OpenZFS 9102 - zfs should be able to initialize storage devices

PROBLEM
========

The first access to a block incurs a performance penalty on some platforms
(e.g. AWS's EBS, VMware VMDKs). Therefore we recommend that volumes are
"thick provisioned", where supported by the platform (VMware). This can
create a large delay in getting a new virtual machines up and running (or
adding storage to an existing Engine). If the thick provision step is
omitted, write performance will be suboptimal until all blocks on the LUN
have been written.

SOLUTION
=========

This feature introduces a way to 'initialize' the disks at install or in the
background to make sure we don't incur this first read penalty.

When an entire LUN is added to ZFS, we make all space available immediately,
and allow ZFS to find unallocated space and zero it out. This works with
concurrent writes to arbitrary offsets, ensuring that we don't zero out
something that has been (or is in the middle of being) written. This scheme
can also be applied to existing pools (affecting only free regions on the
vdev). Detailed design:
        - new subcommand:zpool initialize [-cs] <pool> [<vdev> ...]
                - start, suspend, or cancel initialization
        - Creates new open-context thread for each vdev
        - Thread iterates through all metaslabs in this vdev
        - Each metaslab:
                - select a metaslab
                - load the metaslab
                - mark the metaslab as being zeroed
                - walk all free ranges within that metaslab and translate
                  them to ranges on the leaf vdev
                - issue a "zeroing" I/O on the leaf vdev that corresponds to
                  a free range on the metaslab we're working on
                - continue until all free ranges for this metaslab have been
                  "zeroed"
                - reset/unmark the metaslab being zeroed
                - if more metaslabs exist, then repeat above tasks.
                - if no more metaslabs, then we're done.

        - progress for the initialization is stored on-disk in the vdev’s
          leaf zap object. The following information is stored:
                - the last offset that has been initialized
                - the state of the initialization process (i.e. active,
                  suspended, or canceled)
                - the start time for the initialization

        - progress is reported via the zpool status command and shows
          information for each of the vdevs that are initializing

Porting notes:
- Added zfs_initialize_value module parameter to set the pattern
  written by "zpool initialize".
- Added zfs_vdev_{initializing,removal}_{min,max}_active module options.

Authored by: George Wilson <[email protected]>
Reviewed by: John Wren Kennedy <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Pavel Zakharov <[email protected]>
Reviewed by: Prakash Surya <[email protected]>
Reviewed by: loli10K <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Approved by: Richard Lowe <[email protected]>
Signed-off-by: Tim Chase <[email protected]>
Ported-by: Tim Chase <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/9102
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/c3963210eb
Closes #8230

1 files changed, 819 insertions, 0 deletions

diff --git a/module/zfs/vdev_initialize.c b/module/zfs/vdev_initialize.c
new file mode 100644
index 000000000..fcd2c76f9
--- /dev/null
+++ b/module/zfs/vdev_initialize.c
@@ -0,0 +1,819 @@
+/*
+ * 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) 2016 by Delphix. All rights reserved.
+ */
+
+#include <sys/spa.h>
+#include <sys/spa_impl.h>
+#include <sys/txg.h>
+#include <sys/vdev_impl.h>
+#include <sys/refcount.h>
+#include <sys/metaslab_impl.h>
+#include <sys/dsl_synctask.h>
+#include <sys/zap.h>
+#include <sys/dmu_tx.h>
+
+/*
+ * Maximum number of metaslabs per group that can be initialized
+ * simultaneously.
+ */
+int max_initialize_ms = 3;
+
+/*
+ * Value that is written to disk during initialization.
+ */
+#ifdef _ILP32
+unsigned long zfs_initialize_value = 0xdeadbeefUL;
+#else
+unsigned long zfs_initialize_value = 0xdeadbeefdeadbeeeULL;
+#endif
+
+/* maximum number of I/Os outstanding per leaf vdev */
+int zfs_initialize_limit = 1;
+
+/* size of initializing writes; default 1MiB, see zfs_remove_max_segment */
+uint64_t zfs_initialize_chunk_size = 1024 * 1024;
+
+static boolean_t
+vdev_initialize_should_stop(vdev_t *vd)
+{
+	return (vd->vdev_initialize_exit_wanted || !vdev_writeable(vd) ||
+	    vd->vdev_detached || vd->vdev_top->vdev_removing);
+}
+
+static void
+vdev_initialize_zap_update_sync(void *arg, dmu_tx_t *tx)
+{
+	/*
+	 * We pass in the guid instead of the vdev_t since the vdev may
+	 * have been freed prior to the sync task being processed. This
+	 * happens when a vdev is detached as we call spa_config_vdev_exit(),
+	 * stop the intializing thread, schedule the sync task, and free
+	 * the vdev. Later when the scheduled sync task is invoked, it would
+	 * find that the vdev has been freed.
