Re: problems with lots of arrays

[Shaohua Li <shli@kernel.org>]

On Wed, May 11, 2016 at 08:39:53AM +1000, NeilBrown wrote:
> On Wed, May 11 2016, Jes Sorensen wrote:
> 
> > Mike Lovell <mike.lovell@endurance.com> writes:
> >> we have a number of systems that have a large number of software
> >> arrays running. its in the couple hundred range. we have been using a
> >> custom built kernel based on 3.4 but are wanting to update to a
> >> mainline kernel and have been experimenting with 4.4. the systems are
> >> running recent centos 6 releases but we have been downgrading the
> >> mdadm version from 3.3.2 in 6.7 to a custom build 3.2.6. we installed
> >> the downgraded version due to a problem with array numbering. i
> >> emailed the list a while ago explaining the issue and submitting a
> >> patch to fix [1]. i never heard anything back and since we had a
> >> simple fix i didn't follow up on it.
> >
> > [snip]
> >
> >> what do you all think?
> >>
> >> thanks
> >> mike
> >>
> >> [1] http://marc.info/?l=linux-raid&m=142387809409798&w=2
> >
> > Staying consistent in using dev_t rather than casting back and forth to
> > int seems a reasonable fix to apply to mdadm. It obviously won't change
> > the issues with the newer kernels, but I don't see any reason why we
> > shouldn't apply that fix to mdadm.
> >
> > Neil any thoughts on this?
> 
> I agree that changing "int" to "dev_t" is a good idea.
> 
> We should really fix the more general problem too.
> 
> On any kernel with  /sys/module/md_mod/parameters/new_array
> find_free_devnm avoid trying anything above 511. (1<<9)-1.
> 
> If that fails to find a free number, then it should probably try a name
> like "md_NN" and act as though ci->name is set.
> 
> Also, when a "name" given for the md array that is longer than 28 bytes
> we need to fall back to choose an array name ourselves even if ci->name
> is set.  Start with md_512 and work upwards.
> Rather than probing we should read /sys/block looking for "md_*" and
> maybe choose 1 more than the largest number found.

I'm wondering why udev open the device with major/minor without checking if the
device exists. A simple 'stat' check is neat.

Thanks,
Shaohua