On Wed, 15 Oct 2014 09:13:08 -0400 Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Tue, Oct 14 2014 at 11:40pm -0400, > NeilBrown <neilb@xxxxxxx> wrote: > > > On Tue, 14 Oct 2014 22:55:50 -0400 Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > > > > On Tue, Oct 14 2014 at 9:19pm -0400, > > > NeilBrown <neilb@xxxxxxx> wrote: > > > > > > > > > > > dm_raid_superblock is 512. > > > > Reading or writing this on a 512-byte sector works fine. > > > > On a 4096-byte sector device, this fails. > > > > > > > > If we round up rdev->sb_size to match the block size of > > > > the device, all IO will work correctly. > > > > > > > > Reported-by: "Liuhua Wang" <lwang@xxxxxxxx> > > > > Signed-off-by: NeilBrown <neilb@xxxxxxx> > > > > > > > > --- > > > > this issue has been discussed already a bit. See email thread > > > > Subject: Re: [PATCH] fix mirror device creation with lvcreate failed > > > > I think this is the best fix. It handles boths read and writes, and (I think) > > > > at the best level. > > > > > > > > Thanks, > > > > NeilBrown > > > > > > > > > > > > diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c > > > > index 4880b69e2e9e..31bdd73bc368 100644 > > > > --- a/drivers/md/dm-raid.c > > > > +++ b/drivers/md/dm-raid.c > > > > @@ -858,7 +858,8 @@ static int super_load(struct md_rdev *rdev, struct md_rdev *refdev) > > > > uint64_t events_sb, events_refsb; > > > > > > > > rdev->sb_start = 0; > > > > - rdev->sb_size = sizeof(*sb); > > > > + rdev->sb_size = roundup(sizeof(*sb), > > > > + bdev_logical_block_size(rdev->meta_bdev)); > > > > > > > > ret = read_disk_sb(rdev, rdev->sb_size); > > > > if (ret) > > > > > > Wouldn't it be better to use bdev_physical_block_size()? > > > > > > Even on a 4K device that emulates 512b logical sectors it is better to > > > use the physical block size (4K). > > > > > > _logical_ is the smallest value for which the IO actually works. > > And the goal of the change is to make it work. > > > > I don't object to using _physical_, but it isn't clear to me how I would > > justify that as "correct". > > > > A big question in my mind is: how much space does LVM reserve in this device > > for the metadata? It seems reasonable to assume that it reserves at least > > 1 logical block. If the API guarantees that at least one physical block is > > reserved, then that would justify using _physical_. > > I'll have to check with Jon and/or Heinz on this point. > > > A quick look at the code shows that the bitmap superblock is placed 4K after > > the start of the metadata. > > "the code" being the MD kernel code right? Any reason not to export a > #define that reflects the space MD reserves and just have dm-raid use that? No, "the code" being mddev->bitmap_info.offset = 4096 >> 9; /* Enable bitmap creation */ rdev->mddev->bitmap_info.default_offset = 4096 >> 9; in super_validate in dm-raid.c. i.e. dm-raid specific code. md doesn't reserve space, it just uses what it is told to. Told either by mdadm via the md superblock or by dm-raid. NeilBrown > > Starting to feel like hardcoding 4K is the right thing to do given the > current code.
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