+	 */
+	uint64_t guid = *(uint64_t *)arg;
+	uint64_t txg = dmu_tx_get_txg(tx);
+	kmem_free(arg, sizeof (uint64_t));
+
+	vdev_t *vd = spa_lookup_by_guid(tx->tx_pool->dp_spa, guid, B_FALSE);
+	if (vd == NULL || vd->vdev_top->vdev_removing || !vdev_is_concrete(vd))
+		return;
+
+	uint64_t last_offset = vd->vdev_initialize_offset[txg & TXG_MASK];
+	vd->vdev_initialize_offset[txg & TXG_MASK] = 0;
+
+	VERIFY(vd->vdev_leaf_zap != 0);
+
+	objset_t *mos = vd->vdev_spa->spa_meta_objset;
+
+	if (last_offset > 0) {
+		vd->vdev_initialize_last_offset = last_offset;
+		VERIFY0(zap_update(mos, vd->vdev_leaf_zap,
+		    VDEV_LEAF_ZAP_INITIALIZE_LAST_OFFSET,
+		    sizeof (last_offset), 1, &last_offset, tx));
+	}
+	if (vd->vdev_initialize_action_time > 0) {
+		uint64_t val = (uint64_t)vd->vdev_initialize_action_time;
+		VERIFY0(zap_update(mos, vd->vdev_leaf_zap,
+		    VDEV_LEAF_ZAP_INITIALIZE_ACTION_TIME, sizeof (val),
+		    1, &val, tx));
+	}
+
+	uint64_t initialize_state = vd->vdev_initialize_state;
+	VERIFY0(zap_update(mos, vd->vdev_leaf_zap,
+	    VDEV_LEAF_ZAP_INITIALIZE_STATE, sizeof (initialize_state), 1,
+	    &initialize_state, tx));
+}
+
+static void
+vdev_initialize_change_state(vdev_t *vd, vdev_initializing_state_t new_state)
+{
+	ASSERT(MUTEX_HELD(&vd->vdev_initialize_lock));
+	spa_t *spa = vd->vdev_spa;
+
+	if (new_state == vd->vdev_initialize_state)
+		return;
+
+	/*
+	 * Copy the vd's guid, this will be freed by the sync task.
+	 */
+	uint64_t *guid = kmem_zalloc(sizeof (uint64_t), KM_SLEEP);
+	*guid = vd->vdev_guid;
+
+	/*
+	 * If we're suspending, then preserving the original start time.
+	 */
+	if (vd->vdev_initialize_state != VDEV_INITIALIZE_SUSPENDED) {
+		vd->vdev_initialize_action_time = gethrestime_sec();
+	}
+	vd->vdev_initialize_state = new_state;
+
+	dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
+	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
+	dsl_sync_task_nowait(spa_get_dsl(spa), vdev_initialize_zap_update_sync,
+	    guid, 2, ZFS_SPACE_CHECK_RESERVED, tx);
+
+	switch (new_state) {
+	case VDEV_INITIALIZE_ACTIVE:
+		spa_history_log_internal(spa, "initialize", tx,
+		    "vdev=%s activated", vd->vdev_path);
+		break;
+	case VDEV_INITIALIZE_SUSPENDED:
+		spa_history_log_internal(spa, "initialize", tx,
+		    "vdev=%s suspended", vd->vdev_path);
+		break;
+	case VDEV_INITIALIZE_CANCELED:
+		spa_history_log_internal(spa, "initialize", tx,
+		    "vdev=%s canceled", vd->vdev_path);
+		break;
+	case VDEV_INITIALIZE_COMPLETE:
+		spa_history_log_internal(spa, "initialize", tx,
+		    "vdev=%s complete", vd->vdev_path);
+		break;
+	default:
+		panic("invalid state %llu", (unsigned long long)new_state);
+	}
+
+	dmu_tx_commit(tx);
+}
+
+static void
+vdev_initialize_cb(zio_t *zio)
+{
+	vdev_t *vd = zio->io_vd;
+	mutex_enter(&vd->vdev_initialize_io_lock);
+	if (zio->io_error == ENXIO && !vdev_writeable(vd)) {
+		/*
+		 * The I/O failed because the vdev was unavailable; roll the
+		 * last offset back. (This works because spa_sync waits on
+		 * spa_txg_zio before it runs sync tasks.)
