Fix typos in module/zfs/

[mirror_zfs.git] / module / zfs / vdev_mirror.c

/*
 * 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 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/spa_impl.h>
#include <sys/dsl_pool.h>
#include <sys/dsl_scan.h>
#include <sys/vdev_impl.h>
#include <sys/zio.h>
#include <sys/abd.h>
#include <sys/fs/zfs.h>

/*
 * Vdev mirror kstats
 */
static kstat_t *mirror_ksp = NULL;

typedef struct mirror_stats {
        kstat_named_t vdev_mirror_stat_rotating_linear;
        kstat_named_t vdev_mirror_stat_rotating_offset;
        kstat_named_t vdev_mirror_stat_rotating_seek;
        kstat_named_t vdev_mirror_stat_non_rotating_linear;
        kstat_named_t vdev_mirror_stat_non_rotating_seek;

        kstat_named_t vdev_mirror_stat_preferred_found;
        kstat_named_t vdev_mirror_stat_preferred_not_found;
} mirror_stats_t;

static mirror_stats_t mirror_stats = {
        /* New I/O follows directly the last I/O */
        { "rotating_linear",                    KSTAT_DATA_UINT64 },
        /* New I/O is within zfs_vdev_mirror_rotating_seek_offset of the last */
        { "rotating_offset",                    KSTAT_DATA_UINT64 },
        /* New I/O requires random seek */
        { "rotating_seek",                      KSTAT_DATA_UINT64 },
        /* New I/O follows directly the last I/O  (nonrot) */
        { "non_rotating_linear",                KSTAT_DATA_UINT64 },
        /* New I/O requires random seek (nonrot) */
        { "non_rotating_seek",                  KSTAT_DATA_UINT64 },
        /* Preferred child vdev found */
        { "preferred_found",                    KSTAT_DATA_UINT64 },
        /* Preferred child vdev not found or equal load  */
        { "preferred_not_found",                KSTAT_DATA_UINT64 },

};

#define MIRROR_STAT(stat)               (mirror_stats.stat.value.ui64)
#define MIRROR_INCR(stat, val)          atomic_add_64(&MIRROR_STAT(stat), val)
#define MIRROR_BUMP(stat)               MIRROR_INCR(stat, 1)

void
vdev_mirror_stat_init(void)
{
        mirror_ksp = kstat_create("zfs", 0, "vdev_mirror_stats",
            "misc", KSTAT_TYPE_NAMED,
            sizeof (mirror_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
        if (mirror_ksp != NULL) {
                mirror_ksp->ks_data = &mirror_stats;
                kstat_install(mirror_ksp);
        }
}

void
vdev_mirror_stat_fini(void)
{
        if (mirror_ksp != NULL) {
                kstat_delete(mirror_ksp);
                mirror_ksp = NULL;
        }
}

/*
 * Virtual device vector for mirroring.
 */

typedef struct mirror_child {
        vdev_t          *mc_vd;
        uint64_t        mc_offset;
        int             mc_error;
        int             mc_load;
        uint8_t         mc_tried;
        uint8_t         mc_skipped;
        uint8_t         mc_speculative;
} mirror_child_t;

typedef struct mirror_map {
        int             *mm_preferred;
        int             mm_preferred_cnt;
        int             mm_children;
        boolean_t       mm_resilvering;
        boolean_t       mm_root;
        mirror_child_t  mm_child[];
} mirror_map_t;

static int vdev_mirror_shift = 21;

/*
 * The load configuration settings below are tuned by default for
 * the case where all devices are of the same rotational type.
 *
 * If there is a mixture of rotating and non-rotating media, setting
 * zfs_vdev_mirror_non_rotating_seek_inc to 0 may well provide better results
 * as it will direct more reads to the non-rotating vdevs which are more likely
 * to have a higher performance.
 */

/* Rotating media load calculation configuration. */
static int zfs_vdev_mirror_rotating_inc = 0;
static int zfs_vdev_mirror_rotating_seek_inc = 5;
static int zfs_vdev_mirror_rotating_seek_offset = 1 * 1024 * 1024;

