[linux-lvm] Poison pills

[Stuart D. Gathman]

I have an old server with a VG named "rootvg".  (AIX roots showing.) I
just bought a new server, and it now has a volume group named "rootvg".
I plan to remove the disk from the old server, put it in a USB enclosure, 
and put it on the new server to access old files and use for backup.

To be safe, I will rename the volume grouip on the old machine first.  But 
I'm curious.  What would happen if I connected the PV with a duplicate VG 
name?  The VGIDs will be different, so hopefully the system will keep them 
separate somehow.  Will it refuse to activate the hot plugged VG because 
of the differing VGID?  Will it let me rename it without activating?

That brings up the subject of "poison pills".  Suppose I added a PV with a 
matching VGID?  That was created maliciously to mess up my system, or is 
just an old PV that I disconnected from the VG (before the vgreduce) that 
I forgot about.  Is this a poison pill?  It would have a unique PVID that 
is not listed in the metadata for the existing VG, but how does the system 
know which metadata to believe?  AIX used a "quorum" voting system to 
prevent accidental poison pills.  What happens in linux LVM?  If it sees 
two conflicting metadatas for the same VGID, what happens?

I think an inexpensive torture test of this logic is to get 3 or 4 external USB
drives, put them all in a VG, and start playing games with hotplugging them.
(E.g. unplug drive, vgreduce, plug drive back in).

-- 
	      Stuart D. Gathman <stuart at bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.