+		 */
+		uint64_t *off =
+		    &vd->vdev_initialize_offset[zio->io_txg & TXG_MASK];
+		*off = MIN(*off, zio->io_offset);
+	} else {
+		/*
+		 * Since initializing is best-effort, we ignore I/O errors and
+		 * rely on vdev_probe to determine if the errors are more
+		 * critical.
+		 */
+		if (zio->io_error != 0)
+			vd->vdev_stat.vs_initialize_errors++;
+
+		vd->vdev_initialize_bytes_done += zio->io_orig_size;
+	}
+	ASSERT3U(vd->vdev_initialize_inflight, >, 0);
+	vd->vdev_initialize_inflight--;
+	cv_broadcast(&vd->vdev_initialize_io_cv);
+	mutex_exit(&vd->vdev_initialize_io_lock);
+
+	spa_config_exit(vd->vdev_spa, SCL_STATE_ALL, vd);
+}
+
+/* Takes care of physical writing and limiting # of concurrent ZIOs. */
+static int
+vdev_initialize_write(vdev_t *vd, uint64_t start, uint64_t size, abd_t *data)
+{
+	spa_t *spa = vd->vdev_spa;
+
+	/* Limit inflight initializing I/Os */
+	mutex_enter(&vd->vdev_initialize_io_lock);
+	while (vd->vdev_initialize_inflight >= zfs_initialize_limit) {
+		cv_wait(&vd->vdev_initialize_io_cv,
+		    &vd->vdev_initialize_io_lock);
+	}
+	vd->vdev_initialize_inflight++;
+	mutex_exit(&vd->vdev_initialize_io_lock);
+
+	dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
+	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
+	uint64_t txg = dmu_tx_get_txg(tx);
+
+	spa_config_enter(spa, SCL_STATE_ALL, vd, RW_READER);
+	mutex_enter(&vd->vdev_initialize_lock);
+
+	if (vd->vdev_initialize_offset[txg & TXG_MASK] == 0) {
+		uint64_t *guid = kmem_zalloc(sizeof (uint64_t), KM_SLEEP);
+		*guid = vd->vdev_guid;
+
+		/* This is the first write of this txg. */
+		dsl_sync_task_nowait(spa_get_dsl(spa),
+		    vdev_initialize_zap_update_sync, guid, 2,
+		    ZFS_SPACE_CHECK_RESERVED, tx);
+	}
+
+	/*
+	 * We know the vdev struct will still be around since all
+	 * consumers of vdev_free must stop the initialization first.
+	 */
+	if (vdev_initialize_should_stop(vd)) {
+		mutex_enter(&vd->vdev_initialize_io_lock);
+		ASSERT3U(vd->vdev_initialize_inflight, >, 0);
+		vd->vdev_initialize_inflight--;
+		mutex_exit(&vd->vdev_initialize_io_lock);
+		spa_config_exit(vd->vdev_spa, SCL_STATE_ALL, vd);
+		mutex_exit(&vd->vdev_initialize_lock);
+		dmu_tx_commit(tx);
+		return (SET_ERROR(EINTR));
+	}
+	mutex_exit(&vd->vdev_initialize_lock);
+
+	vd->vdev_initialize_offset[txg & TXG_MASK] = start + size;
+	zio_nowait(zio_write_phys(spa->spa_txg_zio[txg & TXG_MASK], vd, start,
+	    size, data, ZIO_CHECKSUM_OFF, vdev_initialize_cb, NULL,
+	    ZIO_PRIORITY_INITIALIZING, ZIO_FLAG_CANFAIL, B_FALSE));
+	/* vdev_initialize_cb releases SCL_STATE_ALL */
+
+	dmu_tx_commit(tx);
+
+	return (0);
+}
+
+/*
+ * Translate a logical range to the physical range for the specified vdev_t.
+ * This function is initially called with a leaf vdev and will walk each
+ * parent vdev until it reaches a top-level vdev. Once the top-level is
+ * reached the physical range is initialized and the recursive function
+ * begins to unwind. As it unwinds it calls the parent's vdev specific
+ * translation function to do the real conversion.
+ */
+void
+vdev_xlate(vdev_t *vd, const range_seg_t *logical_rs, range_seg_t *physical_rs)
+{
+	/*
+	 * Walk up the vdev tree
+	 */
+	if (vd != vd->vdev_top) {
+		vdev_xlate(vd->vdev_parent, logical_rs, physical_rs);
+	} else {
+		/*
+		 * We've reached the top-level vdev, initialize the
+		 * physical range to the logical range and start to
+		 * unwind.
