xref: /freebsd/sys/contrib/openzfs/module/zfs/vdev_mirror.c (revision 2eb4d8dc723da3cf7d735a3226ae49da4c8c5dbc)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
23  * Use is subject to license terms.
24  */
25 
26 /*
27  * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
28  */
29 
30 #include <sys/zfs_context.h>
31 #include <sys/spa.h>
32 #include <sys/spa_impl.h>
33 #include <sys/dsl_pool.h>
34 #include <sys/dsl_scan.h>
35 #include <sys/vdev_impl.h>
36 #include <sys/vdev_draid.h>
37 #include <sys/zio.h>
38 #include <sys/abd.h>
39 #include <sys/fs/zfs.h>
40 
41 /*
42  * Vdev mirror kstats
43  */
44 static kstat_t *mirror_ksp = NULL;
45 
46 typedef struct mirror_stats {
47 	kstat_named_t vdev_mirror_stat_rotating_linear;
48 	kstat_named_t vdev_mirror_stat_rotating_offset;
49 	kstat_named_t vdev_mirror_stat_rotating_seek;
50 	kstat_named_t vdev_mirror_stat_non_rotating_linear;
51 	kstat_named_t vdev_mirror_stat_non_rotating_seek;
52 
53 	kstat_named_t vdev_mirror_stat_preferred_found;
54 	kstat_named_t vdev_mirror_stat_preferred_not_found;
55 } mirror_stats_t;
56 
57 static mirror_stats_t mirror_stats = {
58 	/* New I/O follows directly the last I/O */
59 	{ "rotating_linear",			KSTAT_DATA_UINT64 },
60 	/* New I/O is within zfs_vdev_mirror_rotating_seek_offset of the last */
61 	{ "rotating_offset",			KSTAT_DATA_UINT64 },
62 	/* New I/O requires random seek */
63 	{ "rotating_seek",			KSTAT_DATA_UINT64 },
64 	/* New I/O follows directly the last I/O  (nonrot) */
65 	{ "non_rotating_linear",		KSTAT_DATA_UINT64 },
66 	/* New I/O requires random seek (nonrot) */
67 	{ "non_rotating_seek",			KSTAT_DATA_UINT64 },
68 	/* Preferred child vdev found */
69 	{ "preferred_found",			KSTAT_DATA_UINT64 },
70 	/* Preferred child vdev not found or equal load  */
71 	{ "preferred_not_found",		KSTAT_DATA_UINT64 },
72 
73 };
74 
75 #define	MIRROR_STAT(stat)		(mirror_stats.stat.value.ui64)
76 #define	MIRROR_INCR(stat, val) 		atomic_add_64(&MIRROR_STAT(stat), val)
77 #define	MIRROR_BUMP(stat)		MIRROR_INCR(stat, 1)
78 
79 void
80 vdev_mirror_stat_init(void)
81 {
82 	mirror_ksp = kstat_create("zfs", 0, "vdev_mirror_stats",
83 	    "misc", KSTAT_TYPE_NAMED,
84 	    sizeof (mirror_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
85 	if (mirror_ksp != NULL) {
86 		mirror_ksp->ks_data = &mirror_stats;
87 		kstat_install(mirror_ksp);
88 	}
89 }
90 
91 void
92 vdev_mirror_stat_fini(void)
93 {
94 	if (mirror_ksp != NULL) {
95 		kstat_delete(mirror_ksp);
96 		mirror_ksp = NULL;
97 	}
98 }
99 
100 /*
101  * Virtual device vector for mirroring.
102  */
103 typedef struct mirror_child {
104 	vdev_t		*mc_vd;
105 	uint64_t	mc_offset;
106 	int		mc_error;
107 	int		mc_load;
108 	uint8_t		mc_tried;
109 	uint8_t		mc_skipped;
110 	uint8_t		mc_speculative;
111 	uint8_t		mc_rebuilding;
112 } mirror_child_t;
113 
114 typedef struct mirror_map {
115 	int		*mm_preferred;
116 	int		mm_preferred_cnt;
117 	int		mm_children;
118 	boolean_t	mm_resilvering;
119 	boolean_t	mm_rebuilding;
120 	boolean_t	mm_root;
121 	mirror_child_t	mm_child[];
122 } mirror_map_t;
123 
124 static int vdev_mirror_shift = 21;
125 
126 /*
127  * The load configuration settings below are tuned by default for
128  * the case where all devices are of the same rotational type.
129  *
130  * If there is a mixture of rotating and non-rotating media, setting
131  * zfs_vdev_mirror_non_rotating_seek_inc to 0 may well provide better results
132  * as it will direct more reads to the non-rotating vdevs which are more likely
133  * to have a higher performance.
