Move the world out of /zfs/ and seperate out module build tree

1 files changed, 1209 insertions, 0 deletions

diff --git a/module/zfs/vdev_raidz.c b/module/zfs/vdev_raidz.c
new file mode 100644
index 000000000..69e314468
--- /dev/null
+++ b/module/zfs/vdev_raidz.c
@@ -0,0 +1,1209 @@
+/*
+ * 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 2008 Sun Microsystems, Inc.  All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#include <sys/zfs_context.h>
+#include <sys/spa.h>
+#include <sys/vdev_impl.h>
+#include <sys/zio.h>
+#include <sys/zio_checksum.h>
+#include <sys/fs/zfs.h>
+#include <sys/fm/fs/zfs.h>
+
+/*
+ * Virtual device vector for RAID-Z.
+ *
+ * This vdev supports both single and double parity. For single parity, we
+ * use a simple XOR of all the data columns. For double parity, we use both
+ * the simple XOR as well as a technique described in "The mathematics of
+ * RAID-6" by H. Peter Anvin. This technique defines a Galois field, GF(2^8),
+ * over the integers expressable in a single byte. Briefly, the operations on
+ * the field are defined as follows:
+ *
+ *   o addition (+) is represented by a bitwise XOR
+ *   o subtraction (-) is therefore identical to addition: A + B = A - B
+ *   o multiplication of A by 2 is defined by the following bitwise expression:
+ *	(A * 2)_7 = A_6
+ *	(A * 2)_6 = A_5
+ *	(A * 2)_5 = A_4
+ *	(A * 2)_4 = A_3 + A_7
+ *	(A * 2)_3 = A_2 + A_7
+ *	(A * 2)_2 = A_1 + A_7
+ *	(A * 2)_1 = A_0
+ *	(A * 2)_0 = A_7
+ *
+ * In C, multiplying by 2 is therefore ((a << 1) ^ ((a & 0x80) ? 0x1d : 0)).
+ *
+ * Observe that any number in the field (except for 0) can be expressed as a
+ * power of 2 -- a generator for the field. We store a table of the powers of
+ * 2 and logs base 2 for quick look ups, and exploit the fact that A * B can
+ * be rewritten as 2^(log_2(A) + log_2(B)) (where '+' is normal addition rather
+ * than field addition). The inverse of a field element A (A^-1) is A^254.
+ *
+ * The two parity columns, P and Q, over several data columns, D_0, ... D_n-1,
+ * can be expressed by field operations:
+ *
+ *	P = D_0 + D_1 + ... + D_n-2 + D_n-1
+ *	Q = 2^n-1 * D_0 + 2^n-2 * D_1 + ... + 2^1 * D_n-2 + 2^0 * D_n-1
+ *	  = ((...((D_0) * 2 + D_1) * 2 + ...) * 2 + D_n-2) * 2 + D_n-1
+ *
+ * See the reconstruction code below for how P and Q can used individually or
+ * in concert to recover missing data columns.
+ */
+
+typedef struct raidz_col {
+	uint64_t rc_devidx;		/* child device index for I/O */
+	uint64_t rc_offset;		/* device offset */
+	uint64_t rc_size;		/* I/O size */
+	void *rc_data;			/* I/O data */
+	int rc_error;			/* I/O error for this device */
+	uint8_t rc_tried;		/* Did we attempt this I/O column? */
+	uint8_t rc_skipped;		/* Did we skip this I/O column? */
+} raidz_col_t;
+
+typedef struct raidz_map {
+	uint64_t rm_cols;		/* Column count */
+	uint64_t rm_bigcols;		/* Number of oversized columns */
+	uint64_t rm_asize;		/* Actual total I/O size */
+	uint64_t rm_missingdata;	/* Count of missing data devices */
+	uint64_t rm_missingparity;	/* Count of missing parity devices */
+	uint64_t rm_firstdatacol;	/* First data column/parity count */
+	raidz_col_t rm_col[1];		/* Flexible array of I/O columns */
+} raidz_map_t;
+
+#define	VDEV_RAIDZ_P		0
+#define	VDEV_RAIDZ_Q		1
+
+#define	VDEV_RAIDZ_MAXPARITY	2
+
+#define	VDEV_RAIDZ_MUL_2(a)	(((a) << 1) ^ (((a) & 0x80) ? 0x1d : 0))
+
+/*
+ * These two tables represent powers and logs of 2 in the Galois field defined
+ * above. These values were computed by repeatedly multiplying by 2 as above.
