On Fri, 10 Apr 2015 11:31:57 +1000 Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Fri, Apr 10, 2015 at 09:36:52AM +1000, NeilBrown wrote: > > On Fri, 10 Apr 2015 09:10:35 +1000 Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > > > On Fri, Apr 10, 2015 at 08:53:22AM +1000, Dave Chinner wrote: > > > > On Thu, Apr 09, 2015 at 06:20:26PM -0400, Joe Landman wrote: > > > > > > > > > > > > > > > On 04/09/2015 06:18 PM, Dave Chinner wrote: > > > > > >On Thu, Apr 09, 2015 at 05:02:33PM -0400, Joe Landman wrote: > > > > > >>If I build an MD raid0 with a non power of 2 chunk size, it appears > > > > > >>that I can mkfs.xfs a file system, but it doesn't show up in blkid > > > > > >>and is not mountable. Yet, using a power of 2 chunk size, this does > > > > > >>work correctly. This is kernel 3.18.9. > > > > > >> > > > > > > > > > > [...] > > > > > > > > > > >That looks more like a blkid or udev problem. try using blkid -p so > > > > > >that it doesn't look up the cache but directly probes devices for > > > > > >the signatures. strace might tell you a bit more, too. And if the > > > > > >filesystem mounts, then it definitely isn't an XFS problem ;) > > > > > > > > > > Thats the thing, it didn't mount, even when I used the device name > > > > > directly. > > > > > > > > Ok, that's interesting. Let me see if I can reproduce it locally. If > > > > you don't hear otherwise, tracing would still be useful. Thanks for > > > > the bug report, Joe. > > > > > > No luck - md doesn't allow the device to be activated on 4.0-rc7: > > > > > > $ sudo mdadm --version > > > mdadm - v3.3.2 - 21st August 2014 > > > $ uname -a > > > Linux test4 4.0.0-rc7-dgc+ #882 SMP Fri Apr 10 08:50:52 AEST 2015 x86_64 GNU/Linux > > > $ sudo wipefs -a /dev/vd[ab] > > > /dev/vda: 4 bytes were erased at offset 0x00001000 (linux_raid_member): fc 4e 2b a9 > > > /dev/vdb: 4 bytes were erased at offset 0x00001000 (linux_raid_member): fc 4e 2b a9 > > > $ sudo mdadm --create /dev/md20 --level=0 --metadata=1.2 --chunk=1152 --auto=yes --raid-disks=2 /dev/vd[ab] > > > > Weird. Works for me. > > Any messages in 'dmesg' ?? > > How big are /dev/vd[ab]?? > > vda is 5GB, vdb is 20GB > > dmesg: > > [ 125.131340] md: bind<vda> > [ 125.134547] md: bind<vdb> > [ 125.139669] md: personality for level 0 is not loaded! > [ 125.141302] md: md20 stopped. > [ 125.141986] md: unbind<vdb> > [ 125.160100] md: export_rdev(vdb) > [ 125.161751] md: unbind<vda> > [ 125.180126] md: export_rdev(vda) > > Oh, curious. Going from 4.0-rc4 to 4.0-rc7, and make oldconfig > has resulted in: > > # CONFIG_MD_RAID0 is not set > > Ok, so with that fixed, it's still horribly broken. > > RAID 0 on different sized devices should result in a device that is > twice the size of the smallest devices: > > $ sudo mdadm --create /dev/md20 --level=raid0 --metadata=1.2 --chunk=1024 --auto=yes --raid-disks=2 /dev/vd[ab] > mdadm: array /dev/md20 started. > $ cat /proc/mdstat > Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] > md20 : active raid0 vdb[1] vda[0] > 26206208 blocks super 1.2 1024k chunks > > unused devices: <none> > $ grep "md\|vd[ab]" /proc/partitions > 253 0 5242880 vda > 253 16 20971520 vdb > 9 20 26206208 md20 > $ > > Oh, "RAID0" is not actually RAID 0 - that's the size I'd expect from > a linear mapping. Half way through writing that block device, the