Re: [PATCH] md/raid10: prioritize adding disk to 'removed' mirror

[Song Liu]

On Mon, May 29, 2023 at 6:14 AM Li Nan <linan666@xxxxxxxxxxxxxxx> wrote:
>
>
>
> 在 2023/5/29 21:00, Yu Kuai 写道:
> > Hi,
> >
> > 在 2023/05/27 17:20, linan666@xxxxxxxxxxxxxxx 写道:
> >> From: Li Nan <linan122@xxxxxxxxxx>
> >>
> >> When add a new disk to raid10, it will traverse conf->mirror from start
> >> and find one of the following mirror to add:
> >>    1. mirror->rdev is set to WantReplacement and it have no replacement,
> >>       set new disk to mirror->replacement.
> >>    2. no mirror->rdev, set new disk to mirror->rdev.
> >>
> >> There is a array as below (sda is set to WantReplacement):
> >>
> >>      Number   Major   Minor   RaidDevice State
> >>         0       8        0        0      active sync set-A   /dev/sda
> >>         -       0        0        1      removed
> >>         2       8       32        2      active sync set-A   /dev/sdc
> >>         3       8       48        3      active sync set-B   /dev/sdd
> >>
> >> Use 'mdadm --add' to add a new disk to this array, the new disk will
> >> become sda's replacement instead of add to removed position, which is
> >> confusing for users. Meanwhile, after new disk recovery success, sda
> >> will be set to Faulty.
> >>
> >> Prioritize adding disk to 'removed' mirror is a better choice. In the
> >> above scenario, the behavior is the same as before, except sda will not
> >> be deleted. Before other disks are added, continued use sda is more
> >> reliable.
> >>
> >
> > I think this change make sense, however, it's better to do this for all
> > personality instead of just for raid10.
> >
> > Thanks,
> > Kuai
>
> raid5 is currently like this. If others are OK with this changes to
> raid10, I will modify raid1 later.

This change looks reasonable. Could you please add a mdadm test
to cover this case?

Applied to md-next.

Thanks,
Song