+ */
+static const uint8_t vdev_raidz_pow2[256] = {
+	0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80,
+	0x1d, 0x3a, 0x74, 0xe8, 0xcd, 0x87, 0x13, 0x26,
+	0x4c, 0x98, 0x2d, 0x5a, 0xb4, 0x75, 0xea, 0xc9,
+	0x8f, 0x03, 0x06, 0x0c, 0x18, 0x30, 0x60, 0xc0,
+	0x9d, 0x27, 0x4e, 0x9c, 0x25, 0x4a, 0x94, 0x35,
+	0x6a, 0xd4, 0xb5, 0x77, 0xee, 0xc1, 0x9f, 0x23,
+	0x46, 0x8c, 0x05, 0x0a, 0x14, 0x28, 0x50, 0xa0,
+	0x5d, 0xba, 0x69, 0xd2, 0xb9, 0x6f, 0xde, 0xa1,
+	0x5f, 0xbe, 0x61, 0xc2, 0x99, 0x2f, 0x5e, 0xbc,
+	0x65, 0xca, 0x89, 0x0f, 0x1e, 0x3c, 0x78, 0xf0,
+	0xfd, 0xe7, 0xd3, 0xbb, 0x6b, 0xd6, 0xb1, 0x7f,
+	0xfe, 0xe1, 0xdf, 0xa3, 0x5b, 0xb6, 0x71, 0xe2,
+	0xd9, 0xaf, 0x43, 0x86, 0x11, 0x22, 0x44, 0x88,
+	0x0d, 0x1a, 0x34, 0x68, 0xd0, 0xbd, 0x67, 0xce,
+	0x81, 0x1f, 0x3e, 0x7c, 0xf8, 0xed, 0xc7, 0x93,
+	0x3b, 0x76, 0xec, 0xc5, 0x97, 0x33, 0x66, 0xcc,
+	0x85, 0x17, 0x2e, 0x5c, 0xb8, 0x6d, 0xda, 0xa9,
+	0x4f, 0x9e, 0x21, 0x42, 0x84, 0x15, 0x2a, 0x54,
+	0xa8, 0x4d, 0x9a, 0x29, 0x52, 0xa4, 0x55, 0xaa,
+	0x49, 0x92, 0x39, 0x72, 0xe4, 0xd5, 0xb7, 0x73,
+	0xe6, 0xd1, 0xbf, 0x63, 0xc6, 0x91, 0x3f, 0x7e,
+	0xfc, 0xe5, 0xd7, 0xb3, 0x7b, 0xf6, 0xf1, 0xff,
+	0xe3, 0xdb, 0xab, 0x4b, 0x96, 0x31, 0x62, 0xc4,
+	0x95, 0x37, 0x6e, 0xdc, 0xa5, 0x57, 0xae, 0x41,
+	0x82, 0x19, 0x32, 0x64, 0xc8, 0x8d, 0x07, 0x0e,
+	0x1c, 0x38, 0x70, 0xe0, 0xdd, 0xa7, 0x53, 0xa6,
+	0x51, 0xa2, 0x59, 0xb2, 0x79, 0xf2, 0xf9, 0xef,
+	0xc3, 0x9b, 0x2b, 0x56, 0xac, 0x45, 0x8a, 0x09,
+	0x12, 0x24, 0x48, 0x90, 0x3d, 0x7a, 0xf4, 0xf5,
+	0xf7, 0xf3, 0xfb, 0xeb, 0xcb, 0x8b, 0x0b, 0x16,
+	0x2c, 0x58, 0xb0, 0x7d, 0xfa, 0xe9, 0xcf, 0x83,
+	0x1b, 0x36, 0x6c, 0xd8, 0xad, 0x47, 0x8e, 0x01
+};
+static const uint8_t vdev_raidz_log2[256] = {
+	0x00, 0x00, 0x01, 0x19, 0x02, 0x32, 0x1a, 0xc6,
+	0x03, 0xdf, 0x33, 0xee, 0x1b, 0x68, 0xc7, 0x4b,
+	0x04, 0x64, 0xe0, 0x0e, 0x34, 0x8d, 0xef, 0x81,
+	0x1c, 0xc1, 0x69, 0xf8, 0xc8, 0x08, 0x4c, 0x71,
+	0x05, 0x8a, 0x65, 0x2f, 0xe1, 0x24, 0x0f, 0x21,
+	0x35, 0x93, 0x8e, 0xda, 0xf0, 0x12, 0x82, 0x45,
+	0x1d, 0xb5, 0xc2, 0x7d, 0x6a, 0x27, 0xf9, 0xb9,
+	0xc9, 0x9a, 0x09, 0x78, 0x4d, 0xe4, 0x72, 0xa6,
+	0x06, 0xbf, 0x8b, 0x62, 0x66, 0xdd, 0x30, 0xfd,
+	0xe2, 0x98, 0x25, 0xb3, 0x10, 0x91, 0x22, 0x88,
+	0x36, 0xd0, 0x94, 0xce, 0x8f, 0x96, 0xdb, 0xbd,
+	0xf1, 0xd2, 0x13, 0x5c, 0x83, 0x38, 0x46, 0x40,
+	0x1e, 0x42, 0xb6, 0xa3, 0xc3, 0x48, 0x7e, 0x6e,
+	0x6b, 0x3a, 0x28, 0x54, 0xfa, 0x85, 0xba, 0x3d,
+	0xca, 0x5e, 0x9b, 0x9f, 0x0a, 0x15, 0x79, 0x2b,
+	0x4e, 0xd4, 0xe5, 0xac, 0x73, 0xf3, 0xa7, 0x57,
+	0x07, 0x70, 0xc0, 0xf7, 0x8c, 0x80, 0x63, 0x0d,
+	0x67, 0x4a, 0xde, 0xed, 0x31, 0xc5, 0xfe, 0x18,
+	0xe3, 0xa5, 0x99, 0x77, 0x26, 0xb8, 0xb4, 0x7c,
+	0x11, 0x44, 0x92, 0xd9, 0x23, 0x20, 0x89, 0x2e,
+	0x37, 0x3f, 0xd1, 0x5b, 0x95, 0xbc, 0xcf, 0xcd,
+	0x90, 0x87, 0x97, 0xb2, 0xdc, 0xfc, 0xbe, 0x61,
+	0xf2, 0x56, 0xd3, 0xab, 0x14, 0x2a, 0x5d, 0x9e,
+	0x84, 0x3c, 0x39, 0x53, 0x47, 0x6d, 0x41, 0xa2,
+	0x1f, 0x2d, 0x43, 0xd8, 0xb7, 0x7b, 0xa4, 0x76,
+	0xc4, 0x17, 0x49, 0xec, 0x7f, 0x0c, 0x6f, 0xf6,
+	0x6c, 0xa1, 0x3b, 0x52, 0x29, 0x9d, 0x55, 0xaa,
+	0xfb, 0x60, 0x86, 0xb1, 0xbb, 0xcc, 0x3e, 0x5a,
+	0xcb, 0x59, 0x5f, 0xb0, 0x9c, 0xa9, 0xa0, 0x51,
+	0x0b, 0xf5, 0x16, 0xeb, 0x7a, 0x75, 0x2c, 0xd7,
+	0x4f, 0xae, 0xd5, 0xe9, 0xe6, 0xe7, 0xad, 0xe8,
+	0x74, 0xd6, 0xf4, 0xea, 0xa8, 0x50, 0x58, 0xaf,
+};
+
+/*
+ * Multiply a given number by 2 raised to the given power.