+		 */
+		physical_rs->rs_start = logical_rs->rs_start;
+		physical_rs->rs_end = logical_rs->rs_end;
+		return;
+	}
+
+	vdev_t *pvd = vd->vdev_parent;
+	ASSERT3P(pvd, !=, NULL);
+	ASSERT3P(pvd->vdev_ops->vdev_op_xlate, !=, NULL);
+
+	/*
+	 * As this recursive function unwinds, translate the logical
+	 * range into its physical components by calling the
+	 * vdev specific translate function.
+	 */
+	range_seg_t intermediate = { { { 0, 0 } } };
+	pvd->vdev_ops->vdev_op_xlate(vd, physical_rs, &intermediate);
+
+	physical_rs->rs_start = intermediate.rs_start;
+	physical_rs->rs_end = intermediate.rs_end;
+}
+
+/*
+ * Callback to fill each ABD chunk with zfs_initialize_value. len must be
+ * divisible by sizeof (uint64_t), and buf must be 8-byte aligned. The ABD
+ * allocation will guarantee these for us.
+ */
+/* ARGSUSED */
+static int
+vdev_initialize_block_fill(void *buf, size_t len, void *unused)
+{
+	ASSERT0(len % sizeof (uint64_t));
+#ifdef _ILP32
+	for (uint64_t i = 0; i < len; i += sizeof (uint32_t)) {
+		*(uint32_t *)((char *)(buf) + i) = zfs_initialize_value;
+	}
+#else
+	for (uint64_t i = 0; i < len; i += sizeof (uint64_t)) {
+		*(uint64_t *)((char *)(buf) + i) = zfs_initialize_value;
+	}
+#endif
+	return (0);
+}
+
+static abd_t *
+vdev_initialize_block_alloc(void)
+{
+	/* Allocate ABD for filler data */
+	abd_t *data = abd_alloc_for_io(zfs_initialize_chunk_size, B_FALSE);
+
+	ASSERT0(zfs_initialize_chunk_size % sizeof (uint64_t));
+	(void) abd_iterate_func(data, 0, zfs_initialize_chunk_size,
+	    vdev_initialize_block_fill, NULL);
+
+	return (data);
+}
+
+static void
+vdev_initialize_block_free(abd_t *data)
+{
+	abd_free(data);
+}
+
+static int
+vdev_initialize_ranges(vdev_t *vd, abd_t *data)
+{
+	avl_tree_t *rt = &vd->vdev_initialize_tree->rt_root;
+
+	for (range_seg_t *rs = avl_first(rt); rs != NULL;
+	    rs = AVL_NEXT(rt, rs)) {
+		uint64_t size = rs->rs_end - rs->rs_start;
+
+		/* Split range into legally-sized physical chunks */
+		uint64_t writes_required =
+		    ((size - 1) / zfs_initialize_chunk_size) + 1;
+
+		for (uint64_t w = 0; w < writes_required; w++) {
+			int error;
+
+			error = vdev_initialize_write(vd,
+			    VDEV_LABEL_START_SIZE + rs->rs_start +
+			    (w * zfs_initialize_chunk_size),
+			    MIN(size - (w * zfs_initialize_chunk_size),
+			    zfs_initialize_chunk_size), data);
+			if (error != 0)
+				return (error);
+		}
+	}
+	return (0);
+}
+
+static void
+vdev_initialize_ms_load(metaslab_t *msp)
+{
+	ASSERT(MUTEX_HELD(&msp->ms_lock));
+
+	metaslab_load_wait(msp);
+	if (!msp->ms_loaded)
+		VERIFY0(metaslab_load(msp));
+}
+
+static void
+vdev_initialize_mg_wait(metaslab_group_t *mg)
+{
+	ASSERT(MUTEX_HELD(&mg->mg_ms_initialize_lock));
+	while (mg->mg_initialize_updating) {
+		cv_wait(&mg->mg_ms_initialize_cv, &mg->mg_ms_initialize_lock);
+	}
+}
+
+static void
+vdev_initialize_mg_mark(metaslab_group_t *mg)
+{
+	ASSERT(MUTEX_HELD(&mg->mg_ms_initialize_lock));
+	ASSERT(mg->mg_initialize_updating);
+
+	while (mg->mg_ms_initializing >= max_initialize_ms) {
+		cv_wait(&mg->mg_ms_initialize_cv, &mg->mg_ms_initialize_lock);
+	}
+	mg->mg_ms_initializing++;
+	ASSERT3U(mg->mg_ms_initializing, <=, max_initialize_ms);
+}
+
+/*
+ * Mark the metaslab as being initialized to prevent any allocations
+ * on this metaslab. We must also track how many metaslabs are currently
+ * being initialized within a metaslab group and limit them to prevent
+ * allocation failures from occurring because all metaslabs are being
+ * initialized.
