Re: How to recover after md crash during reshape?

[Phil Turmel <philip@turmel.org>]

On 10/21/2015 04:26 PM, Neil Brown wrote:
> Phil Turmel <philip@turmel.org> writes:

>> Hmmm.  This feature has advanced beyond my last look at the code.  I was
>> under the impression the backup option was only optional when mdadm
>> could move the data offset.  Does this new algorithm apply to v0.90
>> metadata, a v3.2 kernel, and v3.2.5 mdadm?
>>
> 
> It isn't a new algorithm, it is the original algorithm.
> 
> In mdadm-2.4-pre1 (march 2006), you couldn't specify a backup file, but
> you could grow a raid5 to more devices.
> That was changed by a patch with comment:
> 
>     Allow resize to backup to a file.
>     
>     To support resizing an array without a spare, mdadm now understands
>       --backup-file=
>     which should point to a file for storing a backup of critical data.
>     This can be given to --grow which will create the file, or
>     --assemble which will restore from the file if needed.
>     
> The backup-file was subsequently used to support in-place reshapes and
> array shrinking.

Ah, ok.  I wasn't using parity raid that far back, and never noticed
that growing to more devices worked that way.

Thanks for clarifying.

Phil