134  */
135 
136 /* Rotating media load calculation configuration. */
137 static int zfs_vdev_mirror_rotating_inc = 0;
138 static int zfs_vdev_mirror_rotating_seek_inc = 5;
139 static int zfs_vdev_mirror_rotating_seek_offset = 1 * 1024 * 1024;
140 
141 /* Non-rotating media load calculation configuration. */
142 static int zfs_vdev_mirror_non_rotating_inc = 0;
143 static int zfs_vdev_mirror_non_rotating_seek_inc = 1;
144 
145 static inline size_t
146 vdev_mirror_map_size(int children)
147 {
148 	return (offsetof(mirror_map_t, mm_child[children]) +
149 	    sizeof (int) * children);
150 }
151 
152 static inline mirror_map_t *
153 vdev_mirror_map_alloc(int children, boolean_t resilvering, boolean_t root)
154 {
155 	mirror_map_t *mm;
156 
157 	mm = kmem_zalloc(vdev_mirror_map_size(children), KM_SLEEP);
158 	mm->mm_children = children;
159 	mm->mm_resilvering = resilvering;
160 	mm->mm_root = root;
161 	mm->mm_preferred = (int *)((uintptr_t)mm +
162 	    offsetof(mirror_map_t, mm_child[children]));
163 
164 	return (mm);
165 }
166 
167 static void
168 vdev_mirror_map_free(zio_t *zio)
169 {
170 	mirror_map_t *mm = zio->io_vsd;
171 
172 	kmem_free(mm, vdev_mirror_map_size(mm->mm_children));
173 }
174 
175 static const zio_vsd_ops_t vdev_mirror_vsd_ops = {
176 	.vsd_free = vdev_mirror_map_free,
177 };
178 
179 static int
180 vdev_mirror_load(mirror_map_t *mm, vdev_t *vd, uint64_t zio_offset)
181 {
182 	uint64_t last_offset;
183 	int64_t offset_diff;
184 	int load;
185 
186 	/* All DVAs have equal weight at the root. */
187 	if (mm->mm_root)
188 		return (INT_MAX);
189 
190 	/*
191 	 * We don't return INT_MAX if the device is resilvering i.e.
192 	 * vdev_resilver_txg != 0 as when tested performance was slightly
193 	 * worse overall when resilvering with compared to without.
194 	 */
195 
196 	/* Fix zio_offset for leaf vdevs */
197 	if (vd->vdev_ops->vdev_op_leaf)
198 		zio_offset += VDEV_LABEL_START_SIZE;
199 
200 	/* Standard load based on pending queue length. */
201 	load = vdev_queue_length(vd);
202 	last_offset = vdev_queue_last_offset(vd);
203 
204 	if (vd->vdev_nonrot) {
205 		/* Non-rotating media. */
206 		if (last_offset == zio_offset) {
207 			MIRROR_BUMP(vdev_mirror_stat_non_rotating_linear);
208 			return (load + zfs_vdev_mirror_non_rotating_inc);
209 		}
210 
211 		/*
212 		 * Apply a seek penalty even for non-rotating devices as
213 		 * sequential I/O's can be aggregated into fewer operations on
214 		 * the device, thus avoiding unnecessary per-command overhead
215 		 * and boosting performance.
216 		 */
217 		MIRROR_BUMP(vdev_mirror_stat_non_rotating_seek);
218 		return (load + zfs_vdev_mirror_non_rotating_seek_inc);
219 	}
220 
221 	/* Rotating media I/O's which directly follow the last I/O. */
222 	if (last_offset == zio_offset) {
223 		MIRROR_BUMP(vdev_mirror_stat_rotating_linear);
224 		return (load + zfs_vdev_mirror_rotating_inc);
225 	}
226 
227 	/*
228 	 * Apply half the seek increment to I/O's within seek offset
229 	 * of the last I/O issued to this vdev as they should incur less
230 	 * of a seek increment.
231 	 */
232 	offset_diff = (int64_t)(last_offset - zio_offset);
233 	if (ABS(offset_diff) < zfs_vdev_mirror_rotating_seek_offset) {
234 		MIRROR_BUMP(vdev_mirror_stat_rotating_offset);
235 		return (load + (zfs_vdev_mirror_rotating_seek_inc / 2));
236 	}
237 
238 	/* Apply the full seek increment to all other I/O's. */
239 	MIRROR_BUMP(vdev_mirror_stat_rotating_seek);
240 	return (load + zfs_vdev_mirror_rotating_seek_inc);
241 }
242 
243 static boolean_t
244 vdev_mirror_rebuilding(vdev_t *vd)
245 {
246 	if (vd->vdev_ops->vdev_op_leaf && vd->vdev_rebuild_txg)
247 		return (B_TRUE);
248 
249 	for (int i = 0; i < vd->vdev_children; i++) {
250 		if (vdev_mirror_rebuilding(vd->vdev_child[i])) {
251 			return (B_TRUE);
252 		}
253 	}
254 
255 	return (B_FALSE);
256 }
257 
258 /*
259  * Avoid inlining the function to keep vdev_mirror_io_start(), which
260  * is this functions only caller, as small as possible on the stack.
