Commit 9a3152ab authored by Jonathan Brassow's avatar Jonathan Brassow Committed by NeilBrown
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MD RAID10: Improve redundancy for 'far' and 'offset' algorithms (part 2) 



MD RAID10:  Improve redundancy for 'far' and 'offset' algorithms (part 2)

This patch addresses raid arrays that have a number of devices that cannot
be evenly divided by 'far_copies'.  (E.g. 5 devices, far_copies = 2)  This
case must be handled differently because it causes that last set to be of
a different size than the rest of the sets.  We must compute a new modulo
for this last set so that copied chunks are properly wrapped around.

Example use_far_sets=1, far_copies=2, near_copies=1, devices=5:
                "far" algorithm
        dev1 dev2 dev3 dev4 dev5
	==== ==== ==== ==== ====
	[ A   B ] [ C    D   E ]
        [ G   H ] [ I    J   K ]
                    ...
        [ B   A ] [ E    C   D ] --> nominal set of 2 and last set of 3
        [ H   G ] [ K    I   J ]     []'s show far/offset sets

Signed-off-by: default avatarJonathan Brassow <jbrassow@redhat.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 475901af

drivers/md/raid10.c

+28 −2
Original line number Diff line number Diff line
@@ -550,6 +550,13 @@ static void __raid10_find_phys(struct geom *geo, struct r10bio *r10bio) 
	sector_t stripe;

	int dev;

	int slot = 0;

	int last_far_set_start, last_far_set_size;



	last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;

	last_far_set_start *= geo->far_set_size;



	last_far_set_size = geo->far_set_size;

	last_far_set_size += (geo->raid_disks % geo->far_set_size);



	/* now calculate first sector/dev */

	chunk = r10bio->sector >> geo->chunk_shift;
@@ -575,9 +582,16 @@ static void __raid10_find_phys(struct geom *geo, struct r10bio *r10bio) 
		for (f = 1; f < geo->far_copies; f++) {

			set = d / geo->far_set_size;

			d += geo->near_copies;



			if ((geo->raid_disks % geo->far_set_size) &&

			    (d > last_far_set_start)) {

				d -= last_far_set_start;

				d %= last_far_set_size;

				d += last_far_set_start;

			} else {

				d %= geo->far_set_size;

				d += geo->far_set_size * set;



			}

			s += geo->stride;

			r10bio->devs[slot].devnum = d;

			r10bio->devs[slot].addr = s;
@@ -615,6 +629,18 @@ static sector_t raid10_find_virt(struct r10conf *conf, sector_t sector, int dev) 
	struct geom *geo = &conf->geo;

	int far_set_start = (dev / geo->far_set_size) * geo->far_set_size;

	int far_set_size = geo->far_set_size;

	int last_far_set_start;



	if (geo->raid_disks % geo->far_set_size) {

		last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;

		last_far_set_start *= geo->far_set_size;



		if (dev >= last_far_set_start) {

			far_set_size = geo->far_set_size;

			far_set_size += (geo->raid_disks % geo->far_set_size);

			far_set_start = last_far_set_start;

		}

	}



	offset = sector & geo->chunk_mask;

	if (geo->far_offset) {

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