Bug#641584: mdadm-raid does not assemble mds on multipath devices

[NeilBrown]

On Wed, 14 Sep 2011 19:48:23 +0400 Michael Tokarev <mjt at tls.msk.ru> wrote:

> On 14.09.2011 18:16, martin f krafft wrote:
> >> Since mdadm and multipath-tools do not depend on each other in
> >> their init.d LSB headers, insserv sorts mdadm-raid before
> >> multipath-tools-boot. This prevents the assembly of MDs on
> >> multipath devices.
> > 
> > I do not have experience with multipath, hence my question:
> > I understand you want to assemble MDs on multipath devices. Is this
> > the only sensible stacking? Or is it plausible to have multipath
> > devices on MDs?
> 
> Yes this is the only sensible stacking - component devices on
> multipath, md on top of it.  So it is the right fix too -- to
> have another init order dependency on multipath-tools-boot.
> 
> > mdadm can also handle multipath devices. Is this the same thing?
> 
> No it is not.  md amd dm subsystem has several common components.
> This is dm multipath - the one which is actually used, with good
> tools written for it.  mdadm is not there yet, and it is not
> widely used for this purpose.

Completely agree except for the word 'yet'.  It seems to imply that md might
improve in support for multipath.
This is not the case.  multipath in md is just wrong and will not be extended.
dm-multipath is the only multipath that anyone should use.

Thanks,
NeilBrown
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