On Fri, Sep 22, 2023 at 10:36 AM Stan Liao <StanL@xxxxxxxxxxxxxx> wrote:
>
> Xiao Ni wrote:
> > On Thu, Sep 21, 2023 at 11:22 AM Stan Liao <StanL@xxxxxxxxxxxxxx> wrote:
> > >
> > > Hi,
> > > A md-raid (level 1) is created with 5 nvme drives and the metadata version
> > is specified as 1.2. The following command is used.
> > > sudo mdadm --create /dev/md0 --level=1 --raid-devices=5
> > > /dev/nvme{1,2,3,4}n1 /dev/nvme4n2 --metadata=1.2 The capacities of
> > nvme{1,2,3,4}n1 and nvme4n2 are 3.2TB, 1.92TB, 3.2TB, 512GB, and 512GB.
> > > OS: 20.04.1-Ubuntu
> > > mdadm version: v4.1 - 2018-10-01
> > > After creation, we found that the size of the bitmap_super_t and internal
> > bitmap is 16KB (this is concluded by observing FF value is filled from around
> > byte offset 0x100 of LBA 0x10 to byte offset 0x1FF of LBA 0x1F), but the
> > mdp_superblock_1.bblog_offset value is 0x10. As a result, the
> > mdp_superblock_1 occupies LBA 0x08 ~ 0x0F; bitmap_super_t and internal
> > bitmap occupy LBA 0x10 ~ 0x20; bblog occupies LBA 0x18 ~ 0x20.
> > > If bblog and bitmap do overlap, I would like to know the size value used to
> > calculate bitmap size and bblog_offset. The size value used to calculate
> > bitmap size and bblog_offset is mdp_superblock_1.size or
> > mdp_superblock_1.data_size? Thanks a lot.
> > >
> >
> > Hi
> >
> > For super1.2 the layout should be:
> > | 4KB | 4KB | bitmap space | head room |
> > data |
> >
> > The first 4KB is empty from the beginning of the disk. The second 4KB is for
> > md superblock. Then is bitmap suerblock. So if you want to see the content
> > of bitmap_super_t, the offset should be 0x2000?
> >
> > Regards
> > Xiao
>
> Right. The bitmap_super_t is at offset 0x2000 (absolute LBA address 0x10).
> And mdadm write bitmap_super_t and bitmap from LBA 0x10 to LBA 0x1F.
> Including bblog, super1.2 layout would be:
> | 4KB | 4KB | bitmap space | bblog | head room | data |
> We observe the bblog_offset value, which resides in mdp_superblock_1, is 0x10.
> So we think there is an overlap between bitmap and bblog.
>
Because the bblog_offset is based on the start of superblock. So if
you want to calculate the offset based on the start of the disk, it
needs to add 4KB on bblog_offset. Now your bblog_offset is 0x10. It
means from the start of the superblock, it's 4K(superblock) +
4K(bitmap space). So your raid only has one page, right?
You can also you mdadm -E $member to check the "Bad Block Log"
Regards
Xiao