/* Non-rotating media load calculation configuration. */
static int zfs_vdev_mirror_non_rotating_inc = 0;
static int zfs_vdev_mirror_non_rotating_seek_inc = 1;

static inline size_t
vdev_mirror_map_size(int children)
{
        return (offsetof(mirror_map_t, mm_child[children]) +
            sizeof (int) * children);
}

static inline mirror_map_t *
vdev_mirror_map_alloc(int children, boolean_t resilvering, boolean_t root)
{
        mirror_map_t *mm;

        mm = kmem_zalloc(vdev_mirror_map_size(children), KM_SLEEP);
        mm->mm_children = children;
        mm->mm_resilvering = resilvering;
        mm->mm_root = root;
        mm->mm_preferred = (int *)((uintptr_t)mm +
            offsetof(mirror_map_t, mm_child[children]));

        return (mm);
}

static void
vdev_mirror_map_free(zio_t *zio)
{
        mirror_map_t *mm = zio->io_vsd;

        kmem_free(mm, vdev_mirror_map_size(mm->mm_children));
}

static const zio_vsd_ops_t vdev_mirror_vsd_ops = {
        .vsd_free = vdev_mirror_map_free,
        .vsd_cksum_report = zio_vsd_default_cksum_report
};

static int
vdev_mirror_load(mirror_map_t *mm, vdev_t *vd, uint64_t zio_offset)
{
        uint64_t last_offset;
        int64_t offset_diff;
        int load;

        /* All DVAs have equal weight at the root. */
        if (mm->mm_root)
                return (INT_MAX);

        /*
         * We don't return INT_MAX if the device is resilvering i.e.
         * vdev_resilver_txg != 0 as when tested performance was slightly
         * worse overall when resilvering with compared to without.
         */

        /* Fix zio_offset for leaf vdevs */
        if (vd->vdev_ops->vdev_op_leaf)
                zio_offset += VDEV_LABEL_START_SIZE;

        /* Standard load based on pending queue length. */
        load = vdev_queue_length(vd);
        last_offset = vdev_queue_last_offset(vd);

        if (vd->vdev_nonrot) {
                /* Non-rotating media. */
                if (last_offset == zio_offset) {
                        MIRROR_BUMP(vdev_mirror_stat_non_rotating_linear);
                        return (load + zfs_vdev_mirror_non_rotating_inc);
                }

                /*
                 * Apply a seek penalty even for non-rotating devices as
                 * sequential I/O's can be aggregated into fewer operations on
                 * the device, thus avoiding unnecessary per-command overhead
                 * and boosting performance.
                 */
                MIRROR_BUMP(vdev_mirror_stat_non_rotating_seek);
                return (load + zfs_vdev_mirror_non_rotating_seek_inc);
        }

        /* Rotating media I/O's which directly follow the last I/O. */
        if (last_offset == zio_offset) {
                MIRROR_BUMP(vdev_mirror_stat_rotating_linear);
                return (load + zfs_vdev_mirror_rotating_inc);
        }

        /*
         * Apply half the seek increment to I/O's within seek offset
         * of the last I/O issued to this vdev as they should incur less
         * of a seek increment.
         */
        offset_diff = (int64_t)(last_offset - zio_offset);
        if (ABS(offset_diff) < zfs_vdev_mirror_rotating_seek_offset) {
                MIRROR_BUMP(vdev_mirror_stat_rotating_offset);
                return (load + (zfs_vdev_mirror_rotating_seek_inc / 2));
        }

        /* Apply the full seek increment to all other I/O's. */
        MIRROR_BUMP(vdev_mirror_stat_rotating_seek);
        return (load + zfs_vdev_mirror_rotating_seek_inc);
}

/*
 * Avoid inlining the function to keep vdev_mirror_io_start(), which
 * is this functions only caller, as small as possible on the stack.
 */
noinline static mirror_map_t *
vdev_mirror_map_init(zio_t *zio)
{
        mirror_map_t *mm = NULL;
        mirror_child_t *mc;
        vdev_t *vd = zio->io_vd;
        int c;

        if (vd == NULL) {
                dva_t *dva = zio->io_bp->blk_dva;
                spa_t *spa = zio->io_spa;
                dsl_scan_t *scn = spa->spa_dsl_pool->dp_scan;
                dva_t dva_copy[SPA_DVAS_PER_BP];

