Commit 8bce6d35 authored by NeilBrown's avatar NeilBrown
Browse files

md/raid10: fix the 'new' raid10 layout to work correctly. 



In Linux 3.9 we introduce a new 'far' layout for RAID10 which was
supposed to rotate the replicas differently and so provide better
resilience.  In particular it could survive more combinations of 2
drive failures.

Unfortunately. due to a coding error, this some did what was wanted,
sometimes improved less than we hoped, and sometimes - in very
unlikely circumstances - put multiple replicas on the same device so
the redundancy was harmed.

No public user-space tool has created arrays using this layout so it
is very unlikely that zero-redundancy arrays actually exist.  Probably
no arrays using any form of the new layout exist.  But we cannot be
certain.

So use another bit in the 'layout' number and introduce a bug-fixed
version of the layout.
Also when assembling an array, if it has a zero-redundancy layout,
give a warning.

Reported-by: default avatarHeinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
parent c340702c

drivers/md/raid10.c

+20 −2
Original line number Diff line number Diff line
@@ -39,6 +39,7 @@ 
 *    far_copies (stored in second byte of layout)

 *    far_offset (stored in bit 16 of layout )

 *    use_far_sets (stored in bit 17 of layout )

 *    use_far_sets_bugfixed (stored in bit 18 of layout )

 *

 * The data to be stored is divided into chunks using chunksize.  Each device

 * is divided into far_copies sections.   In each section, chunks are laid out
@@ -1497,6 +1498,8 @@ static void status(struct seq_file *seq, struct mddev *mddev) 
			seq_printf(seq, " %d offset-copies", conf->geo.far_copies);

		else

			seq_printf(seq, " %d far-copies", conf->geo.far_copies);

		if (conf->geo.far_set_size != conf->geo.raid_disks)

			seq_printf(seq, " %d devices per set", conf->geo.far_set_size);

	}

	seq_printf(seq, " [%d/%d] [", conf->geo.raid_disks,

					conf->geo.raid_disks - mddev->degraded);
@@ -3394,7 +3397,7 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new) 
		disks = mddev->raid_disks + mddev->delta_disks;

		break;

	}

	if (layout >> 18)

	if (layout >> 19)

		return -1;

	if (chunk < (PAGE_SIZE >> 9) ||

	    !is_power_of_2(chunk))
@@ -3406,7 +3409,22 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new) 
	geo->near_copies = nc;

	geo->far_copies = fc;

	geo->far_offset = fo;

	geo->far_set_size = (layout & (1<<17)) ? disks / fc : disks;

	switch (layout >> 17) {

	case 0:	/* original layout.  simple but not always optimal */

		geo->far_set_size = disks;

		break;

	case 1: /* "improved" layout which was buggy.  Hopefully no-one is

		 * actually using this, but leave code here just in case.*/

		geo->far_set_size = disks/fc;

		WARN(geo->far_set_size < fc,

		     "This RAID10 layout does not provide data safety - please backup and create new array\n");

		break;

	case 2: /* "improved" layout fixed to match documentation */

		geo->far_set_size = fc * nc;

		break;

	default: /* Not a valid layout */

		return -1;

	}

	geo->chunk_mask = chunk - 1;

	geo->chunk_shift = ffz(~chunk);

	return nc*fc;

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