261  */
262 noinline static mirror_map_t *
263 vdev_mirror_map_init(zio_t *zio)
264 {
265 	mirror_map_t *mm = NULL;
266 	mirror_child_t *mc;
267 	vdev_t *vd = zio->io_vd;
268 	int c;
269 
270 	if (vd == NULL) {
271 		dva_t *dva = zio->io_bp->blk_dva;
272 		spa_t *spa = zio->io_spa;
273 		dsl_scan_t *scn = spa->spa_dsl_pool->dp_scan;
274 		dva_t dva_copy[SPA_DVAS_PER_BP];
275 
276 		/*
277 		 * The sequential scrub code sorts and issues all DVAs
278 		 * of a bp separately. Each of these IOs includes all
279 		 * original DVA copies so that repairs can be performed
280 		 * in the event of an error, but we only actually want
281 		 * to check the first DVA since the others will be
282 		 * checked by their respective sorted IOs. Only if we
283 		 * hit an error will we try all DVAs upon retrying.
284 		 *
285 		 * Note: This check is safe even if the user switches
286 		 * from a legacy scrub to a sequential one in the middle
287 		 * of processing, since scn_is_sorted isn't updated until
288 		 * all outstanding IOs from the previous scrub pass
289 		 * complete.
290 		 */
291 		if ((zio->io_flags & ZIO_FLAG_SCRUB) &&
292 		    !(zio->io_flags & ZIO_FLAG_IO_RETRY) &&
293 		    dsl_scan_scrubbing(spa->spa_dsl_pool) &&
294 		    scn->scn_is_sorted) {
295 			c = 1;
296 		} else {
297 			c = BP_GET_NDVAS(zio->io_bp);
298 		}
299 
300 		/*
301 		 * If the pool cannot be written to, then infer that some
302 		 * DVAs might be invalid or point to vdevs that do not exist.
303 		 * We skip them.
304 		 */
305 		if (!spa_writeable(spa)) {
306 			ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);
307 			int j = 0;
308 			for (int i = 0; i < c; i++) {
309 				if (zfs_dva_valid(spa, &dva[i], zio->io_bp))
310 					dva_copy[j++] = dva[i];
311 			}
312 			if (j == 0) {
313 				zio->io_vsd = NULL;
314 				zio->io_error = ENXIO;
315 				return (NULL);
316 			}
317 			if (j < c) {
318 				dva = dva_copy;
319 				c = j;
320 			}
321 		}
322 
323 		mm = vdev_mirror_map_alloc(c, B_FALSE, B_TRUE);
324 		for (c = 0; c < mm->mm_children; c++) {
325 			mc = &mm->mm_child[c];
326 
327 			mc->mc_vd = vdev_lookup_top(spa, DVA_GET_VDEV(&dva[c]));
328 			mc->mc_offset = DVA_GET_OFFSET(&dva[c]);
329 			if (mc->mc_vd == NULL) {
330 				kmem_free(mm, vdev_mirror_map_size(
331 				    mm->mm_children));
332 				zio->io_vsd = NULL;
333 				zio->io_error = ENXIO;
334 				return (NULL);
335 			}
336 		}
337 	} else {
338 		/*
339 		 * If we are resilvering, then we should handle scrub reads
340 		 * differently; we shouldn't issue them to the resilvering
341 		 * device because it might not have those blocks.
342 		 *
343 		 * We are resilvering iff:
344 		 * 1) We are a replacing vdev (ie our name is "replacing-1" or
345 		 *    "spare-1" or something like that), and
346 		 * 2) The pool is currently being resilvered.
347 		 *
348 		 * We cannot simply check vd->vdev_resilver_txg, because it's
349 		 * not set in this path.
350 		 *
351 		 * Nor can we just check our vdev_ops; there are cases (such as
352 		 * when a user types "zpool replace pool odev spare_dev" and
353 		 * spare_dev is in the spare list, or when a spare device is
354 		 * automatically used to replace a DEGRADED device) when
355 		 * resilvering is complete but both the original vdev and the
356 		 * spare vdev remain in the pool.  That behavior is intentional.
357 		 * It helps implement the policy that a spare should be
358 		 * automatically removed from the pool after the user replaces
359 		 * the device that originally failed.
360 		 *
361 		 * If a spa load is in progress, then spa_dsl_pool may be
362 		 * uninitialized.  But we shouldn't be resilvering during a spa
363 		 * load anyway.
