Re: [PATCH v2] md/raid0: add config parameters to specify zone layout

[Jason Baron]

On 4/24/20 7:22 PM, Song Liu wrote:
> 
> 
>> On Mar 30, 2020, at 9:00 AM, Jason Baron <jbaron@xxxxxxxxxx> wrote:
>>
>> Let's add some CONFIG_* options to directly configure the raid0 layout
>> if you know in advance how your raid0 array was created. This can be
>> simpler than having to manage module or kernel command-line parameters.
>>
>> If the raid0 array was created by a pre-3.14 kernel, use
>> RAID0_ORIG_LAYOUT. If the raid0 array was created by a 3.14 or newer
>> kernel then select RAID0_ALT_MULTIZONE_LAYOUT. Otherwise, the default
>> setting is RAID0_LAYOUT_NONE, in which case the current behavior of
>> needing to specify a module parameter raid0.default_layout=1|2 is
>> preserved.
>>
>> Cc: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>
>> Cc: NeilBrown <neilb@xxxxxxx>
>> Cc: Song Liu <songliubraving@xxxxxx>
>> Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
> 
> This patch looks good. However, I am not sure whether the user will 
> recompile the kernel for a different default value. Do you have real
> world use case for this?
> 
> Thanks,
> Song
> 

Hi Song,

Yes, we knew that all our raid0 arrays were created with >=3.14
kernels, and thus we wanted a way to specify the new layout without
needing to add to the command line or a module parameter. For us,
maintaining a CONFIG_* option is just simpler.

Thanks,

-Jason