+ */
+static void
+vdev_initialize_ms_mark(metaslab_t *msp)
+{
+	ASSERT(!MUTEX_HELD(&msp->ms_lock));
+	metaslab_group_t *mg = msp->ms_group;
+
+	mutex_enter(&mg->mg_ms_initialize_lock);
+
+	/*
+	 * To keep an accurate count of how many threads are initializing
+	 * a specific metaslab group, we only allow one thread to mark
+	 * the metaslab group at a time. This ensures that the value of
+	 * ms_initializing will be accurate when we decide to mark a metaslab
+	 * group as being initialized. To do this we force all other threads
+	 * to wait till the metaslab's mg_initialize_updating flag is no
+	 * longer set.
+	 */
+	vdev_initialize_mg_wait(mg);
+	mg->mg_initialize_updating = B_TRUE;
+	if (msp->ms_initializing == 0) {
+		vdev_initialize_mg_mark(mg);
+	}
+	mutex_enter(&msp->ms_lock);
+	msp->ms_initializing++;
+	mutex_exit(&msp->ms_lock);
+
+	mg->mg_initialize_updating = B_FALSE;
+	cv_broadcast(&mg->mg_ms_initialize_cv);
+	mutex_exit(&mg->mg_ms_initialize_lock);
+}
+
+static void
+vdev_initialize_ms_unmark(metaslab_t *msp)
+{
+	ASSERT(!MUTEX_HELD(&msp->ms_lock));
+	metaslab_group_t *mg = msp->ms_group;
+	mutex_enter(&mg->mg_ms_initialize_lock);
+	mutex_enter(&msp->ms_lock);
+	if (--msp->ms_initializing == 0) {
+		mg->mg_ms_initializing--;
+		cv_broadcast(&mg->mg_ms_initialize_cv);
+	}
+	mutex_exit(&msp->ms_lock);
+	mutex_exit(&mg->mg_ms_initialize_lock);
+}
+
+static void
+vdev_initialize_calculate_progress(vdev_t *vd)
+{
+	ASSERT(spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_READER) ||
+	    spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_WRITER));
+	ASSERT(vd->vdev_leaf_zap != 0);
+
+	vd->vdev_initialize_bytes_est = 0;
+	vd->vdev_initialize_bytes_done = 0;
+
+	for (uint64_t i = 0; i < vd->vdev_top->vdev_ms_count; i++) {
+		metaslab_t *msp = vd->vdev_top->vdev_ms[i];
+		mutex_enter(&msp->ms_lock);
+
+		uint64_t ms_free = msp->ms_size -
+		    space_map_allocated(msp->ms_sm);
+
+		if (vd->vdev_top->vdev_ops == &vdev_raidz_ops)
+			ms_free /= vd->vdev_top->vdev_children;
+
+		/*
+		 * Convert the metaslab range to a physical range
+		 * on our vdev. We use this to determine if we are
+		 * in the middle of this metaslab range.
+		 */
+		range_seg_t logical_rs, physical_rs;
+		logical_rs.rs_start = msp->ms_start;
+		logical_rs.rs_end = msp->ms_start + msp->ms_size;
+		vdev_xlate(vd, &logical_rs, &physical_rs);
+
+		if (vd->vdev_initialize_last_offset <= physical_rs.rs_start) {
+			vd->vdev_initialize_bytes_est += ms_free;
+			mutex_exit(&msp->ms_lock);
+			continue;
+		} else if (vd->vdev_initialize_last_offset >
+		    physical_rs.rs_end) {
+			vd->vdev_initialize_bytes_done += ms_free;
+			vd->vdev_initialize_bytes_est += ms_free;
+			mutex_exit(&msp->ms_lock);
+			continue;
+		}
+
+		/*
+		 * If we get here, we're in the middle of initializing this
+		 * metaslab. Load it and walk the free tree for more accurate
+		 * progress estimation.
