forked from Minki/linux
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: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
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@ -550,6 +550,13 @@ static void __raid10_find_phys(struct geom *geo, struct r10bio *r10bio)
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sector_t stripe;
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int dev;
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int slot = 0;
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int last_far_set_start, last_far_set_size;
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last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;
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last_far_set_start *= geo->far_set_size;
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last_far_set_size = geo->far_set_size;
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last_far_set_size += (geo->raid_disks % geo->far_set_size);
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/* now calculate first sector/dev */
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chunk = r10bio->sector >> geo->chunk_shift;
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@ -575,9 +582,16 @@ static void __raid10_find_phys(struct geom *geo, struct r10bio *r10bio)
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for (f = 1; f < geo->far_copies; f++) {
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set = d / geo->far_set_size;
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d += geo->near_copies;
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d %= geo->far_set_size;
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d += geo->far_set_size * set;
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if ((geo->raid_disks % geo->far_set_size) &&
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(d > last_far_set_start)) {
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d -= last_far_set_start;
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d %= last_far_set_size;
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d += last_far_set_start;
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} else {
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d %= geo->far_set_size;
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d += geo->far_set_size * set;
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}
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s += geo->stride;
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r10bio->devs[slot].devnum = d;
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r10bio->devs[slot].addr = s;
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@ -615,6 +629,18 @@ static sector_t raid10_find_virt(struct r10conf *conf, sector_t sector, int dev)
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struct geom *geo = &conf->geo;
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int far_set_start = (dev / geo->far_set_size) * geo->far_set_size;
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int far_set_size = geo->far_set_size;
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int last_far_set_start;
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if (geo->raid_disks % geo->far_set_size) {
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last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;
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last_far_set_start *= geo->far_set_size;
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if (dev >= last_far_set_start) {
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far_set_size = geo->far_set_size;
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far_set_size += (geo->raid_disks % geo->far_set_size);
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far_set_start = last_far_set_start;
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}
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}
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offset = sector & geo->chunk_mask;
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if (geo->far_offset) {
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