+ */
+static uint8_t
+vdev_raidz_exp2(uint_t a, int exp)
+{
+	if (a == 0)
+		return (0);
+
+	ASSERT(exp >= 0);
+	ASSERT(vdev_raidz_log2[a] > 0 || a == 1);
+
+	exp += vdev_raidz_log2[a];
+	if (exp > 255)
+		exp -= 255;
+
+	return (vdev_raidz_pow2[exp]);
+}
+
+static void
+vdev_raidz_map_free(zio_t *zio)
+{
+	raidz_map_t *rm = zio->io_vsd;
+	int c;
+
+	for (c = 0; c < rm->rm_firstdatacol; c++)
+		zio_buf_free(rm->rm_col[c].rc_data, rm->rm_col[c].rc_size);
+
+	kmem_free(rm, offsetof(raidz_map_t, rm_col[rm->rm_cols]));
+}
+
+static raidz_map_t *
+vdev_raidz_map_alloc(zio_t *zio, uint64_t unit_shift, uint64_t dcols,
+    uint64_t nparity)
+{
+	raidz_map_t *rm;
+	uint64_t b = zio->io_offset >> unit_shift;
+	uint64_t s = zio->io_size >> unit_shift;
+	uint64_t f = b % dcols;
+	uint64_t o = (b / dcols) << unit_shift;
+	uint64_t q, r, c, bc, col, acols, coff, devidx;
+
+	q = s / (dcols - nparity);
+	r = s - q * (dcols - nparity);
+	bc = (r == 0 ? 0 : r + nparity);
+
+	acols = (q == 0 ? bc : dcols);
+
+	rm = kmem_alloc(offsetof(raidz_map_t, rm_col[acols]), KM_SLEEP);
+
+	rm->rm_cols = acols;
+	rm->rm_bigcols = bc;
+	rm->rm_asize = 0;
+	rm->rm_missingdata = 0;
+	rm->rm_missingparity = 0;
+	rm->rm_firstdatacol = nparity;
+
+	for (c = 0; c < acols; c++) {
+		col = f + c;
+		coff = o;
+		if (col >= dcols) {
+			col -= dcols;
+			coff += 1ULL << unit_shift;
+		}
+		rm->rm_col[c].rc_devidx = col;
+		rm->rm_col[c].rc_offset = coff;
+		rm->rm_col[c].rc_size = (q + (c < bc)) << unit_shift;
+		rm->rm_col[c].rc_data = NULL;
+		rm->rm_col[c].rc_error = 0;
+		rm->rm_col[c].rc_tried = 0;
+		rm->rm_col[c].rc_skipped = 0;
+		rm->rm_asize += rm->rm_col[c].rc_size;
+	}
+
+	rm->rm_asize = roundup(rm->rm_asize, (nparity + 1) << unit_shift);
+
+	for (c = 0; c < rm->rm_firstdatacol; c++)
+		rm->rm_col[c].rc_data = zio_buf_alloc(rm->rm_col[c].rc_size);
+
+	rm->rm_col[c].rc_data = zio->io_data;
+
+	for (c = c + 1; c < acols; c++)
+		rm->rm_col[c].rc_data = (char *)rm->rm_col[c - 1].rc_data +
+		    rm->rm_col[c - 1].rc_size;
+
+	/*
+	 * If all data stored spans all columns, there's a danger that parity
+	 * will always be on the same device and, since parity isn't read
+	 * during normal operation, that that device's I/O bandwidth won't be
+	 * used effectively. We therefore switch the parity every 1MB.
+	 *
+	 * ... at least that was, ostensibly, the theory. As a practical
+	 * matter unless we juggle the parity between all devices evenly, we
+	 * won't see any benefit. Further, occasional writes that aren't a
+	 * multiple of the LCM of the number of children and the minimum
+	 * stripe width are sufficient to avoid pessimal behavior.
+	 * Unfortunately, this decision created an implicit on-disk format
+	 * requirement that we need to support for all eternity, but only
+	 * for single-parity RAID-Z.
+	 */
+	ASSERT(rm->rm_cols >= 2);
+	ASSERT(rm->rm_col[0].rc_size == rm->rm_col[1].rc_size);
+
+	if (rm->rm_firstdatacol == 1 && (zio->io_offset & (1ULL << 20))) {
+		devidx = rm->rm_col[0].rc_devidx;
+		o = rm->rm_col[0].rc_offset;
+		rm->rm_col[0].rc_devidx = rm->rm_col[1].rc_devidx;
+		rm->rm_col[0].rc_offset = rm->rm_col[1].rc_offset;
+		rm->rm_col[1].rc_devidx = devidx;
+		rm->rm_col[1].rc_offset = o;
+	}
+
+	zio->io_vsd = rm;
+	zio->io_vsd_free = vdev_raidz_map_free;
+	return (rm);
+}
+
+static void
+vdev_raidz_generate_parity_p(raidz_map_t *rm)
+{
+	uint64_t *p, *src, pcount, ccount, i;
+	int c;
+
+	pcount = rm->rm_col[VDEV_RAIDZ_P].rc_size / sizeof (src[0]);
+
+	for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+		src = rm->rm_col[c].rc_data;
+		p = rm->rm_col[VDEV_RAIDZ_P].rc_data;
+		ccount = rm->rm_col[c].rc_size / sizeof (src[0]);
+
+		if (c == rm->rm_firstdatacol) {
+			ASSERT(ccount == pcount);
+			for (i = 0; i < ccount; i++, p++, src++) {
+				*p = *src;
+			}
+		} else {
+			ASSERT(ccount <= pcount);
+			for (i = 0; i < ccount; i++, p++, src++) {
+				*p ^= *src;
+			}
+		}
+	}
+}
+
+static void
+vdev_raidz_generate_parity_pq(raidz_map_t *rm)
+{
+	uint64_t *q, *p, *src, pcount, ccount, mask, i;
+	int c;
+
+	pcount = rm->rm_col[VDEV_RAIDZ_P].rc_size / sizeof (src[0]);
+	ASSERT(rm->rm_col[VDEV_RAIDZ_P].rc_size ==
+	    rm->rm_col[VDEV_RAIDZ_Q].rc_size);
+
+	for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+		src = rm->rm_col[c].rc_data;
+		p = rm->rm_col[VDEV_RAIDZ_P].rc_data;
+		q = rm->rm_col[VDEV_RAIDZ_Q].rc_data;
+		ccount = rm->rm_col[c].rc_size / sizeof (src[0]);
+
+		if (c == rm->rm_firstdatacol) {
+			ASSERT(ccount == pcount || ccount == 0);
+			for (i = 0; i < ccount; i++, p++, q++, src++) {
+				*q = *src;
+				*p = *src;
+			}
+			for (; i < pcount; i++, p++, q++, src++) {
+				*q = 0;
+				*p = 0;
+			}
+		} else {
+			ASSERT(ccount <= pcount);
+
+			/*
+			 * Rather than multiplying each byte individually (as
+			 * described above), we are able to handle 8 at once
+			 * by generating a mask based on the high bit in each
+			 * byte and using that to conditionally XOR in 0x1d.
