[CentOS] interesting kvm lvm collision issue

Iain Morris iain.t.morris at gmail.com
Mon Oct 25 15:31:40 EDT 2010


I've been running into a reproducible problem when using default LVM volume
group names to present block devices for virtual machines in KVM, and I'm
wondering why it is happening.

On dom0 I make a default VolGroup00 for the operating system.  I make a
second VolGroup01 for logical volumes that will be block devices for virtual
systems.

In VolGroup01, I make two lv's for one system: lv.sys1, and lv.sys1-data.

I then build a new virtual machine called sys1, using lv.sys1 for the root
filesystem, and lv.sys1-data for an independent data partition.  Everything
works great after installation, and vgdisplay on both systems looks great.

If I then run vgscan, however, on the host system, it picks up the
VolGroup01 I created _within_ the virtual machine, so I now have 2
VolGroup01's with different UUIDs showing up on dom0.

Now I can see how vgscan would mistakenly see the VolGroup01 of sys1 on the
block device lv.sys1-data, but why are the VolGroup00 vg's not colliding as
well?

When a pvdisplay is run, I have a new "physical volume" that is actually
just a logical volume of the original VolGroup01:

[root at iain2 ~]# pvdisplay
  WARNING: Duplicate VG name VolGroup01: Existing
FNiKc9-BB3t-ziMg-prWW-n8RA-OMzk-obiKnf (created here) takes precedence over
C8fNMV-aeSW-syIn-fWJZ-vJdK-N0As-Itrvfi
  WARNING: Duplicate VG name VolGroup01: Existing
FNiKc9-BB3t-ziMg-prWW-n8RA-OMzk-obiKnf (created here) takes precedence over
C8fNMV-aeSW-syIn-fWJZ-vJdK-N0As-Itrvfi
  --- Physical volume ---
  PV Name               /dev/VolGroup01/lv-sys1-data
  VG Name               VolGroup01
  PV Size               40.00 GB / not usable 4.00 MB
  Allocatable           yes (but full)
  PE Size (KByte)       4096
  Total PE              10239
  Free PE               0
  Allocated PE          10239
  PV UUID               FTA4QU-ydZ7-e2Yy-nBsi-t4st-3jj7-IAkQH8

  --- Physical volume ---
  PV Name               /dev/sda3
  VG Name               VolGroup00
  PV Size               39.06 GB / not usable 29.77 MB
  Allocatable           yes (but full)
  PE Size (KByte)       32768
  Total PE              1249
  Free PE               0
  Allocated PE          1249
  PV UUID               tTViks-3lBM-HGzV-mnN9-zRsT-fFT0-ZsJRse

  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               VolGroup01
  PV Size               240.31 GB / not usable 25.75 MB
  Allocatable           yes
  PE Size (KByte)       32768
  Total PE              7689
  Free PE               5129
  Allocated PE          2560
  PV UUID               ZE5Io3-WYIO-EfOQ-h03q-zGdF-Frpa-tm63fX



Has anyone experienced this?  It's very unnerving to know your data is
intact as you add new logical volumes for kvm systems.  I suppose the lesson
learned here is to provide VGs with specific host names.



-- 
-- -
Iain Morris
iain.t.morris at gmail.com
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