364 		 */
365 		boolean_t replacing = (vd->vdev_ops == &vdev_replacing_ops ||
366 		    vd->vdev_ops == &vdev_spare_ops) &&
367 		    spa_load_state(vd->vdev_spa) == SPA_LOAD_NONE &&
368 		    dsl_scan_resilvering(vd->vdev_spa->spa_dsl_pool);
369 		mm = vdev_mirror_map_alloc(vd->vdev_children, replacing,
370 		    B_FALSE);
371 		for (c = 0; c < mm->mm_children; c++) {
372 			mc = &mm->mm_child[c];
373 			mc->mc_vd = vd->vdev_child[c];
374 			mc->mc_offset = zio->io_offset;
375 
376 			if (vdev_mirror_rebuilding(mc->mc_vd))
377 				mm->mm_rebuilding = mc->mc_rebuilding = B_TRUE;
378 		}
379 	}
380 
381 	return (mm);
382 }
383 
384 static int
385 vdev_mirror_open(vdev_t *vd, uint64_t *asize, uint64_t *max_asize,
386     uint64_t *logical_ashift, uint64_t *physical_ashift)
387 {
388 	int numerrors = 0;
389 	int lasterror = 0;
390 
391 	if (vd->vdev_children == 0) {
392 		vd->vdev_stat.vs_aux = VDEV_AUX_BAD_LABEL;
393 		return (SET_ERROR(EINVAL));
394 	}
395 
396 	vdev_open_children(vd);
397 
398 	for (int c = 0; c < vd->vdev_children; c++) {
399 		vdev_t *cvd = vd->vdev_child[c];
400 
401 		if (cvd->vdev_open_error) {
402 			lasterror = cvd->vdev_open_error;
403 			numerrors++;
404 			continue;
405 		}
406 
407 		*asize = MIN(*asize - 1, cvd->vdev_asize - 1) + 1;
408 		*max_asize = MIN(*max_asize - 1, cvd->vdev_max_asize - 1) + 1;
409 		*logical_ashift = MAX(*logical_ashift, cvd->vdev_ashift);
410 		*physical_ashift = MAX(*physical_ashift,
411 		    cvd->vdev_physical_ashift);
412 	}
413 
414 	if (numerrors == vd->vdev_children) {
415 		if (vdev_children_are_offline(vd))
416 			vd->vdev_stat.vs_aux = VDEV_AUX_CHILDREN_OFFLINE;
417 		else
418 			vd->vdev_stat.vs_aux = VDEV_AUX_NO_REPLICAS;
419 		return (lasterror);
420 	}
421 
422 	return (0);
423 }
424 
425 static void
426 vdev_mirror_close(vdev_t *vd)
427 {
428 	for (int c = 0; c < vd->vdev_children; c++)
429 		vdev_close(vd->vdev_child[c]);
430 }
431 
432 static void
433 vdev_mirror_child_done(zio_t *zio)
434 {
435 	mirror_child_t *mc = zio->io_private;
436 
437 	mc->mc_error = zio->io_error;
438 	mc->mc_tried = 1;
439 	mc->mc_skipped = 0;
440 }
441 
442 static void
443 vdev_mirror_scrub_done(zio_t *zio)
444 {
445 	mirror_child_t *mc = zio->io_private;
446 
447 	if (zio->io_error == 0) {
448 		zio_t *pio;
449 		zio_link_t *zl = NULL;
450 
451 		mutex_enter(&zio->io_lock);
452 		while ((pio = zio_walk_parents(zio, &zl)) != NULL) {
453 			mutex_enter(&pio->io_lock);
454 			ASSERT3U(zio->io_size, >=, pio->io_size);
455 			abd_copy(pio->io_abd, zio->io_abd, pio->io_size);
456 			mutex_exit(&pio->io_lock);
457 		}
458 		mutex_exit(&zio->io_lock);
459 	}
460 
461 	abd_free(zio->io_abd);
462 
463 	mc->mc_error = zio->io_error;
464 	mc->mc_tried = 1;
465 	mc->mc_skipped = 0;
466 }
467 
468 /*
469  * Check the other, lower-index DVAs to see if they're on the same
470  * vdev as the child we picked.  If they are, use them since they
471  * are likely to have been allocated from the primary metaslab in
472  * use at the time, and hence are more likely to have locality with
473  * single-copy data.
474  */
475 static int
476 vdev_mirror_dva_select(zio_t *zio, int p)
477 {
478 	dva_t *dva = zio->io_bp->blk_dva;
479 	mirror_map_t *mm = zio->io_vsd;
480 	int preferred;
481 	int c;
482 
483 	preferred = mm->mm_preferred[p];
484 	for (p--; p >= 0; p--) {
485 		c = mm->mm_preferred[p];
486 		if (DVA_GET_VDEV(&dva[c]) == DVA_GET_VDEV(&dva[preferred]))
487 			preferred = c;
488 	}
489 	return (preferred);
490 }
491 
492 static int
493 vdev_mirror_preferred_child_randomize(zio_t *zio)
494 {
495 	mirror_map_t *mm = zio->io_vsd;
496 	int p;
497 
498 	if (mm->mm_root) {
499 		p = random_in_range(mm->mm_preferred_cnt);
500 		return (vdev_mirror_dva_select(zio, p));
501 	}
502 
503 	/*
504 	 * To ensure we don't always favour the first matching vdev,
505 	 * which could lead to wear leveling issues on SSD's, we
506 	 * use the I/O offset as a pseudo random seed into the vdevs
507 	 * which have the lowest load.
