On Mon, Apr 20, 2009 at 03:23:52PM +1000, Neil Brown wrote:
> How does LVM manage metadata??? I assume it stored the metadata on
> the device. Which is what mdadm does.
It stores a backup of the metadata under /etc after every changes it
makes. It is like if "mdadm --create" have automatically added the array
to /etc/mdadm.conf etc.
> But as devices can move between machines.....
With LVM, moving a volume group means running
vgchange/vgexport/pvscan/vgimport/vgchange, so it's not like "it just
works". So if there are any name conflicts, you must explicitely run
vgrename before the new VG can be activated.
> > 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
But that requrires the MD device to already be present therefore does
not help solving the name clash issue.
What I propose is that "mdadm --assemble" should accept "UUID=..."
instead of the MD device name. Then mdadm could ignore the
name/homehost, and create the device node with a name
(/dev/md/by-uuid/...) that will never clash with arrays using
traditional names.
Gabor
--
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MTA SZTAKI Computer and Automation Research Institute
Hungarian Academy of Sciences
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