fs/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) 2013 by Delphix. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/vdev_impl.h>
#include <sys/zio.h>
#include <sys/fs/zfs.h>

/*
 * 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_replacing;
	boolean_t	mm_root;
	mirror_child_t	mm_child[];
} mirror_map_t;

static int vdev_mirror_shift = 21;

SYSCTL_DECL(_vfs_zfs_vdev);
static SYSCTL_NODE(_vfs_zfs_vdev, OID_AUTO, mirror, CTLFLAG_RD, 0,
    "ZFS VDEV Mirror");

/*
 * 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
 * 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 rotating_inc = 0;
SYSCTL_INT(_vfs_zfs_vdev_mirror, OID_AUTO, rotating_inc, CTLFLAG_RWTUN,
    &rotating_inc, 0, "Rotating media load increment for non-seeking I/O's");

static int rotating_seek_inc = 5;
SYSCTL_INT(_vfs_zfs_vdev_mirror, OID_AUTO, rotating_seek_inc, CTLFLAG_RWTUN,
    &rotating_seek_inc, 0, "Rotating media load increment for seeking I/O's");

static int rotating_seek_offset = 1 * 1024 * 1024;
SYSCTL_INT(_vfs_zfs_vdev_mirror, OID_AUTO, rotating_seek_offset, CTLFLAG_RWTUN,
    &rotating_seek_offset, 0, "Offset in bytes from the last I/O which "
    "triggers a reduced rotating media seek increment");

/* Non-rotating media load calculation configuration. */
static int non_rotating_inc = 0;
SYSCTL_INT(_vfs_zfs_vdev_mirror, OID_AUTO, non_rotating_inc, CTLFLAG_RWTUN,
    &non_rotating_inc, 0,
    "Non-rotating media load increment for non-seeking I/O's");

static int non_rotating_seek_inc = 1;
SYSCTL_INT(_vfs_zfs_vdev_mirror, OID_AUTO, non_rotating_seek_inc, CTLFLAG_RWTUN,
    &non_rotating_seek_inc, 0,
    "Non-rotating media load increment for seeking I/O's");


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 replacing, boolean_t root)
{
	mirror_map_t *mm;

	mm = kmem_zalloc(vdev_mirror_map_size(children), KM_SLEEP);
	mm->mm_children = children;
	mm->mm_replacing = replacing;
	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 = {
	vdev_mirror_map_free,
	zio_vsd_default_cksum_report
};

static int
vdev_mirror_load(mirror_map_t *mm, vdev_t *vd, uint64_t zio_offset)
{
	uint64_t lastoffset;
	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.
	 */

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

	if (vd->vdev_rotation_rate == VDEV_RATE_NON_ROTATING) {
		/* Non-rotating media. */
		if (lastoffset == zio_offset)
			return (load + non_rotating_inc);

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

	/* Rotating media I/O's which directly follow the last I/O. */
	if (lastoffset == zio_offset)
		return (load + rotating_inc);

	/*
	 * Apply half the seek increment to I/O's within seek offset
	 * of the last I/O queued to this vdev as they should incure less
	 * of a seek increment.
	 */
	if (ABS(lastoffset - zio_offset) < rotating_seek_offset)
		return (load + (rotating_seek_inc / 2));

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


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;

		mm = vdev_mirror_map_alloc(BP_GET_NDVAS(zio->io_bp), 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 {
		mm = vdev_mirror_map_alloc(vd->vdev_children,
		    (vd->vdev_ops == &vdev_replacing_ops ||
                    vd->vdev_ops == &vdev_spare_ops), 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 *logical_ashift, uint64_t *physical_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;
		*logical_ashift = MAX(*logical_ashift, cvd->vdev_ashift);
		*physical_ashift = MAX(*physical_ashift,
		    cvd->vdev_physical_ashift);
	}

	if (numerrors == vd->vdev_children) {
		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;

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

	zio_buf_free(zio->io_data, zio->io_size);

	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
 * prefering vdevs based on determined load.
 *
 * 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 (!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) {
		vdev_queue_register_lastoffset(
		    mm->mm_child[mm->mm_preferred[0]].mc_vd, zio);
		return (mm->mm_preferred[0]);
	}

	if (mm->mm_preferred_cnt > 1) {
		int c = vdev_mirror_preferred_child_randomize(zio);

		vdev_queue_register_lastoffset(mm->mm_child[c].mc_vd, zio);
		return (c);
	}

	/*
	 * 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) {
			vdev_queue_register_lastoffset(mm->mm_child[c].mc_vd,
			    zio);
			return (c);
		}
	}

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

static int
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 (zio->io_type == ZIO_TYPE_READ) {
		if ((zio->io_flags & ZIO_FLAG_SCRUB) && !mm->mm_replacing) {
			/*
			 * For scrubbing reads 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,
				    zio_buf_alloc(zio->io_size), zio->io_size,
				    zio->io_type, zio->io_priority, 0,
				    vdev_mirror_scrub_done, mc));
			}
			zio_interrupt(zio);
			return (ZIO_PIPELINE_STOP);
		}
		/*
		 * For normal reads just pick one child.
		 */
		c = vdev_mirror_child_select(zio);
		children = (c >= 0);
	} else {
		ASSERT(zio->io_type == ZIO_TYPE_WRITE ||
		    zio->io_type == ZIO_TYPE_FREE);

		/*
		 * Writes and frees 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_data, zio->io_size,
		    zio->io_type, zio->io_priority, 0,
		    vdev_mirror_child_done, mc));
		c++;
	}

	zio_interrupt(zio);
	return (ZIO_PIPELINE_STOP);
}

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;

	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;
	} else if (zio->io_type == ZIO_TYPE_FREE) {
		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_data, 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_replacing))) {
		/*
		 * 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;
				if (!(zio->io_flags & ZIO_FLAG_SCRUB) &&
				    !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_data, 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)
		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_mirror_open,
	vdev_mirror_close,
	vdev_default_asize,
	vdev_mirror_io_start,
	vdev_mirror_io_done,
	vdev_mirror_state_change,
	NULL,
	NULL,
	VDEV_TYPE_MIRROR,	/* name of this vdev type */
	B_FALSE			/* not a leaf vdev */
};

vdev_ops_t vdev_replacing_ops = {
	vdev_mirror_open,
	vdev_mirror_close,
	vdev_default_asize,
	vdev_mirror_io_start,
	vdev_mirror_io_done,
	vdev_mirror_state_change,
	NULL,
	NULL,
	VDEV_TYPE_REPLACING,	/* name of this vdev type */
	B_FALSE			/* not a leaf vdev */
};

vdev_ops_t vdev_spare_ops = {
	vdev_mirror_open,
	vdev_mirror_close,
	vdev_default_asize,
	vdev_mirror_io_start,
	vdev_mirror_io_done,
	vdev_mirror_state_change,
	NULL,
	NULL,
	VDEV_TYPE_SPARE,	/* name of this vdev type */
	B_FALSE			/* not a leaf vdev */
};