                /*
                 * The sequential scrub code sorts and issues all DVAs
                 * of a bp separately. Each of these IOs includes all
                 * original DVA copies so that repairs can be performed
                 * in the event of an error, but we only actually want
                 * to check the first DVA since the others will be
                 * checked by their respective sorted IOs. Only if we
                 * hit an error will we try all DVAs upon retrying.
                 *
                 * Note: This check is safe even if the user switches
                 * from a legacy scrub to a sequential one in the middle
                 * of processing, since scn_is_sorted isn't updated until
                 * all outstanding IOs from the previous scrub pass
                 * complete.
                 */
                if ((zio->io_flags & ZIO_FLAG_SCRUB) &&
                    !(zio->io_flags & ZIO_FLAG_IO_RETRY) &&
                    dsl_scan_scrubbing(spa->spa_dsl_pool) &&
                    scn->scn_is_sorted) {
                        c = 1;
                } else {
                        c = BP_GET_NDVAS(zio->io_bp);
                }

                /*
                 * If we do not trust the pool config, some DVAs might be
                 * invalid or point to vdevs that do not exist. We skip them.
                 */
                if (!spa_trust_config(spa)) {
                        ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);
                        int j = 0;
                        for (int i = 0; i < c; i++) {
                                if (zfs_dva_valid(spa, &dva[i], zio->io_bp))
                                        dva_copy[j++] = dva[i];
                        }
                        if (j == 0) {
                                zio->io_vsd = NULL;
                                zio->io_error = ENXIO;
                                return (NULL);
                        }
                        if (j < c) {
                                dva = dva_copy;
                                c = j;
                        }
                }

                mm = vdev_mirror_map_alloc(c, B_FALSE, B_TRUE);
                for (c = 0; c < mm->mm_children; c++) {
                        mc = &mm->mm_child[c];

                        mc->mc_vd = vdev_lookup_top(spa, DVA_GET_VDEV(&dva[c]));
                        mc->mc_offset = DVA_GET_OFFSET(&dva[c]);
                }
        } else {
                /*
                 * If we are resilvering, then we should handle scrub reads
                 * differently; we shouldn't issue them to the resilvering
                 * device because it might not have those blocks.
                 *
                 * We are resilvering iff:
                 * 1) We are a replacing vdev (ie our name is "replacing-1" or
                 *    "spare-1" or something like that), and
                 * 2) The pool is currently being resilvered.
                 *
                 * We cannot simply check vd->vdev_resilver_txg, because it's
                 * not set in this path.
                 *
                 * Nor can we just check our vdev_ops; there are cases (such as
                 * when a user types "zpool replace pool odev spare_dev" and
                 * spare_dev is in the spare list, or when a spare device is
                 * automatically used to replace a DEGRADED device) when
                 * resilvering is complete but both the original vdev and the
                 * spare vdev remain in the pool.  That behavior is intentional.
                 * It helps implement the policy that a spare should be
                 * automatically removed from the pool after the user replaces
                 * the device that originally failed.
                 *
                 * If a spa load is in progress, then spa_dsl_pool may be
                 * uninitialized.  But we shouldn't be resilvering during a spa
                 * load anyway.
                 */
                boolean_t replacing = (vd->vdev_ops == &vdev_replacing_ops ||
                    vd->vdev_ops == &vdev_spare_ops) &&
                    spa_load_state(vd->vdev_spa) == SPA_LOAD_NONE &&
                    dsl_scan_resilvering(vd->vdev_spa->spa_dsl_pool);
                mm = vdev_mirror_map_alloc(vd->vdev_children, replacing,
                    B_FALSE);
                for (c = 0; c < mm->mm_children; c++) {
                        mc = &mm->mm_child[c];
                        mc->mc_vd = vd->vdev_child[c];
                        mc->mc_offset = zio->io_offset;
                }
        }

        zio->io_vsd = mm;
        zio->io_vsd_ops = &vdev_mirror_vsd_ops;
        return (mm);
}

static int
vdev_mirror_open(vdev_t *vd, uint64_t *asize, uint64_t *max_asize,
    uint64_t *ashift)
{
        int numerrors = 0;
        int lasterror = 0;

        if (vd->vdev_children == 0) {
                vd->vdev_stat.vs_aux = VDEV_AUX_BAD_LABEL;
                return (SET_ERROR(EINVAL));
        }

        vdev_open_children(vd);

        for (int c = 0; c < vd->vdev_children; c++) {
                vdev_t *cvd = vd->vdev_child[c];

                if (cvd->vdev_open_error) {
                        lasterror = cvd->vdev_open_error;
                        numerrors++;
                        continue;
                }

