On Tue, Dec 21, 2021 at 9:56 PM Mariusz Tkaczyk
[off-list ref] wrote:

Hi Xiao,
On Tue, 21 Dec 2021 09:40:50 +0800
Xiao Ni [off-list ref] wrote:

quoted

Now for a raid0, it can't remove one member disk from raid0. It
returns EBUSY and the raid0 still can work well. It makes sense.
Because all member disks are busy, the admin can't remove the member
disk and mdadm gives a proper error.

EBUSY means that drive is busy but it is not. Just drive cannot be
safety removed. As I wrote in patch 2:

If "faulty" was not set then -EBUSY was returned to
userspace. It causes that mdadm expects -EBUSY if the array
becomes failed. There are some reasons to not consider this mechanism
as correct:
- drive can't be failed for different reasons.
- there are path where -EBUSY is not reported and drive removal leads
to failed array, without notification for userspace.
- in the array failure case -EBUSY seems to be wrong status. Array is
not busy, but removal process cannot proceed safe.

For compatibility reasons i cannot remove EBUSY. I left more detailed
explanation in patch 2.

quoted

With this patch, it changes the situation. In raid0_error, it sets
MD_BROKEN. In fact, it isn't broken. So is it really good to set
MD_BROKEN here? In patch 62f7b1989c0 ("md raid0/linear: Mark array as
'broken'...), MD_BROKEN is introduced
when the member disk disappears and the disk is really broken. For
raid0/linear, the raid device can't work anymore.

It is broken, any md_error() call should end with appropriate action:
- drive removal (if possible)
- failing array (if cannot degrade array)

We cannot trust drive if md_error() was called, so writes will be
blocked. IMO it is reasonable- to not engage level stack, because one
or more members cannot be trusted (even if it is still accessible). Just
allow to read old data (if still possible).

Thanks for the explanation. It's ok for me. Just want to have the same
understanding. Now raid0 works
in the way that it will fail when calling md_error.

Regards
Xiao