Copie sur écriture, sommes de contrôle et autoréparation

	/*
	 * The final pass of spa_sync() must be all rewrites, but the first
	 * few passes offer a trade-off: allocating blocks defers convergence,
	 * but newly allocated blocks are sequential, so they can be written
	 * to disk faster.  Therefore, we allow the first few passes of
	 * spa_sync() to allocate new blocks, but force rewrites after that.
	 * There should only be a handful of blocks after pass 1 in any case.
	 */
	if (!BP_IS_HOLE(bp) && BP_GET_BIRTH(bp) == zio->io_txg &&
	    BP_GET_PSIZE(bp) == psize &&
	    pass >= zfs_sync_pass_rewrite) {
		VERIFY3U(psize, !=, 0);
		enum zio_stage gang_stages = zio->io_pipeline & ZIO_GANG_STAGES;

		zio->io_pipeline = ZIO_REWRITE_PIPELINE | gang_stages;
		zio->io_flags |= ZIO_FLAG_IO_REWRITE;
	} else {
		BP_ZERO(bp);
		zio->io_pipeline = ZIO_WRITE_PIPELINE;
	}

	} else {
		byteswap = BP_SHOULD_BYTESWAP(bp);
		expected_cksum = bp->blk_cksum;
		ci->ci_func[byteswap](abd, size,
		    spa->spa_cksum_tmpls[checksum], &actual_cksum);
	}

	/*
	 * MAC checksums are a special case since half of this checksum will
	 * actually be the encryption MAC. This will be verified by the
	 * decryption process, so we just check the truncated checksum now.
	 * Objset blocks use embedded MACs so we don't truncate the checksum
	 * for them.
	 */
	if (bp != NULL && BP_USES_CRYPT(bp) &&
	    BP_GET_TYPE(bp) != DMU_OT_OBJSET) {
		if (!(ci->ci_flags & ZCHECKSUM_FLAG_DEDUP)) {
			actual_cksum.zc_word[0] ^= actual_cksum.zc_word[2];
			actual_cksum.zc_word[1] ^= actual_cksum.zc_word[3];
		}

		actual_cksum.zc_word[2] = 0;
		actual_cksum.zc_word[3] = 0;
		expected_cksum.zc_word[2] = 0;
		expected_cksum.zc_word[3] = 0;
	}

	if (info != NULL) {
		info->zbc_checksum_name = ci->ci_name;
		info->zbc_byteswapped = byteswap;
		info->zbc_injected = 0;
		info->zbc_has_cksum = 1;
	}

	if (!ZIO_CHECKSUM_EQUAL(actual_cksum, expected_cksum))
		return (SET_ERROR(ECKSUM));

	return (0);

			if (mc->mc_error == 0) {
				vdev_ops_t *ops = mc->mc_vd->vdev_ops;

				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 or distributed spare
				 * 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) &&
				    ops != &vdev_indirect_ops &&
				    ops != &vdev_draid_spare_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->io_priority == ZIO_PRIORITY_REBUILD ?
			    ZIO_PRIORITY_REBUILD : ZIO_PRIORITY_ASYNC_WRITE,
			    ZIO_FLAG_IO_REPAIR | (unexpected_errors ?
			    ZIO_FLAG_SELF_HEAL : 0), NULL, NULL));
		}