diff -pur linux-2.6.18-53.orig/drivers/md/raid5.c linux-2.6.18-53/drivers/md/raid5.c
--- linux-2.6.18-53.orig/drivers/md/raid5.c	2007-12-06 17:26:27.000000000 +0800
+++ linux-2.6.18-53/drivers/md/raid5.c	2007-12-06 17:26:55.000000000 +0800
@@ -3340,6 +3340,11 @@ static int run(mddev_t *mddev)
 	mddev->array_size =  mddev->size * (conf->previous_raid_disks -
 					    conf->max_degraded);
 
+	/* in order to support large I/Os */
+	blk_queue_max_sectors(mddev->queue, conf->chunk_size * conf->previous_raid_disks >> 9);
+	mddev->queue->max_phys_segments = conf->chunk_size * conf->previous_raid_disks >> PAGE_SHIFT;
+	mddev->queue->max_hw_segments = conf->chunk_size * conf->previous_raid_disks >> PAGE_SHIFT;;
+
 	return 0;
 abort:
 	if (conf) {