508 	 */
509 	p = (zio->io_offset >> vdev_mirror_shift) % mm->mm_preferred_cnt;
510 	return (mm->mm_preferred[p]);
511 }
512 
513 static boolean_t
514 vdev_mirror_child_readable(mirror_child_t *mc)
515 {
516 	vdev_t *vd = mc->mc_vd;
517 
518 	if (vd->vdev_top != NULL && vd->vdev_top->vdev_ops == &vdev_draid_ops)
519 		return (vdev_draid_readable(vd, mc->mc_offset));
520 	else
521 		return (vdev_readable(vd));
522 }
523 
524 static boolean_t
525 vdev_mirror_child_missing(mirror_child_t *mc, uint64_t txg, uint64_t size)
526 {
527 	vdev_t *vd = mc->mc_vd;
528 
529 	if (vd->vdev_top != NULL && vd->vdev_top->vdev_ops == &vdev_draid_ops)
530 		return (vdev_draid_missing(vd, mc->mc_offset, txg, size));
531 	else
532 		return (vdev_dtl_contains(vd, DTL_MISSING, txg, size));
533 }
534 
535 /*
536  * Try to find a vdev whose DTL doesn't contain the block we want to read
537  * preferring vdevs based on determined load. If we can't, try the read on
538  * any vdev we haven't already tried.
539  *
540  * Distributed spares are an exception to the above load rule. They are
541  * always preferred in order to detect gaps in the distributed spare which
542  * are created when another disk in the dRAID fails. In order to restore
543  * redundancy those gaps must be read to trigger the required repair IO.
544  */
545 static int
546 vdev_mirror_child_select(zio_t *zio)
547 {
548 	mirror_map_t *mm = zio->io_vsd;
549 	uint64_t txg = zio->io_txg;
550 	int c, lowest_load;
551 
552 	ASSERT(zio->io_bp == NULL || BP_PHYSICAL_BIRTH(zio->io_bp) == txg);
553 
554 	lowest_load = INT_MAX;
555 	mm->mm_preferred_cnt = 0;
556 	for (c = 0; c < mm->mm_children; c++) {
557 		mirror_child_t *mc;
558 
559 		mc = &mm->mm_child[c];
560 		if (mc->mc_tried || mc->mc_skipped)
561 			continue;
562 
563 		if (mc->mc_vd == NULL ||
564 		    !vdev_mirror_child_readable(mc)) {
565 			mc->mc_error = SET_ERROR(ENXIO);
566 			mc->mc_tried = 1;	/* don't even try */
567 			mc->mc_skipped = 1;
568 			continue;
569 		}
570 
571 		if (vdev_mirror_child_missing(mc, txg, 1)) {
572 			mc->mc_error = SET_ERROR(ESTALE);
573 			mc->mc_skipped = 1;
574 			mc->mc_speculative = 1;
575 			continue;
576 		}
577 
578 		if (mc->mc_vd->vdev_ops == &vdev_draid_spare_ops) {
579 			mm->mm_preferred[0] = c;
580 			mm->mm_preferred_cnt = 1;
581 			break;
582 		}
583 
584 		mc->mc_load = vdev_mirror_load(mm, mc->mc_vd, mc->mc_offset);
585 		if (mc->mc_load > lowest_load)
586 			continue;
587 
588 		if (mc->mc_load < lowest_load) {
589 			lowest_load = mc->mc_load;
590 			mm->mm_preferred_cnt = 0;
591 		}
592 		mm->mm_preferred[mm->mm_preferred_cnt] = c;
593 		mm->mm_preferred_cnt++;
594 	}
595 
596 	if (mm->mm_preferred_cnt == 1) {
597 		MIRROR_BUMP(vdev_mirror_stat_preferred_found);
598 		return (mm->mm_preferred[0]);
599 	}
600 
601 	if (mm->mm_preferred_cnt > 1) {
602 		MIRROR_BUMP(vdev_mirror_stat_preferred_not_found);
603 		return (vdev_mirror_preferred_child_randomize(zio));
604 	}
605 
606 	/*
607 	 * Every device is either missing or has this txg in its DTL.
608 	 * Look for any child we haven't already tried before giving up.
609 	 */
610 	for (c = 0; c < mm->mm_children; c++) {
611 		if (!mm->mm_child[c].mc_tried)
612 			return (c);
613 	}
614 
615 	/*
616 	 * Every child failed.  There's no place left to look.
617 	 */
618 	return (-1);
619 }
620 
621 static void
622 vdev_mirror_io_start(zio_t *zio)
623 {
624 	mirror_map_t *mm;
625 	mirror_child_t *mc;
626 	int c, children;
627 
628 	mm = vdev_mirror_map_init(zio);
629 	zio->io_vsd = mm;
630 	zio->io_vsd_ops = &vdev_mirror_vsd_ops;
631 
632 	if (mm == NULL) {
633 		ASSERT(!spa_trust_config(zio->io_spa));
634 		ASSERT(zio->io_type == ZIO_TYPE_READ);
635 		zio_execute(zio);
636 		return;
637 	}
638 
639 	if (zio->io_type == ZIO_TYPE_READ) {
640 		if (zio->io_bp != NULL &&
641 		    (zio->io_flags & ZIO_FLAG_SCRUB) && !mm->mm_resilvering) {
642 			/*
643 			 * For scrubbing reads (if we can verify the
644 			 * checksum here, as indicated by io_bp being
645 			 * non-NULL) we need to allocate a read buffer for
646 			 * each child and issue reads to all children.  If
647 			 * any child succeeds, it will copy its data into
648 			 * zio->io_data in vdev_mirror_scrub_done.