+		 */
+		vdev_initialize_ms_load(msp);
+
+		for (range_seg_t *rs = avl_first(&msp->ms_allocatable->rt_root);
+		    rs; rs = AVL_NEXT(&msp->ms_allocatable->rt_root, rs)) {
+			logical_rs.rs_start = rs->rs_start;
+			logical_rs.rs_end = rs->rs_end;
+			vdev_xlate(vd, &logical_rs, &physical_rs);
+
+			uint64_t size = physical_rs.rs_end -
+			    physical_rs.rs_start;
+			vd->vdev_initialize_bytes_est += size;
+			if (vd->vdev_initialize_last_offset >
+			    physical_rs.rs_end) {
+				vd->vdev_initialize_bytes_done += size;
+			} else if (vd->vdev_initialize_last_offset >
+			    physical_rs.rs_start &&
+			    vd->vdev_initialize_last_offset <
+			    physical_rs.rs_end) {
+				vd->vdev_initialize_bytes_done +=
+				    vd->vdev_initialize_last_offset -
+				    physical_rs.rs_start;
+			}
+		}
+		mutex_exit(&msp->ms_lock);
+	}
+}
+
+static int
+vdev_initialize_load(vdev_t *vd)
+{
+	int err = 0;
+	ASSERT(spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_READER) ||
+	    spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_WRITER));
+	ASSERT(vd->vdev_leaf_zap != 0);
+
+	if (vd->vdev_initialize_state == VDEV_INITIALIZE_ACTIVE ||
+	    vd->vdev_initialize_state == VDEV_INITIALIZE_SUSPENDED) {
+		err = zap_lookup(vd->vdev_spa->spa_meta_objset,
+		    vd->vdev_leaf_zap, VDEV_LEAF_ZAP_INITIALIZE_LAST_OFFSET,
+		    sizeof (vd->vdev_initialize_last_offset), 1,
+		    &vd->vdev_initialize_last_offset);
+		if (err == ENOENT) {
+			vd->vdev_initialize_last_offset = 0;
+			err = 0;
+		}
+	}
+
+	vdev_initialize_calculate_progress(vd);
+	return (err);
+}
+
+
+/*
+ * Convert the logical range into a physcial range and add it to our
+ * avl tree.
+ */
+void
+vdev_initialize_range_add(void *arg, uint64_t start, uint64_t size)
+{
+	vdev_t *vd = arg;
+	range_seg_t logical_rs, physical_rs;
+	logical_rs.rs_start = start;
+	logical_rs.rs_end = start + size;
+
+	ASSERT(vd->vdev_ops->vdev_op_leaf);
+	vdev_xlate(vd, &logical_rs, &physical_rs);
+
+	IMPLY(vd->vdev_top == vd,
+	    logical_rs.rs_start == physical_rs.rs_start);
+	IMPLY(vd->vdev_top == vd,
+	    logical_rs.rs_end == physical_rs.rs_end);
+
+	/* Only add segments that we have not visited yet */
+	if (physical_rs.rs_end <= vd->vdev_initialize_last_offset)
+		return;
+
+	/* Pick up where we left off mid-range. */
+	if (vd->vdev_initialize_last_offset > physical_rs.rs_start) {
+		zfs_dbgmsg("range write: vd %s changed (%llu, %llu) to "
+		    "(%llu, %llu)", vd->vdev_path,
+		    (u_longlong_t)physical_rs.rs_start,
+		    (u_longlong_t)physical_rs.rs_end,
+		    (u_longlong_t)vd->vdev_initialize_last_offset,
+		    (u_longlong_t)physical_rs.rs_end);
+		ASSERT3U(physical_rs.rs_end, >,
+		    vd->vdev_initialize_last_offset);
+		physical_rs.rs_start = vd->vdev_initialize_last_offset;
+	}
+	ASSERT3U(physical_rs.rs_end, >=, physical_rs.rs_start);
+
+	/*
+	 * With raidz, it's possible that the logical range does not live on
+	 * this leaf vdev. We only add the physical range to this vdev's if it
+	 * has a length greater than 0.
+	 */
+	if (physical_rs.rs_end > physical_rs.rs_start) {
+		range_tree_add(vd->vdev_initialize_tree, physical_rs.rs_start,
+		    physical_rs.rs_end - physical_rs.rs_start);
+	} else {
+		ASSERT3U(physical_rs.rs_end, ==, physical_rs.rs_start);
+	}
+}
+
+static void
+vdev_initialize_thread(void *arg)
+{
+	vdev_t *vd = arg;
+	spa_t *spa = vd->vdev_spa;
+	int error = 0;
+	uint64_t ms_count = 0;
+
+	ASSERT(vdev_is_concrete(vd));
+	spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
+
+	vd->vdev_initialize_last_offset = 0;
+	VERIFY0(vdev_initialize_load(vd));
+
+	abd_t *deadbeef = vdev_initialize_block_alloc();
+
+	vd->vdev_initialize_tree = range_tree_create(NULL, NULL);
+
+	for (uint64_t i = 0; !vd->vdev_detached &&
+	    i < vd->vdev_top->vdev_ms_count; i++) {
+		metaslab_t *msp = vd->vdev_top->vdev_ms[i];
+
+		/*
+		 * If we've expanded the top-level vdev or it's our
+		 * first pass, calculate our progress.
