache.sav_config,
+		    ZPOOL_CONFIG_L2CACHE, l2cache, nl2cache, nv);
+		spa_load_l2cache(spa);
+		spa->spa_l2cache.sav_sync = B_TRUE;
+	} else if (vd != NULL && vd->vdev_islog) {
+		ASSERT(!locked);
+		error = spa_vdev_remove_log(vd, &txg);
+	} else if (vd != NULL) {
+		ASSERT(!locked);
+		error = spa_vdev_remove_top(vd, &txg);
+	} else {
+		/*
+		 * There is no vdev of any kind with the specified guid.
+		 */
+		error = SET_ERROR(ENOENT);
+	}
+
+	if (!locked)
+		error = spa_vdev_exit(spa, NULL, txg, error);
+
+	if (ev != NULL)
+		spa_event_post(ev);
+
+	return (error);
+}
+
+int
+spa_removal_get_stats(spa_t *spa, pool_removal_stat_t *prs)
+{
+	prs->prs_state = spa->spa_removing_phys.sr_state;
+
+	if (prs->prs_state == DSS_NONE)
+		return (SET_ERROR(ENOENT));
+
+	prs->prs_removing_vdev = spa->spa_removing_phys.sr_removing_vdev;
+	prs->prs_start_time = spa->spa_removing_phys.sr_start_time;
+	prs->prs_end_time = spa->spa_removing_phys.sr_end_time;
+	prs->prs_to_copy = spa->spa_removing_phys.sr_to_copy;
+	prs->prs_copied = spa->spa_removing_phys.sr_copied;
+
+	if (spa->spa_vdev_removal != NULL) {
+		for (int i = 0; i < TXG_SIZE; i++) {
+			prs->prs_copied +=
+			    spa->spa_vdev_removal->svr_bytes_done[i];
+		}
+	}
+
+	prs->prs_mapping_memory = 0;
+	uint64_t indirect_vdev_id =
+	    spa->spa_removing_phys.sr_prev_indirect_vdev;
+	while (indirect_vdev_id != -1) {
+		vdev_t *vd = spa->spa_root_vdev->vdev_child[indirect_vdev_id];
+		vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
+		vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+
+		ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
+		prs->prs_mapping_memory += vdev_indirect_mapping_size(vim);
+		indirect_vdev_id = vic->vic_prev_indirect_vdev;
+	}
+
+	return (0);
+}
+
+#if defined(_KERNEL) && defined(HAVE_SPL)
+module_param(zfs_remove_max_segment, int, 0644);
+MODULE_PARM_DESC(zfs_remove_max_segment,
+	"Largest contiguous segment to allocate when removing device");
+
+EXPORT_SYMBOL(free_from_removing_vdev);
+EXPORT_SYMBOL(spa_removal_get_stats);
+EXPORT_SYMBOL(spa_remove_init);
+EXPORT_SYMBOL(spa_restart_removal);
+EXPORT_SYMBOL(spa_vdev_removal_destroy);
+EXPORT_SYMBOL(spa_vdev_remove);
+EXPORT_SYMBOL(spa_vdev_remove_cancel);
+EXPORT_SYMBOL(spa_vdev_remove_suspend);
+EXPORT_SYMBOL(svr_sync);
+#endif