+			 */
+			for (i = 0; i < ccount; i++, p++, q++, src++) {
+				mask = *q & 0x8080808080808080ULL;
+				mask = (mask << 1) - (mask >> 7);
+				*q = ((*q << 1) & 0xfefefefefefefefeULL) ^
+				    (mask & 0x1d1d1d1d1d1d1d1dULL);
+				*q ^= *src;
+				*p ^= *src;
+			}
+
+			/*
+			 * Treat short columns as though they are full of 0s.
+			 */
+			for (; i < pcount; i++, q++) {
+				mask = *q & 0x8080808080808080ULL;
+				mask = (mask << 1) - (mask >> 7);
+				*q = ((*q << 1) & 0xfefefefefefefefeULL) ^
+				    (mask & 0x1d1d1d1d1d1d1d1dULL);
+			}
+		}
+	}
+}
+
+static void
+vdev_raidz_reconstruct_p(raidz_map_t *rm, int x)
+{
+	uint64_t *dst, *src, xcount, ccount, count, i;
+	int c;
+
+	xcount = rm->rm_col[x].rc_size / sizeof (src[0]);
+	ASSERT(xcount <= rm->rm_col[VDEV_RAIDZ_P].rc_size / sizeof (src[0]));
+	ASSERT(xcount > 0);
+
+	src = rm->rm_col[VDEV_RAIDZ_P].rc_data;
+	dst = rm->rm_col[x].rc_data;
+	for (i = 0; i < xcount; i++, dst++, src++) {
+		*dst = *src;
+	}
+
+	for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+		src = rm->rm_col[c].rc_data;
+		dst = rm->rm_col[x].rc_data;
+
+		if (c == x)
+			continue;
+
+		ccount = rm->rm_col[c].rc_size / sizeof (src[0]);
+		count = MIN(ccount, xcount);
+
+		for (i = 0; i < count; i++, dst++, src++) {
+			*dst ^= *src;
+		}
+	}
+}
+
+static void
+vdev_raidz_reconstruct_q(raidz_map_t *rm, int x)
+{
+	uint64_t *dst, *src, xcount, ccount, count, mask, i;
+	uint8_t *b;
+	int c, j, exp;
+
+	xcount = rm->rm_col[x].rc_size / sizeof (src[0]);
+	ASSERT(xcount <= rm->rm_col[VDEV_RAIDZ_Q].rc_size / sizeof (src[0]));
+
+	for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+		src = rm->rm_col[c].rc_data;
+		dst = rm->rm_col[x].rc_data;
+
+		if (c == x)
+			ccount = 0;
+		else
+			ccount = rm->rm_col[c].rc_size / sizeof (src[0]);
+
+		count = MIN(ccount, xcount);
+
+		if (c == rm->rm_firstdatacol) {
+			for (i = 0; i < count; i++, dst++, src++) {
+				*dst = *src;
+			}
+			for (; i < xcount; i++, dst++) {
+				*dst = 0;
+			}
+
+		} else {
+			/*
+			 * For an explanation of this, see the comment in
+			 * vdev_raidz_generate_parity_pq() above.
+			 */
+			for (i = 0; i < count; i++, dst++, src++) {
+				mask = *dst & 0x8080808080808080ULL;
+				mask = (mask << 1) - (mask >> 7);
+				*dst = ((*dst << 1) & 0xfefefefefefefefeULL) ^
+				    (mask & 0x1d1d1d1d1d1d1d1dULL);
+				*dst ^= *src;
+			}
+
+			for (; i < xcount; i++, dst++) {
+				mask = *dst & 0x8080808080808080ULL;
+				mask = (mask << 1) - (mask >> 7);
+				*dst = ((*dst << 1) & 0xfefefefefefefefeULL) ^
+				    (mask & 0x1d1d1d1d1d1d1d1dULL);
+			}
+		}
+	}
+
+	src = rm->rm_col[VDEV_RAIDZ_Q].rc_data;
+	dst = rm->rm_col[x].rc_data;
+	exp = 255 - (rm->rm_cols - 1 - x);
+
+	for (i = 0; i < xcount; i++, dst++, src++) {
+		*dst ^= *src;
+		for (j = 0, b = (uint8_t *)dst; j < 8; j++, b++) {
+			*b = vdev_raidz_exp2(*b, exp);
+		}
+	}
+}
+
+static void
+vdev_raidz_reconstruct_pq(raidz_map_t *rm, int x, int y)
+{
+	uint8_t *p, *q, *pxy, *qxy, *xd, *yd, tmp, a, b, aexp, bexp;
+	void *pdata, *qdata;
+	uint64_t xsize, ysize, i;
+
+	ASSERT(x < y);
+	ASSERT(x >= rm->rm_firstdatacol);
+	ASSERT(y < rm->rm_cols);
+
+	ASSERT(rm->rm_col[x].rc_size >= rm->rm_col[y].rc_size);
+
+	/*
+	 * Move the parity data aside -- we're going to compute parity as
+	 * though columns x and y were full of zeros -- Pxy and Qxy. We want to
+	 * reuse the parity generation mechanism without trashing the actual
+	 * parity so we make those columns appear to be full of zeros by
+	 * setting their lengths to zero.
