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Re: [linux-lvm] Just for information ....

On Tue, Nov 20, 2001 at 03:06:38PM -0700, Andreas Dilger wrote:
> On Nov 20, 2001  21:41 +0100, Wichert Akkerman wrote:
> > Previously Andreas Dilger wrote:
> > > Yes.  You will need to do a vgscan to find the new disks.  Hopefully they
> > > will not have the same VG name as another VG on that system.
> > 
> > What if they do?
> Then it will depend on disk ordering which one you get under that name, and
> the other will be unavailable.  vgscan will see all of the disks, but then
> start checking the UUIDs on the PVs against the list on the "first" disk,
> and the extra disks with UUIDs that don't match will be discarded.

Worst case would be a temporary disconnect of the PVs belonging to one
of the VGs which share the same name. vgscan+vgrename the found one and
reconnect the drives and vgscan again.

> I don't think there are any likely scenarios with LVM 0.9+ that will cause
> problems, but since UUIDs were only introduced in 0.9, it may be much harder
> to handle this in older LVM versions.

See above.

> You might be able to vgexport the disks from the "other" VG at that time,
> and reimport it with a different name, but I don't know how reliable that
> will be (if it even works).  LVM has been confused by less.


> Better to just
> "not do that" in the first place.
> FYI, AIX LVM does not keep the VG name on the disk itself, only a UUID.
> You also never do something like "vgscan" at boot time to reconfigure
> the LVM setup.  When you attach the disks to a new system, you have to
> import them (at which point they get a name that is stored in a config
> file in /etc), and your LVM config is never touched until you change it.
> When you export the VG, it also doesn't write to the disks, just deletes
> the config from /etc.  This means you don't need to do anything to the
> VG before moving it to another system.

Well, actually you can just "vgscan" in the VG without vgexport'ing it
in Linux LVM as well. vgexport/vgimport exactly is the clean procedure
to make sure that name clashes don't happen!

> Cheers, Andreas
> --
> Andreas Dilger
> http://sourceforge.net/projects/ext2resize/
> http://www-mddsp.enel.ucalgary.ca/People/adilger/
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> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html


Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***


Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
Mauelshagen Sistina com                           +49 2626 141200
                                                       FAX 924446

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