649 			 */
650 			for (c = 0; c < mm->mm_children; c++) {
651 				mc = &mm->mm_child[c];
652 
653 				/* Don't issue ZIOs to offline children */
654 				if (!vdev_mirror_child_readable(mc)) {
655 					mc->mc_error = SET_ERROR(ENXIO);
656 					mc->mc_tried = 1;
657 					mc->mc_skipped = 1;
658 					continue;
659 				}
660 
661 				zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
662 				    mc->mc_vd, mc->mc_offset,
663 				    abd_alloc_sametype(zio->io_abd,
664 				    zio->io_size), zio->io_size,
665 				    zio->io_type, zio->io_priority, 0,
666 				    vdev_mirror_scrub_done, mc));
667 			}
668 			zio_execute(zio);
669 			return;
670 		}
671 		/*
672 		 * For normal reads just pick one child.
673 		 */
674 		c = vdev_mirror_child_select(zio);
675 		children = (c >= 0);
676 	} else {
677 		ASSERT(zio->io_type == ZIO_TYPE_WRITE);
678 
679 		/*
680 		 * Writes go to all children.
681 		 */
682 		c = 0;
683 		children = mm->mm_children;
684 	}
685 
686 	while (children--) {
687 		mc = &mm->mm_child[c];
688 		c++;
689 
690 		/*
691 		 * When sequentially resilvering only issue write repair
692 		 * IOs to the vdev which is being rebuilt since performance
693 		 * is limited by the slowest child.  This is an issue for
694 		 * faster replacement devices such as distributed spares.
695 		 */
696 		if ((zio->io_priority == ZIO_PRIORITY_REBUILD) &&
697 		    (zio->io_flags & ZIO_FLAG_IO_REPAIR) &&
698 		    !(zio->io_flags & ZIO_FLAG_SCRUB) &&
699 		    mm->mm_rebuilding && !mc->mc_rebuilding) {
700 			continue;
701 		}
702 
703 		zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
704 		    mc->mc_vd, mc->mc_offset, zio->io_abd, zio->io_size,
705 		    zio->io_type, zio->io_priority, 0,
706 		    vdev_mirror_child_done, mc));
707 	}
708 
709 	zio_execute(zio);
710 }
711 
712 static int
713 vdev_mirror_worst_error(mirror_map_t *mm)
714 {
715 	int error[2] = { 0, 0 };
716 
717 	for (int c = 0; c < mm->mm_children; c++) {
718 		mirror_child_t *mc = &mm->mm_child[c];
719 		int s = mc->mc_speculative;
720 		error[s] = zio_worst_error(error[s], mc->mc_error);
721 	}
722 
723 	return (error[0] ? error[0] : error[1]);
724 }
725 
726 static void
727 vdev_mirror_io_done(zio_t *zio)
728 {
729 	mirror_map_t *mm = zio->io_vsd;
730 	mirror_child_t *mc;
731 	int c;
732 	int good_copies = 0;
733 	int unexpected_errors = 0;
734 
735 	if (mm == NULL)
736 		return;
737 
738 	for (c = 0; c < mm->mm_children; c++) {
739 		mc = &mm->mm_child[c];
740 
741 		if (mc->mc_error) {
742 			if (!mc->mc_skipped)
743 				unexpected_errors++;
744 		} else if (mc->mc_tried) {
745 			good_copies++;
746 		}
747 	}
748 
749 	if (zio->io_type == ZIO_TYPE_WRITE) {
750 		/*
751 		 * XXX -- for now, treat partial writes as success.
752 		 *
753 		 * Now that we support write reallocation, it would be better
754 		 * to treat partial failure as real failure unless there are
755 		 * no non-degraded top-level vdevs left, and not update DTLs
756 		 * if we intend to reallocate.
757 		 */
758 		/* XXPOLICY */
759 		if (good_copies != mm->mm_children) {
760 			/*
761 			 * Always require at least one good copy.
762 			 *
763 			 * For ditto blocks (io_vd == NULL), require
764 			 * all copies to be good.
765 			 *
766 			 * XXX -- for replacing vdevs, there's no great answer.
767 			 * If the old device is really dead, we may not even
768 			 * be able to access it -- so we only want to
769 			 * require good writes to the new device.  But if
770 			 * the new device turns out to be flaky, we want
771 			 * to be able to detach it -- which requires all
772 			 * writes to the old device to have succeeded.
773 			 */
774 			if (good_copies == 0 || zio->io_vd == NULL)
775 				zio->io_error = vdev_mirror_worst_error(mm);
776 		}
777 		return;
778 	}
779 
780 	ASSERT(zio->io_type == ZIO_TYPE_READ);
781 
782 	/*
783 	 * If we don't have a good copy yet, keep trying other children.