+	 */
+	pdata = rm->rm_col[VDEV_RAIDZ_P].rc_data;
+	qdata = rm->rm_col[VDEV_RAIDZ_Q].rc_data;
+	xsize = rm->rm_col[x].rc_size;
+	ysize = rm->rm_col[y].rc_size;
+
+	rm->rm_col[VDEV_RAIDZ_P].rc_data =
+	    zio_buf_alloc(rm->rm_col[VDEV_RAIDZ_P].rc_size);
+	rm->rm_col[VDEV_RAIDZ_Q].rc_data =
+	    zio_buf_alloc(rm->rm_col[VDEV_RAIDZ_Q].rc_size);
+	rm->rm_col[x].rc_size = 0;
+	rm->rm_col[y].rc_size = 0;
+
+	vdev_raidz_generate_parity_pq(rm);
+
+	rm->rm_col[x].rc_size = xsize;
+	rm->rm_col[y].rc_size = ysize;
+
+	p = pdata;
+	q = qdata;
+	pxy = rm->rm_col[VDEV_RAIDZ_P].rc_data;
+	qxy = rm->rm_col[VDEV_RAIDZ_Q].rc_data;
+	xd = rm->rm_col[x].rc_data;
+	yd = rm->rm_col[y].rc_data;
+
+	/*
+	 * We now have:
+	 *	Pxy = P + D_x + D_y
+	 *	Qxy = Q + 2^(ndevs - 1 - x) * D_x + 2^(ndevs - 1 - y) * D_y
+	 *
+	 * We can then solve for D_x:
+	 *	D_x = A * (P + Pxy) + B * (Q + Qxy)
+	 * where
+	 *	A = 2^(x - y) * (2^(x - y) + 1)^-1
+	 *	B = 2^(ndevs - 1 - x) * (2^(x - y) + 1)^-1
+	 *
+	 * With D_x in hand, we can easily solve for D_y:
+	 *	D_y = P + Pxy + D_x
+	 */
+
+	a = vdev_raidz_pow2[255 + x - y];
+	b = vdev_raidz_pow2[255 - (rm->rm_cols - 1 - x)];
+	tmp = 255 - vdev_raidz_log2[a ^ 1];
+
+	aexp = vdev_raidz_log2[vdev_raidz_exp2(a, tmp)];
+	bexp = vdev_raidz_log2[vdev_raidz_exp2(b, tmp)];
+
+	for (i = 0; i < xsize; i++, p++, q++, pxy++, qxy++, xd++, yd++) {
+		*xd = vdev_raidz_exp2(*p ^ *pxy, aexp) ^
+		    vdev_raidz_exp2(*q ^ *qxy, bexp);
+
+		if (i < ysize)
+			*yd = *p ^ *pxy ^ *xd;
+	}
+
+	zio_buf_free(rm->rm_col[VDEV_RAIDZ_P].rc_data,
+	    rm->rm_col[VDEV_RAIDZ_P].rc_size);
+	zio_buf_free(rm->rm_col[VDEV_RAIDZ_Q].rc_data,
+	    rm->rm_col[VDEV_RAIDZ_Q].rc_size);
+
+	/*
+	 * Restore the saved parity data.
+	 */
+	rm->rm_col[VDEV_RAIDZ_P].rc_data = pdata;
+	rm->rm_col[VDEV_RAIDZ_Q].rc_data = qdata;
+}
+
+
+static int
+vdev_raidz_open(vdev_t *vd, uint64_t *asize, uint64_t *ashift)
+{
+	vdev_t *cvd;
+	uint64_t nparity = vd->vdev_nparity;
+	int c, error;
+	int lasterror = 0;
+	int numerrors = 0;
+
+	ASSERT(nparity > 0);
+
+	if (nparity > VDEV_RAIDZ_MAXPARITY ||
+	    vd->vdev_children < nparity + 1) {
+		vd->vdev_stat.vs_aux = VDEV_AUX_BAD_LABEL;
+		return (EINVAL);
+	}
+
+	for (c = 0; c < vd->vdev_children; c++) {
+		cvd = vd->vdev_child[c];
+
+		if ((error = vdev_open(cvd)) != 0) {
+			lasterror = error;
+			numerrors++;
+			continue;
+		}
+
+		*asize = MIN(*asize - 1, cvd->vdev_asize - 1) + 1;
+		*ashift = MAX(*ashift, cvd->vdev_ashift);
+	}
+
+	*asize *= vd->vdev_children;
+
+	if (numerrors > nparity) {
+		vd->vdev_stat.vs_aux = VDEV_AUX_NO_REPLICAS;
+		return (lasterror);
+	}
+
+	return (0);
+}
+
+static void
+vdev_raidz_close(vdev_t *vd)
+{
+	int c;
+
+	for (c = 0; c < vd->vdev_children; c++)
+		vdev_close(vd->vdev_child[c]);
+}
+
+static uint64_t
+vdev_raidz_asize(vdev_t *vd, uint64_t psize)
+{
+	uint64_t asize;
+	uint64_t ashift = vd->vdev_top->vdev_ashift;
+	uint64_t cols = vd->vdev_children;
+	uint64_t nparity = vd->vdev_nparity;
+
+	asize = ((psize - 1) >> ashift) + 1;
+	asize += nparity * ((asize + cols - nparity - 1) / (cols - nparity));
+	asize = roundup(asize, nparity + 1) << ashift;
+
+	return (asize);
+}
+
+static void
+vdev_raidz_child_done(zio_t *zio)
+{
+	raidz_col_t *rc = zio->io_private;
+
+	rc->rc_error = zio->io_error;
+	rc->rc_tried = 1;
+	rc->rc_skipped = 0;
+}
+
+static int
+vdev_raidz_io_start(zio_t *zio)
+{
+	vdev_t *vd = zio->io_vd;
+	vdev_t *tvd = vd->vdev_top;
+	vdev_t *cvd;
+	blkptr_t *bp = zio->io_bp;
+	raidz_map_t *rm;
+	raidz_col_t *rc;
+	int c;
+
+	rm = vdev_raidz_map_alloc(zio, tvd->vdev_ashift, vd->vdev_children,
+	    vd->vdev_nparity);
+
+	ASSERT3U(rm->rm_asize, ==, vdev_psize_to_asize(vd, zio->io_size));
+
+	if (zio->io_type == ZIO_TYPE_WRITE) {
+		/*
+		 * Generate RAID parity in the first virtual columns.
+		 */
+		if (rm->rm_firstdatacol == 1)
+			vdev_raidz_generate_parity_p(rm);
+		else
+			vdev_raidz_generate_parity_pq(rm);
+
+		for (c = 0; c < rm->rm_cols; c++) {
+			rc = &rm->rm_col[c];
+			cvd = vd->vdev_child[rc->rc_devidx];
+			zio_nowait(zio_vdev_child_io(zio, NULL, cvd,
+			    rc->rc_offset, rc->rc_data, rc->rc_size,
+			    zio->io_type, zio->io_priority, 0,
+			    vdev_raidz_child_done, rc));
+		}
+
+		return (ZIO_PIPELINE_CONTINUE);
+	}
+
+	ASSERT(zio->io_type == ZIO_TYPE_READ);
+
+	/*
+	 * Iterate over the columns in reverse order so that we hit the parity
+	 * last -- any errors along the way will force us to read the parity
+	 * data.
