Re: [Patch] mdadm ignoring homehost?

[Neil Brown <neilb@suse.de>]

On Friday April 17, gombasg@sztaki.hu wrote:
> On Fri, Apr 17, 2009 at 01:49:41PM +1000, Neil Brown wrote:
> 
> > As you probably know, my preferred solution is to have all arrays
> > listed in /etc/mdadm.conf.  If it isn't in mdadm.conf, it doesn't get
> > assembled.   But I don't have a lot of company in this opinion.  Lots
> > of people want to have arrays assembled without them being in
> > mdadm.conf, and I'm trying to work with that.
> 
> IMHO the goal to have all arrays defined in mdadm.conf would be much
> better to achieve if mdadm managed that configuration itself, not unlike
> how LVM metadata is handled. Of course doing that right is not exactly
> easy...

How does LVM manage metadata???  I assume it stored the metadata on
the device.  Which is what mdadm does.
But as devices can move between machines.....

> 
> > Note that 0.90 metadata does contain homehost information to some
> > extent.  When homehost is set, the last few bytes of the uuid is set
> > from a hash of the homehost name.  That makes it possible to test if a
> > 0.90 array was created for 'this' host, but not to find out what host
> > it was created for.  So the above expedient won't work for 0.90
> > arrays, but the rest of the homehost concept (including any possible
> > 'homehost=any' option) does.
> 
> How about introducing /dev/md/by-uuid/... (or similar) and teaching
> people that if they want to transparently carry their arrays from one
> host to another, then they should always refer to it by UUID?

This already exists, though it might be distro-dependant.
  /dev/disk/by-id/md-uuid-xxxxx

> 
> Mounting file systems by UUID instead of device path got accepted by
> people who really care about moving things around, so doing the same for
> RAID could also work.

That would be nice... 

NeilBrown