                *asize = MIN(*asize - 1, cvd->vdev_asize - 1) + 1;
                *max_asize = MIN(*max_asize - 1, cvd->vdev_max_asize - 1) + 1;
                *ashift = MAX(*ashift, cvd->vdev_ashift);
        }

        if (numerrors == vd->vdev_children) {
                if (vdev_children_are_offline(vd))
                        vd->vdev_stat.vs_aux = VDEV_AUX_CHILDREN_OFFLINE;
                else
                        vd->vdev_stat.vs_aux = VDEV_AUX_NO_REPLICAS;
                return (lasterror);
        }

        return (0);
}

static void
vdev_mirror_close(vdev_t *vd)
{
        for (int c = 0; c < vd->vdev_children; c++)
                vdev_close(vd->vdev_child[c]);
}

static void
vdev_mirror_child_done(zio_t *zio)
{
        mirror_child_t *mc = zio->io_private;

        mc->mc_error = zio->io_error;
        mc->mc_tried = 1;
        mc->mc_skipped = 0;
}

static void
vdev_mirror_scrub_done(zio_t *zio)
{
        mirror_child_t *mc = zio->io_private;

        if (zio->io_error == 0) {
                zio_t *pio;
                zio_link_t *zl = NULL;

                mutex_enter(&zio->io_lock);
                while ((pio = zio_walk_parents(zio, &zl)) != NULL) {
                        mutex_enter(&pio->io_lock);
                        ASSERT3U(zio->io_size, >=, pio->io_size);
                        abd_copy(pio->io_abd, zio->io_abd, pio->io_size);
                        mutex_exit(&pio->io_lock);
                }
                mutex_exit(&zio->io_lock);
        }

        abd_free(zio->io_abd);

        mc->mc_error = zio->io_error;
        mc->mc_tried = 1;
        mc->mc_skipped = 0;
}

/*
 * Check the other, lower-index DVAs to see if they're on the same
 * vdev as the child we picked.  If they are, use them since they
 * are likely to have been allocated from the primary metaslab in
 * use at the time, and hence are more likely to have locality with
 * single-copy data.
 */
static int
vdev_mirror_dva_select(zio_t *zio, int p)
{
        dva_t *dva = zio->io_bp->blk_dva;
        mirror_map_t *mm = zio->io_vsd;
        int preferred;
        int c;

        preferred = mm->mm_preferred[p];
        for (p--; p >= 0; p--) {
                c = mm->mm_preferred[p];
                if (DVA_GET_VDEV(&dva[c]) == DVA_GET_VDEV(&dva[preferred]))
                        preferred = c;
        }
        return (preferred);
}

static int
vdev_mirror_preferred_child_randomize(zio_t *zio)
{
        mirror_map_t *mm = zio->io_vsd;
        int p;

        if (mm->mm_root) {
                p = spa_get_random(mm->mm_preferred_cnt);
                return (vdev_mirror_dva_select(zio, p));
        }

        /*
         * To ensure we don't always favour the first matching vdev,
         * which could lead to wear leveling issues on SSD's, we
         * use the I/O offset as a pseudo random seed into the vdevs
         * which have the lowest load.
         */
        p = (zio->io_offset >> vdev_mirror_shift) % mm->mm_preferred_cnt;
        return (mm->mm_preferred[p]);
}

/*
 * Try to find a vdev whose DTL doesn't contain the block we want to read
 * preferring vdevs based on determined load.
 *
 * Try to find a child whose DTL doesn't contain the block we want to read.
 * If we can't, try the read on any vdev we haven't already tried.
 */
static int
vdev_mirror_child_select(zio_t *zio)
{
        mirror_map_t *mm = zio->io_vsd;
        uint64_t txg = zio->io_txg;
        int c, lowest_load;

