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Commit 4e5314b5 authored by NeilBrown's avatar NeilBrown Committed by Linus Torvalds
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[PATCH] md: better handling of readerrors with raid5. 



This patch changes the behaviour of raid5 when it gets a read error.
Instead of just failing the device, it tried to find out what should have
been there, and writes it over the bad block.  For some media-errors, this
has a reasonable chance of fixing the error.  If the write succeeds, and a
subsequent read succeeds as well, raid5 decided the address is OK and
conitnues.

Instead of failing a drive on read-error, we attempt to re-write the block,
and then re-read.  If that all works, we allow the device to remain in the
array.

Signed-off-by: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 703ebe86

drivers/md/raid5.c

+56 −5
Original line number Diff line number Diff line
@@ -402,9 +402,26 @@ static int raid5_end_read_request (struct bio * bi, unsigned int bytes_done, 
#else

		set_bit(R5_UPTODATE, &sh->dev[i].flags);

#endif

		if (test_bit(R5_ReadError, &sh->dev[i].flags)) {

			printk("R5: read error corrected!!\n");

			clear_bit(R5_ReadError, &sh->dev[i].flags);

			clear_bit(R5_ReWrite, &sh->dev[i].flags);

		}

	} else {

		md_error(conf->mddev, conf->disks[i].rdev);

		clear_bit(R5_UPTODATE, &sh->dev[i].flags);

		if (conf->mddev->degraded) {

			printk("R5: read error not correctable.\n");

			clear_bit(R5_ReadError, &sh->dev[i].flags);

			clear_bit(R5_ReWrite, &sh->dev[i].flags);

			md_error(conf->mddev, conf->disks[i].rdev);

		} else if (test_bit(R5_ReWrite, &sh->dev[i].flags)) {

			/* Oh, no!!! */

			printk("R5: read error NOT corrected!!\n");

			clear_bit(R5_ReadError, &sh->dev[i].flags);

			clear_bit(R5_ReWrite, &sh->dev[i].flags);

			md_error(conf->mddev, conf->disks[i].rdev);

		} else

			set_bit(R5_ReadError, &sh->dev[i].flags);

	}

	rdev_dec_pending(conf->disks[i].rdev, conf->mddev);

#if 0
@@ -966,6 +983,12 @@ static void handle_stripe(struct stripe_head *sh) 
		if (dev->written) written++;

		rdev = conf->disks[i].rdev; /* FIXME, should I be looking rdev */

		if (!rdev || !rdev->in_sync) {

			/* The ReadError flag wil just be confusing now */

			clear_bit(R5_ReadError, &dev->flags);

			clear_bit(R5_ReWrite, &dev->flags);

		}

		if (!rdev || !rdev->in_sync

		    || test_bit(R5_ReadError, &dev->flags)) {

			failed++;

			failed_num = i;

		} else
@@ -980,6 +1003,14 @@ static void handle_stripe(struct stripe_head *sh) 
	if (failed > 1 && to_read+to_write+written) {

		for (i=disks; i--; ) {

			int bitmap_end = 0;



			if (test_bit(R5_ReadError, &sh->dev[i].flags)) {

				mdk_rdev_t *rdev = conf->disks[i].rdev;

				if (rdev && rdev->in_sync)

					/* multiple read failures in one stripe */

					md_error(conf->mddev, rdev);

			}



			spin_lock_irq(&conf->device_lock);

			/* fail all writes first */

			bi = sh->dev[i].towrite;
@@ -1015,7 +1046,8 @@ static void handle_stripe(struct stripe_head *sh) 
			}



			/* fail any reads if this device is non-operational */

			if (!test_bit(R5_Insync, &sh->dev[i].flags)) {

			if (!test_bit(R5_Insync, &sh->dev[i].flags) ||

			    test_bit(R5_ReadError, &sh->dev[i].flags)) {

				bi = sh->dev[i].toread;

				sh->dev[i].toread = NULL;

				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
@@ -1275,6 +1307,25 @@ static void handle_stripe(struct stripe_head *sh) 
		clear_bit(STRIPE_SYNCING, &sh->state);

	}



	/* If the failed drive is just a ReadError, then we might need to progress

	 * the repair/check process

	 */

	if (failed == 1 && test_bit(R5_ReadError, &sh->dev[failed_num].flags)

	    && !test_bit(R5_LOCKED, &sh->dev[failed_num].flags)

	    && test_bit(R5_UPTODATE, &sh->dev[failed_num].flags)

		) {

		dev = &sh->dev[failed_num];

		if (!test_bit(R5_ReWrite, &dev->flags)) {

			set_bit(R5_Wantwrite, &dev->flags);

			set_bit(R5_ReWrite, &dev->flags);

			set_bit(R5_LOCKED, &dev->flags);

		} else {

			/* let's read it back */

			set_bit(R5_Wantread, &dev->flags);

			set_bit(R5_LOCKED, &dev->flags);

		}

	}



	spin_unlock(&sh->lock);



	while ((bi=return_bi)) {

include/linux/raid/raid5.h

+2 −0
Original line number Diff line number Diff line
@@ -154,6 +154,8 @@ struct stripe_head { 
#define	R5_Wantwrite	5

#define	R5_Syncio	6	/* this io need to be accounted as resync io */

#define	R5_Overlap	7	/* There is a pending overlapping request on this block */

#define	R5_ReadError	8	/* seen a read error here recently */

#define	R5_ReWrite	9	/* have tried to over-write the readerror */



/*

 * Write method