784 	 */
785 	/* XXPOLICY */
786 	if (good_copies == 0 && (c = vdev_mirror_child_select(zio)) != -1) {
787 		ASSERT(c >= 0 && c < mm->mm_children);
788 		mc = &mm->mm_child[c];
789 		zio_vdev_io_redone(zio);
790 		zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
791 		    mc->mc_vd, mc->mc_offset, zio->io_abd, zio->io_size,
792 		    ZIO_TYPE_READ, zio->io_priority, 0,
793 		    vdev_mirror_child_done, mc));
794 		return;
795 	}
796 
797 	/* XXPOLICY */
798 	if (good_copies == 0) {
799 		zio->io_error = vdev_mirror_worst_error(mm);
800 		ASSERT(zio->io_error != 0);
801 	}
802 
803 	if (good_copies && spa_writeable(zio->io_spa) &&
804 	    (unexpected_errors ||
805 	    (zio->io_flags & ZIO_FLAG_RESILVER) ||
806 	    ((zio->io_flags & ZIO_FLAG_SCRUB) && mm->mm_resilvering))) {
807 		/*
808 		 * Use the good data we have in hand to repair damaged children.
809 		 */
810 		for (c = 0; c < mm->mm_children; c++) {
811 			/*
812 			 * Don't rewrite known good children.
813 			 * Not only is it unnecessary, it could
814 			 * actually be harmful: if the system lost
815 			 * power while rewriting the only good copy,
816 			 * there would be no good copies left!
817 			 */
818 			mc = &mm->mm_child[c];
819 
820 			if (mc->mc_error == 0) {
821 				vdev_ops_t *ops = mc->mc_vd->vdev_ops;
822 
823 				if (mc->mc_tried)
824 					continue;
825 				/*
826 				 * We didn't try this child.  We need to
827 				 * repair it if:
828 				 * 1. it's a scrub (in which case we have
829 				 * tried everything that was healthy)
830 				 *  - or -
831 				 * 2. it's an indirect or distributed spare
832 				 * vdev (in which case it could point to any
833 				 * other vdev, which might have a bad DTL)
834 				 *  - or -
835 				 * 3. the DTL indicates that this data is
836 				 * missing from this vdev
837 				 */
838 				if (!(zio->io_flags & ZIO_FLAG_SCRUB) &&
839 				    ops != &vdev_indirect_ops &&
840 				    ops != &vdev_draid_spare_ops &&
841 				    !vdev_dtl_contains(mc->mc_vd, DTL_PARTIAL,
842 				    zio->io_txg, 1))
843 					continue;
844 				mc->mc_error = SET_ERROR(ESTALE);
845 			}
846 
847 			zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
848 			    mc->mc_vd, mc->mc_offset,
849 			    zio->io_abd, zio->io_size, ZIO_TYPE_WRITE,
850 			    zio->io_priority == ZIO_PRIORITY_REBUILD ?
851 			    ZIO_PRIORITY_REBUILD : ZIO_PRIORITY_ASYNC_WRITE,
852 			    ZIO_FLAG_IO_REPAIR | (unexpected_errors ?
853 			    ZIO_FLAG_SELF_HEAL : 0), NULL, NULL));
854 		}
855 	}
856 }
857 
858 static void
859 vdev_mirror_state_change(vdev_t *vd, int faulted, int degraded)
860 {
861 	if (faulted == vd->vdev_children) {
862 		if (vdev_children_are_offline(vd)) {
863 			vdev_set_state(vd, B_FALSE, VDEV_STATE_OFFLINE,
864 			    VDEV_AUX_CHILDREN_OFFLINE);
865 		} else {
866 			vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
867 			    VDEV_AUX_NO_REPLICAS);
868 		}
869 	} else if (degraded + faulted != 0) {
870 		vdev_set_state(vd, B_FALSE, VDEV_STATE_DEGRADED, VDEV_AUX_NONE);
871 	} else {
872 		vdev_set_state(vd, B_FALSE, VDEV_STATE_HEALTHY, VDEV_AUX_NONE);
873 	}
874 }
875 
876 /*
877  * Return the maximum asize for a rebuild zio in the provided range.