+	 */
+	for (c = rm->rm_cols - 1; c >= 0; c--) {
+		rc = &rm->rm_col[c];
+		cvd = vd->vdev_child[rc->rc_devidx];
+		if (!vdev_readable(cvd)) {
+			if (c >= rm->rm_firstdatacol)
+				rm->rm_missingdata++;
+			else
+				rm->rm_missingparity++;
+			rc->rc_error = ENXIO;
+			rc->rc_tried = 1;	/* don't even try */
+			rc->rc_skipped = 1;
+			continue;
+		}
+		if (vdev_dtl_contains(&cvd->vdev_dtl_map, bp->blk_birth, 1)) {
+			if (c >= rm->rm_firstdatacol)
+				rm->rm_missingdata++;
+			else
+				rm->rm_missingparity++;
+			rc->rc_error = ESTALE;
+			rc->rc_skipped = 1;
+			continue;
+		}
+		if (c >= rm->rm_firstdatacol || rm->rm_missingdata > 0 ||
+		    (zio->io_flags & ZIO_FLAG_SCRUB)) {
+			zio_nowait(zio_vdev_child_io(zio, NULL, cvd,
+			    rc->rc_offset, rc->rc_data, rc->rc_size,
+			    zio->io_type, zio->io_priority, 0,
+			    vdev_raidz_child_done, rc));
+		}
+	}
+
+	return (ZIO_PIPELINE_CONTINUE);
+}
+
+/*
+ * Report a checksum error for a child of a RAID-Z device.
+ */
+static void
+raidz_checksum_error(zio_t *zio, raidz_col_t *rc)
+{
+	vdev_t *vd = zio->io_vd->vdev_child[rc->rc_devidx];
+
+	if (!(zio->io_flags & ZIO_FLAG_SPECULATIVE)) {
+		mutex_enter(&vd->vdev_stat_lock);
+		vd->vdev_stat.vs_checksum_errors++;
+		mutex_exit(&vd->vdev_stat_lock);
+	}
+
+	if (!(zio->io_flags & ZIO_FLAG_SPECULATIVE))
+		zfs_ereport_post(FM_EREPORT_ZFS_CHECKSUM,
+		    zio->io_spa, vd, zio, rc->rc_offset, rc->rc_size);
+}
+
+/*
+ * Generate the parity from the data columns. If we tried and were able to
+ * read the parity without error, verify that the generated parity matches the
+ * data we read. If it doesn't, we fire off a checksum error. Return the
+ * number such failures.
+ */
+static int
+raidz_parity_verify(zio_t *zio, raidz_map_t *rm)
+{
+	void *orig[VDEV_RAIDZ_MAXPARITY];
+	int c, ret = 0;
+	raidz_col_t *rc;
+
+	for (c = 0; c < rm->rm_firstdatacol; c++) {
+		rc = &rm->rm_col[c];
+		if (!rc->rc_tried || rc->rc_error != 0)
+			continue;
+		orig[c] = zio_buf_alloc(rc->rc_size);
+		bcopy(rc->rc_data, orig[c], rc->rc_size);
+	}
+
+	if (rm->rm_firstdatacol == 1)
+		vdev_raidz_generate_parity_p(rm);
+	else
+		vdev_raidz_generate_parity_pq(rm);
+
+	for (c = 0; c < rm->rm_firstdatacol; c++) {
+		rc = &rm->rm_col[c];
+		if (!rc->rc_tried || rc->rc_error != 0)
+			continue;
+		if (bcmp(orig[c], rc->rc_data, rc->rc_size) != 0) {
+			raidz_checksum_error(zio, rc);
+			rc->rc_error = ECKSUM;
+			ret++;
+		}
+		zio_buf_free(orig[c], rc->rc_size);
+	}
+
+	return (ret);
+}
+
+static uint64_t raidz_corrected_p;
+static uint64_t raidz_corrected_q;
+static uint64_t raidz_corrected_pq;
+
+static int
+vdev_raidz_worst_error(raidz_map_t *rm)
+{
+	int error = 0;
+
+	for (int c = 0; c < rm->rm_cols; c++)
+		error = zio_worst_error(error, rm->rm_col[c].rc_error);
+
+	return (error);
+}
+
+static void
+vdev_raidz_io_done(zio_t *zio)
+{
+	vdev_t *vd = zio->io_vd;
+	vdev_t *cvd;
+	raidz_map_t *rm = zio->io_vsd;
+	raidz_col_t *rc, *rc1;
+	int unexpected_errors = 0;
+	int parity_errors = 0;
+	int parity_untried = 0;
+	int data_errors = 0;
+	int total_errors = 0;
+	int n, c, c1;
+
+	ASSERT(zio->io_bp != NULL);  /* XXX need to add code to enforce this */
+
+	ASSERT(rm->rm_missingparity <= rm->rm_firstdatacol);
+	ASSERT(rm->rm_missingdata <= rm->rm_cols - rm->rm_firstdatacol);
+
+	for (c = 0; c < rm->rm_cols; c++) {
+		rc = &rm->rm_col[c];
+
+		if (rc->rc_error) {
+			ASSERT(rc->rc_error != ECKSUM);	/* child has no bp */
+
+			if (c < rm->rm_firstdatacol)
+				parity_errors++;
+			else
+				data_errors++;
+
+			if (!rc->rc_skipped)
+				unexpected_errors++;
+
+			total_errors++;
+		} else if (c < rm->rm_firstdatacol && !rc->rc_tried) {
+			parity_untried++;
+		}
+	}
+
+	if (zio->io_type == ZIO_TYPE_WRITE) {
+		/*
+		 * XXX -- for now, treat partial writes as a success.
+		 * (If we couldn't write enough columns to reconstruct
+		 * the data, the I/O failed.  Otherwise, good enough.)
+		 *
+		 * 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 (total_errors > rm->rm_firstdatacol)
+			zio->io_error = vdev_raidz_worst_error(rm);
+
+		return;
+	}
+
+	ASSERT(zio->io_type == ZIO_TYPE_READ);
+	/*
+	 * There are three potential phases for a read:
+	 *	1. produce valid data from the columns read
+	 *	2. read all disks and try again
+	 *	3. perform combinatorial reconstruction
+	 *
+	 * Each phase is progressively both more expensive and less likely to
+	 * occur. If we encounter more errors than we can repair or all phases
+	 * fail, we have no choice but to return an error.
