Re: [PATCH 1/1] Avoid OOPS when reshaping raid1 to raid0

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On Thu, 22 Mar 2012 17:15:53 +0100 Jes.Sorensen@xxxxxxxxxx wrote:

> From: Jes Sorensen <Jes.Sorensen@xxxxxxxxxx>
> 
> raid1 arrays do not have the notion of chunk size. Set the existing
> chunk size of the new raid0 to the same as the proposed new chunk size
> to avoid a divide by zero OOPS when aligning the size of the new array
> to that of the chunk size.

This oops happens in create_strip_zones at

		sector_div(sectors, mddev->chunk_sectors);

correct?

> 
> Signed-off-by: Jes Sorensen <Jes.Sorensen@xxxxxxxxxx>
> ---
>  drivers/md/raid0.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index 6f31f55..dff8d6b 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -639,6 +639,14 @@ static void *raid0_takeover_raid1(struct mddev *mddev)
>  	mddev->new_level = 0;
>  	mddev->new_layout = 0;
>  	mddev->new_chunk_sectors = 128; /* by default set chunk size to 64k */
> +	mddev->chunk_sectors = 128;	/*
> +					 * a raid1 one doesn't have the
> +					 * notion of chunk size, so set
> +					 * existing chunk_sector to match the
> +					 * new size to avoid divide by zero
> +					 * when aligning the size of the new
> +					 * raid0 to the existing chunk size.
> +					 */

But what if the RAID1 is not a multiple of 64K ?  Then you will lose
data.

We probably want the same thing we have in RAID5:



	chunksect = 64*2; /* 64K by default */

	/* The array must be an exact multiple of chunksize */
	while (chunksect && (mddev->array_sectors & (chunksect-1)))
		chunksect >>= 1;

	if ((chunksect<<9) < STRIPE_SIZE)
		/* array size does not allow a suitable chunk size */
		return ERR_PTR(-EINVAL);


??

Do you want to make a patch, or shall I?

Ofcouse, RAID0 have have non-power-of-2 chunk sizes, so we could just hunt
for a small factor... probably not worth it though.


Thanks,
NeilBrown

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