Re: Grow set size issue

[Jes Sorensen <jes.sorensen@gmail.com>]

On 03/29/2017 05:34 PM, NeilBrown wrote:
> On Thu, Mar 30 2017, jes.sorensen@gmail.com wrote:
>
>> Hi Neil,
>>
>> In the below patch you changed the error handling, to make the kernel
>> not setting the size of the device being an error. However we still have
>> the code in place to handle the error, except it never triggers.
>
> So we do.  I should have removed all of that.
> I should have just reverted
> Commit: 65a9798b58b4 ("FIX: Detect error and rollback metadata")
>
>
>>
>> Question is do you remember the reason for this change? Old kernels not
>> allowing it, are there any legitimate reasons for the kernel to refuse
>> the size change?
>
> I needed to go further back to remind myself why we do these size change
> at all.
> The command being run here is "mdadm --grow /dev/mdX --size=foo"
> which has a primary purpose of changing the component_size of the array.
> What can happen is that someone makes all the components bigger
> (E.g. with LVM) and then uses this command to set --size=max, and it
> doesn't work.  That is because md doesn't know the devices are bigger.
>
> You can tell md that devices have changes size by writing to the "size"
> attribute.
> mdadm doesn't have an option for doing that per-device - you need to
> poke into sysfs.
>
> To make it a bit easier, when you use "--grow --size=foo", mdadm will
> always write "foo" to the "size" attribute of each device, just incase
> that will be helpful. In the case where the device is now bigger, it
> will.
>
> In the case where the size of the array is being reduced, it is not
> permitted to change the "size" of each device until the "component_size"
> of the array has changed, so these attempts to change "size" will fail.
> But that isn't a problem.
>
> In short, the attempt to change "size" here is a convenience, and
> optimization.  It doesn't matter if it fails.
>
> So please just revert all bits of the above commit that are still
> present.

Hi Neil,

Thanks for the explanation, I'll take the big hammer to the leftovers 
and get rid of them.

Cheers,
Jes