        ASSERT(zio->io_bp == NULL || BP_PHYSICAL_BIRTH(zio->io_bp) == txg);

        lowest_load = INT_MAX;
        mm->mm_preferred_cnt = 0;
        for (c = 0; c < mm->mm_children; c++) {
                mirror_child_t *mc;

                mc = &mm->mm_child[c];
                if (mc->mc_tried || mc->mc_skipped)
                        continue;

                if (mc->mc_vd == NULL || !vdev_readable(mc->mc_vd)) {
                        mc->mc_error = SET_ERROR(ENXIO);
                        mc->mc_tried = 1;       /* don't even try */
                        mc->mc_skipped = 1;
                        continue;
                }

                if (vdev_dtl_contains(mc->mc_vd, DTL_MISSING, txg, 1)) {
                        mc->mc_error = SET_ERROR(ESTALE);
                        mc->mc_skipped = 1;
                        mc->mc_speculative = 1;
                        continue;
                }

                mc->mc_load = vdev_mirror_load(mm, mc->mc_vd, mc->mc_offset);
                if (mc->mc_load > lowest_load)
                        continue;

                if (mc->mc_load < lowest_load) {
                        lowest_load = mc->mc_load;
                        mm->mm_preferred_cnt = 0;
                }
                mm->mm_preferred[mm->mm_preferred_cnt] = c;
                mm->mm_preferred_cnt++;
        }

        if (mm->mm_preferred_cnt == 1) {
                MIRROR_BUMP(vdev_mirror_stat_preferred_found);
                return (mm->mm_preferred[0]);
        }

        if (mm->mm_preferred_cnt > 1) {
                MIRROR_BUMP(vdev_mirror_stat_preferred_not_found);
                return (vdev_mirror_preferred_child_randomize(zio));
        }

        /*
         * Every device is either missing or has this txg in its DTL.
         * Look for any child we haven't already tried before giving up.
         */
        for (c = 0; c < mm->mm_children; c++) {
                if (!mm->mm_child[c].mc_tried)
                        return (c);
        }

        /*
         * Every child failed.  There's no place left to look.
         */
        return (-1);
}

static void
vdev_mirror_io_start(zio_t *zio)
{
        mirror_map_t *mm;
        mirror_child_t *mc;
        int c, children;

        mm = vdev_mirror_map_init(zio);

        if (mm == NULL) {
                ASSERT(!spa_trust_config(zio->io_spa));
                ASSERT(zio->io_type == ZIO_TYPE_READ);
                zio_execute(zio);
                return;
        }

        if (zio->io_type == ZIO_TYPE_READ) {
                if (zio->io_bp != NULL &&
                    (zio->io_flags & ZIO_FLAG_SCRUB) && !mm->mm_resilvering) {
                        /*
                         * For scrubbing reads (if we can verify the
                         * checksum here, as indicated by io_bp being
                         * non-NULL) we need to allocate a read buffer for
                         * each child and issue reads to all children.  If
                         * any child succeeds, it will copy its data into
                         * zio->io_data in vdev_mirror_scrub_done.
                         */
                        for (c = 0; c < mm->mm_children; c++) {
                                mc = &mm->mm_child[c];
                                zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                                    mc->mc_vd, mc->mc_offset,
                                    abd_alloc_sametype(zio->io_abd,
                                    zio->io_size), zio->io_size,
                                    zio->io_type, zio->io_priority, 0,
                                    vdev_mirror_scrub_done, mc));
                        }
                        zio_execute(zio);
                        return;
                }
                /*
                 * For normal reads just pick one child.
                 */
                c = vdev_mirror_child_select(zio);
                children = (c >= 0);
        } else {
                ASSERT(zio->io_type == ZIO_TYPE_WRITE);

                /*
                 * Writes go to all children.
                 */
                c = 0;
                children = mm->mm_children;
        }

        while (children--) {
                mc = &mm->mm_child[c];
                zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                    mc->mc_vd, mc->mc_offset, zio->io_abd, zio->io_size,
                    zio->io_type, zio->io_priority, 0,
                    vdev_mirror_child_done, mc));
                c++;
        }

        zio_execute(zio);
}

static int
vdev_mirror_worst_error(mirror_map_t *mm)
{
        int error[2] = { 0, 0 };

        for (int c = 0; c < mm->mm_children; c++) {
                mirror_child_t *mc = &mm->mm_child[c];
                int s = mc->mc_speculative;
                error[s] = zio_worst_error(error[s], mc->mc_error);
        }

        return (error[0] ? error[0] : error[1]);
}

static void
vdev_mirror_io_done(zio_t *zio)
{
        mirror_map_t *mm = zio->io_vsd;
        mirror_child_t *mc;
        int c;
        int good_copies = 0;
        int unexpected_errors = 0;

