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I have a machine setup with Centos6 as a virtualisation host. It has a single 250G hard drive that is configured as a single lvm volume group(vg_fluke). Now I would like to use the host's lvm as a storage pool for KVM.

I found this question on SF and method one describes what I would like to achieve. But I can't find a way to go about it.

I tried the following, but since the documentation is sketchy, I am certain that I am doing something wrong.

virsh # pool-define-as guest_images_lvm logical - - - - /dev/vg_fluke
Pool guest_images_lvm defined

And followed it with,

virsh # pool-start guest_images_lvm
error: Failed to start pool guest_images_lvm
error: internal error Child process (/sbin/vgchange -ay -) status unexpected: exit status 5

More Information on the LVM setup:

[root@fluke ~]# pvs
  PV         VG       Fmt  Attr PSize   PFree  
  /dev/sdb2  vg_fluke lvm2 a--  232.39g 125.45g
[root@fluke ~]# lvs
  LV      VG       Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  lv_home vg_fluke -wi-ao   5.00g                                      
  lv_root vg_fluke -wi-ao 100.00g                                      
  lv_swap vg_fluke -wi-ao   1.94g                                      
[root@fluke ~]# vgs
  VG       #PV #LV #SN Attr   VSize   VFree  
  vg_fluke   1   3   0 wz--n- 232.39g 125.45g


Followed @sitaktif's advice and now get the following error:

virsh # pool-define-as lv_guest_vm logical --target /dev/vg-main
Pool lv_guest_vm defined

virsh # pool-start lv_guest_vm
error: Failed to start pool lv_guest_vm
error: internal error '/sbin/vgchange -ay lv_guest_vm' exited with non-zero status 5 and signal 0:   Volume group "lv_guest_vm" not found

Note: I am on trying this on a different machine where the VG is vg-main. Do I have to create a second VG for libvirt to use for virtual machines? How can I set it up use a LV in the existing VG?

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The following command is incorrect:

virsh # pool-define-as guest_images_lvm logical - - - - /dev/vg_fluke

...because it executes:

/sbin/vgchange -ay -

...instead of:

/sbin/vgchange -ay /dev/vg_fluke

Just explicitely name the parameter instead of using dashes:

pool-define-as guest_images_lvm logical --target /dev/vg_fluke

That should solve your problem.

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Thanks for reply. I just got around to trying it, but there is a new error now. I updated the question with the relevant details. – Shoan Apr 26 '12 at 12:51

By default, libvirt uses the pool name as the name of the vg. You can see it's doing that with the /sbin/vgchange -ay lv_guest_vm command that it tried to execute. Just do:

pool-define-as lv_guest_vm logical --source-name vg-main --target /dev/vg-main

and it should work.

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