Re: mdadm --detail works, mdadm --stop says "does not appear to be an md device"

[Marc MERLIN <marc@merlins.org>]

On Mon, Mar 20, 2023 at 04:16:59PM +0100, Mariusz Tkaczyk wrote:
> On Mon, 20 Mar 2023 07:50:35 -0700
> Marc MERLIN <marc@merlins.org> wrote:
> 
> > On Mon, Mar 20, 2023 at 03:36:39PM +0100, Mariusz Tkaczyk wrote:
> > > Hi,
> > > mdadm is unable to complete this task because it cannot ensure that it is
> > > safe to stop the array. It cannot open the array with O_EXCL.
> > > If it is mounted then it may hang if filesystem needs to flush some data.  
> >  
> > Thanks for the reply. The array was not mounted, that said, given that
> > it was fully down, there wasn't a way to flush the data if it had been
> > (cable problem to an enclosure, all the drives disappeared at once)
> > 
> > > Please, try umount the array if it mounted somewhere and then try:
> > > 
> > > # echo inactive > /sys/block/md6/md/array_state
> > > # echo clear > /sys/block/md6/md/array_state  
> > 
> > I can try this next time (already had to reboot), thanks.
> > 
> > That said, mdadm should output a better message in this case
> > > > mdadm: /dev/md6 does not appear to be an md device  
> > is clearly wrong 
> > 
> > Is that something easy to fix/improve?
> 
> Oh, sorry my bad, please see the code:
> https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/tree/mdopen.c#n472
> 
> We are failing to "understand" the array:
> https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/tree/util.c#n229
> It has nothing to do with open and O_EXCL. I didn't dig into to determine why.
> 
> Anyway, now error seems to be reasonable but maybe we should be able to tract
> this array as valid? I requires more work and analysis so it is not simple fix.

You are definitely more knowledgeable about this than I am.
All I can say is that the array was down, not mounted, and I couldn't
stop it without a reboot, and that's a problem.

Any way to force stop in a case like this, would be quite welcome :)

Thanks,
Marc
-- 
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