        if (mm == NULL)
                return;

        for (c = 0; c < mm->mm_children; c++) {
                mc = &mm->mm_child[c];

                if (mc->mc_error) {
                        if (!mc->mc_skipped)
                                unexpected_errors++;
                } else if (mc->mc_tried) {
                        good_copies++;
                }
        }

        if (zio->io_type == ZIO_TYPE_WRITE) {
                /*
                 * XXX -- for now, treat partial writes as success.
                 *
                 * Now that we support write reallocation, it would be better
                 * to treat partial failure as real failure unless there are
                 * no non-degraded top-level vdevs left, and not update DTLs
                 * if we intend to reallocate.
                 */
                /* XXPOLICY */
                if (good_copies != mm->mm_children) {
                        /*
                         * Always require at least one good copy.
                         *
                         * For ditto blocks (io_vd == NULL), require
                         * all copies to be good.
                         *
                         * XXX -- for replacing vdevs, there's no great answer.
                         * If the old device is really dead, we may not even
                         * be able to access it -- so we only want to
                         * require good writes to the new device.  But if
                         * the new device turns out to be flaky, we want
                         * to be able to detach it -- which requires all
                         * writes to the old device to have succeeded.
                         */
                        if (good_copies == 0 || zio->io_vd == NULL)
                                zio->io_error = vdev_mirror_worst_error(mm);
                }
                return;
        }

        ASSERT(zio->io_type == ZIO_TYPE_READ);

        /*
         * If we don't have a good copy yet, keep trying other children.
         */
        /* XXPOLICY */
        if (good_copies == 0 && (c = vdev_mirror_child_select(zio)) != -1) {
                ASSERT(c >= 0 && c < mm->mm_children);
                mc = &mm->mm_child[c];
                zio_vdev_io_redone(zio);
                zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                    mc->mc_vd, mc->mc_offset, zio->io_abd, zio->io_size,
                    ZIO_TYPE_READ, zio->io_priority, 0,
                    vdev_mirror_child_done, mc));
                return;
        }

        /* XXPOLICY */
        if (good_copies == 0) {
                zio->io_error = vdev_mirror_worst_error(mm);
                ASSERT(zio->io_error != 0);
        }

        if (good_copies && spa_writeable(zio->io_spa) &&
            (unexpected_errors ||
            (zio->io_flags & ZIO_FLAG_RESILVER) ||
            ((zio->io_flags & ZIO_FLAG_SCRUB) && mm->mm_resilvering))) {
                /*
                 * Use the good data we have in hand to repair damaged children.
                 */
                for (c = 0; c < mm->mm_children; c++) {
                        /*
                         * Don't rewrite known good children.
                         * Not only is it unnecessary, it could
                         * actually be harmful: if the system lost
                         * power while rewriting the only good copy,
                         * there would be no good copies left!
                         */
                        mc = &mm->mm_child[c];

                        if (mc->mc_error == 0) {
                                if (mc->mc_tried)
                                        continue;
                                /*
                                 * We didn't try this child.  We need to
                                 * repair it if:
                                 * 1. it's a scrub (in which case we have
                                 * tried everything that was healthy)
                                 *  - or -
                                 * 2. it's an indirect vdev (in which case
                                 * it could point to any other vdev, which
                                 * might have a bad DTL)
                                 *  - or -
                                 * 3. the DTL indicates that this data is
                                 * missing from this vdev
                                 */
                                if (!(zio->io_flags & ZIO_FLAG_SCRUB) &&
                                    mc->mc_vd->vdev_ops != &vdev_indirect_ops &&
                                    !vdev_dtl_contains(mc->mc_vd, DTL_PARTIAL,
                                    zio->io_txg, 1))
                                        continue;
                                mc->mc_error = SET_ERROR(ESTALE);
                        }