IO > stats change in an obvious way: > > Device: r/s w/s rMB/s wMB/s > vda 0.00 144.00 0.00 48.00 > vdb 0.00 145.20 0.00 48.40 > md20 0.00 290.40 0.00 96.80 > > Device: r/s w/s rMB/s wMB/s > vda 0.00 56.40 0.00 18.80 > vdb 0.00 229.20 0.00 76.40 > md20 0.00 285.20 0.00 95.10 > > Device: r/s w/s rMB/s wMB/s > vda 0.00 0.00 0.00 0.00 > vdb 0.00 290.40 0.00 96.80 > md20 0.00 290.80 0.00 96.90 > > So it's actually a stripe for the first 10GB, then some kind of > concatenated mapping of the remainder of the single device. That's > not what I expected, but it's also clearly not the problem. > > Anyway, change the stripe size to 1152: > > sudo mdadm --stop /dev/md20 > mdadm: stopped /dev/md20 > $ sudo wipefs -a /dev/vd[ab] > /dev/vda: 4 bytes were erased at offset 0x00001000 (linux_raid_member): fc 4e 2b a9 > /dev/vdb: 4 bytes were erased at offset 0x00001000 (linux_raid_member): fc 4e 2b a9 > $ sudo mdadm --create /dev/md20 --level=raid0 --metadata=1.2 --chunk=1152 --auto=yes --raid-disks=2 /dev/vd[ab] > mdadm: array /dev/md20 started. > $ sudo xfs_io -fd -c "pwrite -b 4m 0 25g" /dev/md20 > wrote 26831355904/26843545600 bytes at offset 0 > 24.989 GiB, 6398 ops; 0:00:16.00 (1.530 GiB/sec and 391.8556 ops/sec) > $ > > Wait, what? Neil, did you put a flux capacitor in MD? :P > > The underlying drive is only capable of 100MB/s - 25GB of sequential > direct IO does not complete in 16 seconds on such a drive. But > there's also a 1GB BBWC in front of the physical drives (HW RAID1), > but even so, this write rate could only occur if every write is > hitting the BBWC. And so it is: > > $ sudo xfs_io -fd -c "pwrite -b 4m 0 25g" /dev/md20 & iostat -d -m 1 > ... > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > vda 4214.00 0.00 1516.99 0 1516 > vdb 0.00 0.00 0.00 0 0 > md20 4223.00 0.00 1520.00 0 1520 > > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > vda 2986.00 0.00 1075.01 0 1075 > vdb 1174.00 0.00 422.88 0 422 > md20 4154.00 0.00 1496.00 0 1496 > > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > vda 0.00 0.00 0.00 0 0 > vdb 4376.00 0.00 1575.12 0 1575 > md20 4378.00 0.00 1576.00 0 1576 > > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > vda 2682.00 0.00 965.74 0 965 > vdb 1650.00 0.00 594.00 0 594 > md20 4334.00 0.00 1560.00 0 1560 > > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > vda 4518.00 0.00 1626.26 0 1626 > vdb 138.00 0.00 49.50 0 49 > md20 4656.00 0.00 1676.00 0 1676 > > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > vda 0.00 0.00 0.00 0 0 > vdb 4214.00 0.00 1517.48 0 1517 > md20 4210.00 0.00 1516.00 0 1516 > ..... > > Note how it is cycling from one drive to the other with about a 2s > period? > > Yup, blocktrace on /dev/vda shows it is, indeed, hitting the BBWC > because the block mapping is clearly broken: > > 253,0 4 1 0.000000000 6972 Q WS 8192 + 1008 [xfs_io] > 253,0 4 5 0.000068012 6972 Q WS 8192 + 1008 [xfs_io] > 253,0 4 9 0.000093266 6972 Q WS 8192 + 288 [xfs_io] > 253,0 4 13 0.000129722 6972 Q WS 8193 + 1008 [xfs_io] > 253,0 4 17 0.000176872 6972 Q WS 8193 + 1008 [xfs_io] > 253,0 4 21 0.000205566 6972 Q WS 8193 + 288 [xfs_io] > 253,0 4 25 0.000240846 6972 Q WS 8194 + 1008 [xfs_io] > 253,0 4 29 0.000284990 6972 Q WS 8194 + 1008 [xfs_io] > 253,0 4 33 0.000313276 6972 Q WS 8194 + 288 [xfs_io] > 253,0 4 37 0.000352330 6972 Q WS 8195 + 1008 [xfs_io] > 253,0 4 41 0.000374272 6972 Q WS 8195 + 272 [xfs_io] > 253,0 4 56 0.001215857 6972 Q WS 8195 + 1008 [xfs_io] > 253,0 4 60 0.001252697 6972 Q WS 8195 + 16 [xfs_io] > 253,0 4 64 0.001284517 6972 Q WS 8196 + 1008 [xfs_io] > 253,0 4 68 0.001326130 6972 Q WS 8196 + 1008 [xfs_io] > 253,0 4 72 0.001355050 6972 Q WS 8196 + 288 [xfs_io] > 253,0 4 76 0.001393777 6972 Q WS 8197 + 1008 [xfs_io] > 253,0 4 80 0.001439547 6972 Q WS 8197 + 1008 [xfs_io] > 253,0 4 84 0.001466097 6972 Q WS 8197 + 288 [xfs_io] > 253,0 4 88 0.001501267 6972 Q WS 8198 + 1008 [xfs_io] > 253,0 4 92 0.001545863 6972 Q WS 8198 + 1008 [xfs_io] > 253,0 4 96 0.001571500 6972 Q WS 8198 + 288 [xfs_io] > 253,0 4 100 0.001584620 6972 Q WS 8199 + 256 [xfs_io] > 253,0 4 116 0.002730034 6972 Q WS 8199 + 1008 [xfs_io] > 253,0 4 120 0.002792351 6972 Q WS 8199 + 1008 [xfs_io] > 253,0 4 124 0.002810937 6972 Q WS 8199 + 32 [xfs_io] > 253,0 4 128 0.002842047 6972 Q WS 8200 + 1008 [xfs_io] > 253,0 4 132 0.002889087 6972 Q WS 8200 + 1008 [xfs_io] > 253,0 4 136 0.002916894 6972 Q WS 8200 + 288 [xfs_io] > 253,0 4 140 0.002952334 6972 Q WS 8201 + 1008 [xfs_io] > 253,0 4 144 0.002996101 6972 Q WS 8201 + 1008 [xfs_io] > 253,0 4 148 0.003022401 6972 Q WS 8201 + 288 [xfs_io] > > > Multiple IOs to teh same sector, then the sector increments by 1 and > we get more IOs to the same sector offset. After about a second the > mapping shifts IO to the other block device as it slowly increments > the sector, and that's why we see that cycling behaviour. > > IOWs, something is going wrong with the MD block mapping when the > RAID chunk size is not a power of 2.... > > Over to you, Neil.... That's .... not good. Not good at all. This should help. It seems that non-power-of-2 chunksizes aren't widely used. Thanks, NeilBrown From: NeilBrown <neilb@xxxxxxx> Date: Fri, 10 Apr 2015 13:19:04 +1000 Subject: [PATCH] md/raid0: fix bug with chunksize not a power of 2. Since commit 20d0189b1012a37d2533a87fb451f7852f2418d1 in v3.14-rc1 RAID0 has performed incorrect calculations when the chunksize is not a power of 2. This happens because "sector_div()" modifies its first argument, but this wasn't taken into account in the patch. So restore that first arg before re-using the variable. Reported-by: Joe Landman <joe.landman@xxxxxxxxx> Reported-by: Dave Chinner <david@xxxxxxxxxxxxx> Fixes: 20d0189b1012a37d2533a87fb451f7852f2418d1 Cc: stable@xxxxxxxxxxxxxxx (3.14 and later). Signed-off-by: NeilBrown <neilb@xxxxxxx> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c index e074813da6c0..2cb59a641cd2 100644 --- a/drivers/md/raid0.c +++ b/drivers/md/raid0.c @@ -315,7 +315,7 @@ static struct strip_zone *find_zone(struct r0conf *conf, /* * remaps the bio to the target device. we separate two flows. - * power 2 flow and a general flow for the sake of perfromance + * power 2 flow and a general flow for the sake of performance */ static struct md_rdev *map_sector(struct mddev *mddev, struct strip_zone *zone, sector_t sector, sector_t *sector_offset) @@ -530,6 +530,7 @@ static void raid0_make_request(struct mddev *mddev, struct bio *bio) split = bio; } + sector = bio->bi_iter.bi_sector; zone = find_zone(mddev->private, §or); tmp_dev = map_sector(mddev, zone, sector, §or); split->bi_bdev = tmp_dev->bdev;
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