+	 */
+
+	/*
+	 * If the number of errors we saw was correctable -- less than or equal
+	 * to the number of parity disks read -- attempt to produce data that
+	 * has a valid checksum. Naturally, this case applies in the absence of
+	 * any errors.
+	 */
+	if (total_errors <= rm->rm_firstdatacol - parity_untried) {
+		switch (data_errors) {
+		case 0:
+			if (zio_checksum_error(zio) == 0) {
+				/*
+				 * If we read parity information (unnecessarily
+				 * as it happens since no reconstruction was
+				 * needed) regenerate and verify the parity.
+				 * We also regenerate parity when resilvering
+				 * so we can write it out to the failed device
+				 * later.
+				 */
+				if (parity_errors + parity_untried <
+				    rm->rm_firstdatacol ||
+				    (zio->io_flags & ZIO_FLAG_RESILVER)) {
+					n = raidz_parity_verify(zio, rm);
+					unexpected_errors += n;
+					ASSERT(parity_errors + n <=
+					    rm->rm_firstdatacol);
+				}
+				goto done;
+			}
+			break;
+
+		case 1:
+			/*
+			 * We either attempt to read all the parity columns or
+			 * none of them. If we didn't try to read parity, we
+			 * wouldn't be here in the correctable case. There must
+			 * also have been fewer parity errors than parity
+			 * columns or, again, we wouldn't be in this code path.
+			 */
+			ASSERT(parity_untried == 0);
+			ASSERT(parity_errors < rm->rm_firstdatacol);
+
+			/*
+			 * Find the column that reported the error.
+			 */
+			for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+				rc = &rm->rm_col[c];
+				if (rc->rc_error != 0)
+					break;
+			}
+			ASSERT(c != rm->rm_cols);
+			ASSERT(!rc->rc_skipped || rc->rc_error == ENXIO ||
+			    rc->rc_error == ESTALE);
+
+			if (rm->rm_col[VDEV_RAIDZ_P].rc_error == 0) {
+				vdev_raidz_reconstruct_p(rm, c);
+			} else {
+				ASSERT(rm->rm_firstdatacol > 1);
+				vdev_raidz_reconstruct_q(rm, c);
+			}
+
+			if (zio_checksum_error(zio) == 0) {
+				if (rm->rm_col[VDEV_RAIDZ_P].rc_error == 0)
+					atomic_inc_64(&raidz_corrected_p);
+				else
+					atomic_inc_64(&raidz_corrected_q);
+
+				/*
+				 * If there's more than one parity disk that
+				 * was successfully read, confirm that the
+				 * other parity disk produced the correct data.
+				 * This routine is suboptimal in that it
+				 * regenerates both the parity we wish to test
+				 * as well as the parity we just used to
+				 * perform the reconstruction, but this should
+				 * be a relatively uncommon case, and can be
+				 * optimized if it becomes a problem.
+				 * We also regenerate parity when resilvering
+				 * so we can write it out to the failed device
+				 * later.
+				 */
+				if (parity_errors < rm->rm_firstdatacol - 1 ||
+				    (zio->io_flags & ZIO_FLAG_RESILVER)) {
+					n = raidz_parity_verify(zio, rm);
+					unexpected_errors += n;
+					ASSERT(parity_errors + n <=
+					    rm->rm_firstdatacol);
+				}
+
+				goto done;
+			}
+			break;
+
+		case 2:
+			/*
+			 * Two data column errors require double parity.
+			 */
+			ASSERT(rm->rm_firstdatacol == 2);
+
+			/*
+			 * Find the two columns that reported errors.
+			 */
+			for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+				rc = &rm->rm_col[c];
+				if (rc->rc_error != 0)
+					break;
+			}
+			ASSERT(c != rm->rm_cols);
+			ASSERT(!rc->rc_skipped || rc->rc_error == ENXIO ||
+			    rc->rc_error == ESTALE);
+
+			for (c1 = c++; c < rm->rm_cols; c++) {
+				rc = &rm->rm_col[c];
+				if (rc->rc_error != 0)
+					break;
+			}
+			ASSERT(c != rm->rm_cols);
+			ASSERT(!rc->rc_skipped || rc->rc_error == ENXIO ||
+			    rc->rc_error == ESTALE);
+
+			vdev_raidz_reconstruct_pq(rm, c1, c);
+
+			if (zio_checksum_error(zio) == 0) {
+				atomic_inc_64(&raidz_corrected_pq);
+				goto done;
+			}
+			break;
+
+		default:
+			ASSERT(rm->rm_firstdatacol <= 2);
+			ASSERT(0);
+		}
+	}
+
+	/*
+	 * This isn't a typical situation -- either we got a read error or
+	 * a child silently returned bad data. Read every block so we can
+	 * try again with as much data and parity as we can track down. If
+	 * we've already been through once before, all children will be marked
+	 * as tried so we'll proceed to combinatorial reconstruction.
+	 */
+	unexpected_errors = 1;
+	rm->rm_missingdata = 0;
+	rm->rm_missingparity = 0;
+
+	for (c = 0; c < rm->rm_cols; c++) {
+		if (rm->rm_col[c].rc_tried)
+			continue;
+
+		zio_vdev_io_redone(zio);
+		do {
+			rc = &rm->rm_col[c];
+			if (rc->rc_tried)
+				continue;
+			zio_nowait(zio_vdev_child_io(zio, NULL,
+			    vd->vdev_child[rc->rc_devidx],
+			    rc->rc_offset, rc->rc_data, rc->rc_size,
+			    zio->io_type, zio->io_priority, 0,
+			    vdev_raidz_child_done, rc));
+		} while (++c < rm->rm_cols);
+
+		return;
+	}
+
+	/*
+	 * At this point we've attempted to reconstruct the data given the
+	 * errors we detected, and we've attempted to read all columns. There
+	 * must, therefore, be one or more additional problems -- silent errors
+	 * resulting in invalid data rather than explicit I/O errors resulting
+	 * in absent data. Before we attempt combinatorial reconstruction make
+	 * sure we have a chance of coming up with the right answer.
+	 */
+	if (total_errors >= rm->rm_firstdatacol) {
+		zio->io_error = vdev_raidz_worst_error(rm);
+		/*
+		 * If there were exactly as many device errors as parity
+		 * columns, yet we couldn't reconstruct the data, then at
+		 * least one device must have returned bad data silently.
