Re: [PATCH 5/9] imsm: fix reserved sectors for spares

["Williams, Dan J" <dan.j.williams@intel.com>]

On Thu, Aug 25, 2011 at 7:14 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> Different OROMs reserve different amounts of space for the migration area.
> When activating a spare minimize the reserved space otherwise a valid spare
> can be prevented from joining an array with a migration area smaller than
> IMSM_RESERVED_SECTORS.
>
> This may result in an array that cannot be reshaped, but that is less
> surprising than not being able to rebuild a degraded array.
> imsm_reserved_sectors() already reports the minimal value which adds to
> the confusion when trying rebuild an array because mdadm -E indicates
> that the device has enough space.
>
> Cc: Anna Czarnowska <anna.czarnowska@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  super-intel.c |   11 ++++++++++-
>  1 files changed, 10 insertions(+), 1 deletions(-)
>
> diff --git a/super-intel.c b/super-intel.c
> index 0347183..193e0d0 100644
> --- a/super-intel.c
> +++ b/super-intel.c
> @@ -833,7 +833,16 @@ static struct extent *get_extents(struct intel_super *super, struct dl *dl)
>        struct extent *rv, *e;
>        int i;
>        int memberships = count_memberships(dl, super);
> -       __u32 reservation = MPB_SECTOR_CNT + IMSM_RESERVED_SECTORS;
> +       __u32 reservation;
> +
> +       /* trim the reserved area for spares, so they can join any array
> +        * regardless of whether the OROM has assigned sectors from the
> +        * IMSM_RESERVED_SECTORS region
> +        */
> +       if (dl->index == -1)
> +               reservation = MPB_SECTOR_CNT;

Anna rightly points out that this could probably be safely made
bigger.  As it stands this applies to too broad an array of disks.  I
think a happy medium (until we can nail down the forward compatibility
of older oroms, v8 in this case) is to detect the case where the disk
is being activated for rebuild and if it is at least as large as one
of the existing members truncate the reserved region to the same size
as the other member.  That way we are at least compatible with
whatever agent created the array in the first instance.

But this also comes back to the problem of duplicating the array
configuration.  It becomes difficult to make things the same size
unless the orom version (reserved region layout) is specified.

--
Dan

>
>        rv = malloc(sizeof(struct extent) * (memberships + 1));
>        if (!rv)
>
>
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