Re: [PATCH] FIX: Do not count as backup devices, spare disks used for reshape

[NeilBrown <neilb@suse.de>]

On Fri, 18 Mar 2011 11:55:12 +0100 Adam Kwolek <adam.kwolek@intel.com> wrote:

> Problem:
> Reshape is run without specified backup file when all spares are used for expansion.
> 
> When spare disks are used for reshape, they should not be counted as backup devices.
> Md still thinks about them as about spares until reshape will not be started.
> mdadm should have all it in mind.
> 
> Signed-off-by: Adam Kwolek <adam.kwolek@intel.com>
> ---
> 
>  Grow.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/Grow.c b/Grow.c
> index b639585..17c22fc 100644
> --- a/Grow.c
> +++ b/Grow.c
> @@ -1660,6 +1660,7 @@ static int reshape_array(char *container, int fd, char *devname,
>  	unsigned long long array_size;
>  	int done;
>  	struct mdinfo *sra = NULL;
> +	int used_spares = 0;
>  
>  	/* when reshaping a RAID0, the component_size might be zero.
>  	 * So try to fix that up.
> @@ -1793,6 +1794,7 @@ static int reshape_array(char *container, int fd, char *devname,
>  					 * be part of the array.
>  					 */
>  					add_disk(fd, st, info2, d);
> +					used_spares++;
>  				}
>  			}
>  			sysfs_free(info2);
> @@ -1956,7 +1958,7 @@ started:
>  				Name ": %s: Cannot grow - need backup-file\n", 
>  				devname);
>  			goto release;
> -		} else if (sra->array.spare_disks == 0) {
> +		} else if (sra->array.spare_disks - used_spares == 0) {
>  			fprintf(stderr, Name ": %s: Cannot grow - need a spare or "
>  				"backup-file to backup critical section\n",
>  				devname);


This change doesn't make sense to me.

The only time when we use a spare device as for storing the backup is (or at
least should be) when increasing the number of devices in the array.
In that case we only need a backup at the very beginning.
So we use the end of a spare for the backup that happens at the every
beginning and it all works happily.

Why do you now want to count a spare used for backup as a spare to use for
growth?

NeilBrown