+		 */
+		if (total_errors == rm->rm_firstdatacol)
+			zio->io_error = zio_worst_error(zio->io_error, ECKSUM);
+		goto done;
+	}
+
+	if (rm->rm_col[VDEV_RAIDZ_P].rc_error == 0) {
+		/*
+		 * Attempt to reconstruct the data from parity P.
+		 */
+		for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+			void *orig;
+			rc = &rm->rm_col[c];
+
+			orig = zio_buf_alloc(rc->rc_size);
+			bcopy(rc->rc_data, orig, rc->rc_size);
+			vdev_raidz_reconstruct_p(rm, c);
+
+			if (zio_checksum_error(zio) == 0) {
+				zio_buf_free(orig, rc->rc_size);
+				atomic_inc_64(&raidz_corrected_p);
+
+				/*
+				 * If this child didn't know that it returned
+				 * bad data, inform it.
+				 */
+				if (rc->rc_tried && rc->rc_error == 0)
+					raidz_checksum_error(zio, rc);
+				rc->rc_error = ECKSUM;
+				goto done;
+			}
+
+			bcopy(orig, rc->rc_data, rc->rc_size);
+			zio_buf_free(orig, rc->rc_size);
+		}
+	}
+
+	if (rm->rm_firstdatacol > 1 && rm->rm_col[VDEV_RAIDZ_Q].rc_error == 0) {
+		/*
+		 * Attempt to reconstruct the data from parity Q.
+		 */
+		for (c = rm->rm_firstdatacol; c < rm->rm_cols; c++) {
+			void *orig;
+			rc = &rm->rm_col[c];
+
+			orig = zio_buf_alloc(rc->rc_size);
+			bcopy(rc->rc_data, orig, rc->rc_size);
+			vdev_raidz_reconstruct_q(rm, c);
+
+			if (zio_checksum_error(zio) == 0) {
+				zio_buf_free(orig, rc->rc_size);
+				atomic_inc_64(&raidz_corrected_q);
+
+				/*
+				 * If this child didn't know that it returned
+				 * bad data, inform it.
+				 */
+				if (rc->rc_tried && rc->rc_error == 0)
+					raidz_checksum_error(zio, rc);
+				rc->rc_error = ECKSUM;
+				goto done;
+			}
+
+			bcopy(orig, rc->rc_data, rc->rc_size);
+			zio_buf_free(orig, rc->rc_size);
+		}
+	}
+
+	if (rm->rm_firstdatacol > 1 &&
+	    rm->rm_col[VDEV_RAIDZ_P].rc_error == 0 &&
+	    rm->rm_col[VDEV_RAIDZ_Q].rc_error == 0) {
+		/*
+		 * Attempt to reconstruct the data from both P and Q.
+		 */
+		for (c = rm->rm_firstdatacol; c < rm->rm_cols - 1; c++) {
+			void *orig, *orig1;
+			rc = &rm->rm_col[c];
+
+			orig = zio_buf_alloc(rc->rc_size);
+			bcopy(rc->rc_data, orig, rc->rc_size);
+
+			for (c1 = c + 1; c1 < rm->rm_cols; c1++) {
+				rc1 = &rm->rm_col[c1];
+
+				orig1 = zio_buf_alloc(rc1->rc_size);
+				bcopy(rc1->rc_data, orig1, rc1->rc_size);
+
+				vdev_raidz_reconstruct_pq(rm, c, c1);
+
+				if (zio_checksum_error(zio) == 0) {
+					zio_buf_free(orig, rc->rc_size);
+					zio_buf_free(orig1, rc1->rc_size);
+					atomic_inc_64(&raidz_corrected_pq);
+
+					/*
+					 * If these children didn't know they
+					 * returned bad data, inform them.
+					 */
+					if (rc->rc_tried && rc->rc_error == 0)
+						raidz_checksum_error(zio, rc);
+					if (rc1->rc_tried && rc1->rc_error == 0)
+						raidz_checksum_error(zio, rc1);
+
+					rc->rc_error = ECKSUM;
+					rc1->rc_error = ECKSUM;
+
+					goto done;
+				}
+
+				bcopy(orig1, rc1->rc_data, rc1->rc_size);
+				zio_buf_free(orig1, rc1->rc_size);
+			}
+
+			bcopy(orig, rc->rc_data, rc->rc_size);
+			zio_buf_free(orig, rc->rc_size);
+		}
+	}
+
+	/*
+	 * All combinations failed to checksum. Generate checksum ereports for
+	 * all children.
+	 */
+	zio->io_error = ECKSUM;
+
+	if (!(zio->io_flags & ZIO_FLAG_SPECULATIVE)) {
+		for (c = 0; c < rm->rm_cols; c++) {
+			rc = &rm->rm_col[c];
+			zfs_ereport_post(FM_EREPORT_ZFS_CHECKSUM,
+			    zio->io_spa, vd->vdev_child[rc->rc_devidx], zio,
+			    rc->rc_offset, rc->rc_size);
+		}
+	}
+
+done:
+	zio_checksum_verified(zio);
+
+	if (zio->io_error == 0 && (spa_mode & FWRITE) &&
+	    (unexpected_errors || (zio->io_flags & ZIO_FLAG_RESILVER))) {
+		/*
+		 * Use the good data we have in hand to repair damaged children.
+		 */
+		for (c = 0; c < rm->rm_cols; c++) {
+			rc = &rm->rm_col[c];
+			cvd = vd->vdev_child[rc->rc_devidx];
+
+			if (rc->rc_error == 0)
+				continue;
+
+			zio_nowait(zio_vdev_child_io(zio, NULL, cvd,
+			    rc->rc_offset, rc->rc_data, rc->rc_size,
+			    ZIO_TYPE_WRITE, zio->io_priority,
+			    ZIO_FLAG_IO_REPAIR, NULL, NULL));
+		}
+	}
+}
+
+static void
+vdev_raidz_state_change(vdev_t *vd, int faulted, int degraded)
+{
+	if (faulted > vd->vdev_nparity)
+		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_raidz_ops = {
+	vdev_raidz_open,
+	vdev_raidz_close,
+	vdev_raidz_asize,
+	vdev_raidz_io_start,
+	vdev_raidz_io_done,
+	vdev_raidz_state_change,
+	VDEV_TYPE_RAIDZ,	/* name of this vdev type */
+	B_FALSE			/* not a leaf vdev */
+};