878  */
879 static uint64_t
880 vdev_mirror_rebuild_asize(vdev_t *vd, uint64_t start, uint64_t asize,
881     uint64_t max_segment)
882 {
883 	uint64_t psize = MIN(P2ROUNDUP(max_segment, 1 << vd->vdev_ashift),
884 	    SPA_MAXBLOCKSIZE);
885 
886 	return (MIN(asize, vdev_psize_to_asize(vd, psize)));
887 }
888 
889 vdev_ops_t vdev_mirror_ops = {
890 	.vdev_op_init = NULL,
891 	.vdev_op_fini = NULL,
892 	.vdev_op_open = vdev_mirror_open,
893 	.vdev_op_close = vdev_mirror_close,
894 	.vdev_op_asize = vdev_default_asize,
895 	.vdev_op_min_asize = vdev_default_min_asize,
896 	.vdev_op_min_alloc = NULL,
897 	.vdev_op_io_start = vdev_mirror_io_start,
898 	.vdev_op_io_done = vdev_mirror_io_done,
899 	.vdev_op_state_change = vdev_mirror_state_change,
900 	.vdev_op_need_resilver = vdev_default_need_resilver,
901 	.vdev_op_hold = NULL,
902 	.vdev_op_rele = NULL,
903 	.vdev_op_remap = NULL,
904 	.vdev_op_xlate = vdev_default_xlate,
905 	.vdev_op_rebuild_asize = vdev_mirror_rebuild_asize,
906 	.vdev_op_metaslab_init = NULL,
907 	.vdev_op_config_generate = NULL,
908 	.vdev_op_nparity = NULL,
909 	.vdev_op_ndisks = NULL,
910 	.vdev_op_type = VDEV_TYPE_MIRROR,	/* name of this vdev type */
911 	.vdev_op_leaf = B_FALSE			/* not a leaf vdev */
912 };
913 
914 vdev_ops_t vdev_replacing_ops = {
915 	.vdev_op_init = NULL,
916 	.vdev_op_fini = NULL,
917 	.vdev_op_open = vdev_mirror_open,
918 	.vdev_op_close = vdev_mirror_close,
919 	.vdev_op_asize = vdev_default_asize,
920 	.vdev_op_min_asize = vdev_default_min_asize,
921 	.vdev_op_min_alloc = NULL,
922 	.vdev_op_io_start = vdev_mirror_io_start,
923 	.vdev_op_io_done = vdev_mirror_io_done,
924 	.vdev_op_state_change = vdev_mirror_state_change,
925 	.vdev_op_need_resilver = vdev_default_need_resilver,
926 	.vdev_op_hold = NULL,
927 	.vdev_op_rele = NULL,
928 	.vdev_op_remap = NULL,
929 	.vdev_op_xlate = vdev_default_xlate,
930 	.vdev_op_rebuild_asize = vdev_mirror_rebuild_asize,
931 	.vdev_op_metaslab_init = NULL,
932 	.vdev_op_config_generate = NULL,
933 	.vdev_op_nparity = NULL,
934 	.vdev_op_ndisks = NULL,
935 	.vdev_op_type = VDEV_TYPE_REPLACING,	/* name of this vdev type */
936 	.vdev_op_leaf = B_FALSE			/* not a leaf vdev */
937 };
938 
939 vdev_ops_t vdev_spare_ops = {
940 	.vdev_op_init = NULL,
941 	.vdev_op_fini = NULL,
942 	.vdev_op_open = vdev_mirror_open,
943 	.vdev_op_close = vdev_mirror_close,
944 	.vdev_op_asize = vdev_default_asize,
945 	.vdev_op_min_asize = vdev_default_min_asize,
946 	.vdev_op_min_alloc = NULL,
947 	.vdev_op_io_start = vdev_mirror_io_start,
948 	.vdev_op_io_done = vdev_mirror_io_done,
949 	.vdev_op_state_change = vdev_mirror_state_change,
950 	.vdev_op_need_resilver = vdev_default_need_resilver,
951 	.vdev_op_hold = NULL,
952 	.vdev_op_rele = NULL,
953 	.vdev_op_remap = NULL,
954 	.vdev_op_xlate = vdev_default_xlate,
955 	.vdev_op_rebuild_asize = vdev_mirror_rebuild_asize,
956 	.vdev_op_metaslab_init = NULL,
957 	.vdev_op_config_generate = NULL,
958 	.vdev_op_nparity = NULL,
959 	.vdev_op_ndisks = NULL,
960 	.vdev_op_type = VDEV_TYPE_SPARE,	/* name of this vdev type */
961 	.vdev_op_leaf = B_FALSE			/* not a leaf vdev */
962 };
963 
964 /* BEGIN CSTYLED */
965 ZFS_MODULE_PARAM(zfs_vdev_mirror, zfs_vdev_mirror_, rotating_inc, INT, ZMOD_RW,
966 	"Rotating media load increment for non-seeking I/O's");
967 
968 ZFS_MODULE_PARAM(zfs_vdev_mirror, zfs_vdev_mirror_, rotating_seek_inc, INT, ZMOD_RW,
969 	"Rotating media load increment for seeking I/O's");
970 
971 ZFS_MODULE_PARAM(zfs_vdev_mirror, zfs_vdev_mirror_, rotating_seek_offset, INT, ZMOD_RW,
972 	"Offset in bytes from the last I/O which triggers "
973 	"a reduced rotating media seek increment");
974 
975 ZFS_MODULE_PARAM(zfs_vdev_mirror, zfs_vdev_mirror_, non_rotating_inc, INT, ZMOD_RW,
976 	"Non-rotating media load increment for non-seeking I/O's");
977 
978 ZFS_MODULE_PARAM(zfs_vdev_mirror, zfs_vdev_mirror_, non_rotating_seek_inc, INT, ZMOD_RW,
979 	"Non-rotating media load increment for seeking I/O's");
980 /* END CSTYLED */
981