                        zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                            mc->mc_vd, mc->mc_offset,
                            zio->io_abd, zio->io_size,
                            ZIO_TYPE_WRITE, ZIO_PRIORITY_ASYNC_WRITE,
                            ZIO_FLAG_IO_REPAIR | (unexpected_errors ?
                            ZIO_FLAG_SELF_HEAL : 0), NULL, NULL));
                }
        }
}

static void
vdev_mirror_state_change(vdev_t *vd, int faulted, int degraded)
{
        if (faulted == vd->vdev_children) {
                if (vdev_children_are_offline(vd)) {
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_OFFLINE,
                            VDEV_AUX_CHILDREN_OFFLINE);
                } else {
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_NO_REPLICAS);
                }
        } else if (degraded + faulted != 0) {
                vdev_set_state(vd, B_FALSE, VDEV_STATE_DEGRADED, VDEV_AUX_NONE);
        } else {
                vdev_set_state(vd, B_FALSE, VDEV_STATE_HEALTHY, VDEV_AUX_NONE);
        }
}

vdev_ops_t vdev_mirror_ops = {
        .vdev_op_open = vdev_mirror_open,
        .vdev_op_close = vdev_mirror_close,
        .vdev_op_asize = vdev_default_asize,
        .vdev_op_io_start = vdev_mirror_io_start,
        .vdev_op_io_done = vdev_mirror_io_done,
        .vdev_op_state_change = vdev_mirror_state_change,
        .vdev_op_need_resilver = NULL,
        .vdev_op_hold = NULL,
        .vdev_op_rele = NULL,
        .vdev_op_remap = NULL,
        .vdev_op_xlate = vdev_default_xlate,
        .vdev_op_type = VDEV_TYPE_MIRROR,       /* name of this vdev type */
        .vdev_op_leaf = B_FALSE                 /* not a leaf vdev */
};

vdev_ops_t vdev_replacing_ops = {
        .vdev_op_open = vdev_mirror_open,
        .vdev_op_close = vdev_mirror_close,
        .vdev_op_asize = vdev_default_asize,
        .vdev_op_io_start = vdev_mirror_io_start,
        .vdev_op_io_done = vdev_mirror_io_done,
        .vdev_op_state_change = vdev_mirror_state_change,
        .vdev_op_need_resilver = NULL,
        .vdev_op_hold = NULL,
        .vdev_op_rele = NULL,
        .vdev_op_remap = NULL,
        .vdev_op_xlate = vdev_default_xlate,
        .vdev_op_type = VDEV_TYPE_REPLACING,    /* name of this vdev type */
        .vdev_op_leaf = B_FALSE                 /* not a leaf vdev */
};

vdev_ops_t vdev_spare_ops = {
        .vdev_op_open = vdev_mirror_open,
        .vdev_op_close = vdev_mirror_close,
        .vdev_op_asize = vdev_default_asize,
        .vdev_op_io_start = vdev_mirror_io_start,
        .vdev_op_io_done = vdev_mirror_io_done,
        .vdev_op_state_change = vdev_mirror_state_change,
        .vdev_op_need_resilver = NULL,
        .vdev_op_hold = NULL,
        .vdev_op_rele = NULL,
        .vdev_op_remap = NULL,
        .vdev_op_xlate = vdev_default_xlate,
        .vdev_op_type = VDEV_TYPE_SPARE,        /* name of this vdev type */
        .vdev_op_leaf = B_FALSE                 /* not a leaf vdev */
};

#if defined(_KERNEL)
/* BEGIN CSTYLED */
module_param(zfs_vdev_mirror_rotating_inc, int, 0644);
MODULE_PARM_DESC(zfs_vdev_mirror_rotating_inc,
        "Rotating media load increment for non-seeking I/O's");

module_param(zfs_vdev_mirror_rotating_seek_inc, int, 0644);
MODULE_PARM_DESC(zfs_vdev_mirror_rotating_seek_inc,
        "Rotating media load increment for seeking I/O's");

module_param(zfs_vdev_mirror_rotating_seek_offset, int, 0644);

MODULE_PARM_DESC(zfs_vdev_mirror_rotating_seek_offset,
        "Offset in bytes from the last I/O which "
        "triggers a reduced rotating media seek increment");

module_param(zfs_vdev_mirror_non_rotating_inc, int, 0644);
MODULE_PARM_DESC(zfs_vdev_mirror_non_rotating_inc,
        "Non-rotating media load increment for non-seeking I/O's");

module_param(zfs_vdev_mirror_non_rotating_seek_inc, int, 0644);
MODULE_PARM_DESC(zfs_vdev_mirror_non_rotating_seek_inc,
        "Non-rotating media load increment for seeking I/O's");
/* END CSTYLED */
#endif