+		 */
+		if (vd->vdev_top->vdev_ms_count != ms_count) {
+			vdev_initialize_calculate_progress(vd);
+			ms_count = vd->vdev_top->vdev_ms_count;
+		}
+
+		vdev_initialize_ms_mark(msp);
+		mutex_enter(&msp->ms_lock);
+		vdev_initialize_ms_load(msp);
+
+		range_tree_walk(msp->ms_allocatable, vdev_initialize_range_add,
+		    vd);
+		mutex_exit(&msp->ms_lock);
+
+		spa_config_exit(spa, SCL_CONFIG, FTAG);
+		error = vdev_initialize_ranges(vd, deadbeef);
+		vdev_initialize_ms_unmark(msp);
+		spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
+
+		range_tree_vacate(vd->vdev_initialize_tree, NULL, NULL);
+		if (error != 0)
+			break;
+	}
+
+	spa_config_exit(spa, SCL_CONFIG, FTAG);
+	mutex_enter(&vd->vdev_initialize_io_lock);
+	while (vd->vdev_initialize_inflight > 0) {
+		cv_wait(&vd->vdev_initialize_io_cv,
+		    &vd->vdev_initialize_io_lock);
+	}
+	mutex_exit(&vd->vdev_initialize_io_lock);
+
+	range_tree_destroy(vd->vdev_initialize_tree);
+	vdev_initialize_block_free(deadbeef);
+	vd->vdev_initialize_tree = NULL;
+
+	mutex_enter(&vd->vdev_initialize_lock);
+	if (!vd->vdev_initialize_exit_wanted && vdev_writeable(vd)) {
+		vdev_initialize_change_state(vd, VDEV_INITIALIZE_COMPLETE);
+	}
+	ASSERT(vd->vdev_initialize_thread != NULL ||
+	    vd->vdev_initialize_inflight == 0);
+
+	/*
+	 * Drop the vdev_initialize_lock while we sync out the
+	 * txg since it's possible that a device might be trying to
+	 * come online and must check to see if it needs to restart an
+	 * initialization. That thread will be holding the spa_config_lock
+	 * which would prevent the txg_wait_synced from completing.
+	 */
+	mutex_exit(&vd->vdev_initialize_lock);
+	txg_wait_synced(spa_get_dsl(spa), 0);
+	mutex_enter(&vd->vdev_initialize_lock);
+
+	vd->vdev_initialize_thread = NULL;
+	cv_broadcast(&vd->vdev_initialize_cv);
+	mutex_exit(&vd->vdev_initialize_lock);
+}
+
+/*
+ * Initiates a device. Caller must hold vdev_initialize_lock.
+ * Device must be a leaf and not already be initializing.
+ */
+void
+vdev_initialize(vdev_t *vd)
+{
+	ASSERT(MUTEX_HELD(&vd->vdev_initialize_lock));
+	ASSERT(vd->vdev_ops->vdev_op_leaf);
+	ASSERT(vdev_is_concrete(vd));
+	ASSERT3P(vd->vdev_initialize_thread, ==, NULL);
+	ASSERT(!vd->vdev_detached);
+	ASSERT(!vd->vdev_initialize_exit_wanted);
+	ASSERT(!vd->vdev_top->vdev_removing);
+
+	vdev_initialize_change_state(vd, VDEV_INITIALIZE_ACTIVE);
+	vd->vdev_initialize_thread = thread_create(NULL, 0,
+	    vdev_initialize_thread, vd, 0, &p0, TS_RUN, maxclsyspri);
+}
+
+/*
+ * Stop initializng a device, with the resultant initialing state being
+ * tgt_state. Blocks until the initializing thread has exited.
+ * Caller must hold vdev_initialize_lock and must not be writing to the spa
+ * config, as the initializing thread may try to enter the config as a reader
+ * before exiting.
+ */
+void
+vdev_initialize_stop(vdev_t *vd, vdev_initializing_state_t tgt_state)
+{
+	ASSERTV(spa_t *spa = vd->vdev_spa);
+	ASSERT(!spa_config_held(spa, SCL_CONFIG | SCL_STATE, RW_WRITER));
+
+	ASSERT(MUTEX_HELD(&vd->vdev_initialize_lock));
+	ASSERT(vd->vdev_ops->vdev_op_leaf);
+	ASSERT(vdev_is_concrete(vd));
+
+	/*
+	 * Allow cancel requests to proceed even if the initialize thread
+	 * has stopped.
+	 */
+	if (vd->vdev_initialize_thread == NULL &&
+	    tgt_state != VDEV_INITIALIZE_CANCELED) {
+		return;
+	}
+
+	vdev_initialize_change_state(vd, tgt_state);
+	vd->vdev_initialize_exit_wanted = B_TRUE;
+	while (vd->vdev_initialize_thread != NULL)
+		cv_wait(&vd->vdev_initialize_cv, &vd->vdev_initialize_lock);
+
+	ASSERT3P(vd->vdev_initialize_thread, ==, NULL);
+	vd->vdev_initialize_exit_wanted = B_FALSE;
+}
+
+static void
+vdev_initialize_stop_all_impl(vdev_t *vd, vdev_initializing_state_t tgt_state)
+{
+	if (vd->vdev_ops->vdev_op_leaf && vdev_is_concrete(vd)) {
+		mutex_enter(&vd->vdev_initialize_lock);
+		vdev_initialize_stop(vd, tgt_state);
+		mutex_exit(&vd->vdev_initialize_lock);
+		return;
+	}
+
+	for (uint64_t i = 0; i < vd->vdev_children; i++) {
+		vdev_initialize_stop_all_impl(vd->vdev_child[i], tgt_state);
+	}
+}
+
+/*
+ * Convenience function to stop initializing of a vdev tree and set all
+ * initialize thread pointers to NULL.
+ */
+void
+vdev_initialize_stop_all(vdev_t *vd, vdev_initializing_state_t tgt_state)
+{
+	vdev_initialize_stop_all_impl(vd, tgt_state);
+
+	if (vd->vdev_spa->spa_sync_on) {
+		/* Make sure that our state has been synced to disk */
+		txg_wait_synced(spa_get_dsl(vd->vdev_spa), 0);
+	}
+}
+
+void
+vdev_initialize_restart(vdev_t *vd)
+{
+	ASSERT(MUTEX_HELD(&spa_namespace_lock));
+	ASSERT(!spa_config_held(vd->vdev_spa, SCL_ALL, RW_WRITER));
+
+	if (vd->vdev_leaf_zap != 0) {
+		mutex_enter(&vd->vdev_initialize_lock);
+		uint64_t initialize_state = VDEV_INITIALIZE_NONE;
+		int err = zap_lookup(vd->vdev_spa->spa_meta_objset,
+		    vd->vdev_leaf_zap, VDEV_LEAF_ZAP_INITIALIZE_STATE,
+		    sizeof (initialize_state), 1, &initialize_state);
+		ASSERT(err == 0 || err == ENOENT);
+		vd->vdev_initialize_state = initialize_state;
+
+		uint64_t timestamp = 0;
+		err = zap_lookup(vd->vdev_spa->spa_meta_objset,
+		    vd->vdev_leaf_zap, VDEV_LEAF_ZAP_INITIALIZE_ACTION_TIME,
+		    sizeof (timestamp), 1, &timestamp);
+		ASSERT(err == 0 || err == ENOENT);
+		vd->vdev_initialize_action_time = (time_t)timestamp;
+
+		if (vd->vdev_initialize_state == VDEV_INITIALIZE_SUSPENDED ||
+		    vd->vdev_offline) {
+			/* load progress for reporting, but don't resume */
+			VERIFY0(vdev_initialize_load(vd));
+		} else if (vd->vdev_initialize_state ==
+		    VDEV_INITIALIZE_ACTIVE && vdev_writeable(vd)) {
+			vdev_initialize(vd);
+		}
+
+		mutex_exit(&vd->vdev_initialize_lock);
+	}
+
+	for (uint64_t i = 0; i < vd->vdev_children; i++) {
+		vdev_initialize_restart(vd->vdev_child[i]);
+	}
+}
+
+#if defined(_KERNEL)
+EXPORT_SYMBOL(vdev_initialize_restart);
+EXPORT_SYMBOL(vdev_xlate);
+EXPORT_SYMBOL(vdev_initialize_stop_all);
+EXPORT_SYMBOL(vdev_initialize);
+EXPORT_SYMBOL(vdev_initialize_stop);
+
+/* CSTYLED */
+module_param(zfs_initialize_value, ulong, 0644);
+MODULE_PARM_DESC(zfs_initialize_value,
+	"Value written during zpool initialize");
+#endif