[libvirt-users] Working example of logical storage pool and volume creation?

[Justin Clift]

Hi all,

Does anyone have a working example of creation of a logical storage pool 
and volume?

I'm hitting a wall getting logical volumes to work on RHEL 6 beta.

There's a single drive I'm trying to setup (sdc) as a libvirt managed 
logical storage pool, but all volume creation on it fails.

Here's what I'm finding so far:

   Prior to any storage pool work, only the host boot drive (sda) is in lvm.

   # vgs
     VG       #PV #LV #SN Attr   VSize   VFree
     vg_host2   1   3   0 wz--n- 465.27g    0
   # pvs
     PV         VG       Fmt  Attr PSize   PFree
     /dev/sda2  vg_host2 lvm2 a-   465.27g    0
   # ls -la /dev/mapper
   total 0
   drwxr-xr-x.  2 root root    120 Jun  1 03:12 .
   drwxrwxrwt. 21 root root   3920 Jun  1 03:12 ..
   crw-rw----.  1 root root 10, 58 May 31 14:08 control
   lrwxrwxrwx.  1 root root      7 May 31 14:10 vg_host2-lv_home -> ../dm-7
   lrwxrwxrwx.  1 root root      7 May 31 14:08 vg_host2-lv_root -> ../dm-0
   lrwxrwxrwx.  1 root root      7 May 31 14:10 vg_host2-lv_swap -> ../dm-8
   #


   Creation of a logical storage pool, using sdc:

   # virsh pool-define-as guest_images_lvm logical - - /dev/sdc 
libvirt_lvm /dev/mapper
   Pool guest_images_lvm defined

   # virsh pool-info guest_images_lvm
   Name:           guest_images_lvm
   UUID:           17398035-8000-7252-ab25-58db95aed130
   State:          inactive

   # virsh pool-build guest_images_lvm
   Pool guest_images_lvm built

   #


   The physical device and volume group are seen in lvm:

   # pvs
     PV         VG          Fmt  Attr PSize   PFree
     /dev/sda2  vg_host2    lvm2 a-   465.27g      0
     /dev/sdc   libvirt_lvm lvm2 a-   465.76g 465.76g
   # vgs
     VG          #PV #LV #SN Attr   VSize   VFree
     libvirt_lvm   1   0   0 wz--n- 465.76g 465.76g
     vg_host2      1   3   0 wz--n- 465.27g      0
   #


   Starting the logical pool works:

   # virsh pool-start guest_images_lvm
   Pool guest_images_lvm started

   #


   Creation of volumes fail:

   # virsh vol-create-as guest_images_lvm volume1 8G
   error: Failed to create vol volume1
   error: internal error '/sbin/lvcreate --name volume1 -L 8388608K 
/dev/mapper' exited with non-zero status 3 and signal 0:   Volume group 
name expected (no slash)
   Run `lvcreate --help' for more information.

   #

So, it looked like "/dev/mapper" in the pool-define-as command should 
have instead been the LVM volume group again.  That doesn't work either 
though:

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

   # virsh pool-build guest_images_lvm
   Pool guest_images_lvm built

   # virsh pool-start guest_images_lvm
   Pool guest_images_lvm started

   # virsh vol-create-as guest_images_lvm volume1 8G
   error: Failed to create vol volume1
   error: cannot read path 'libvirt_lvm/volume1': No such file or directory

Looking in the libvirtd logs for this last attempt, the volume was 
actually successfully created.  But libvirtd then checks for it's 
presence (wrongly!), doesn't find it, and then lvremove's it:

   03:01:24.000: debug : virRunWithHook:832 : /sbin/lvcreate --name 
volume1 -L 8388608K libvirt_lvm
   ...
   03:01:24.223: debug : virRunWithHook:848 : Command stdout:   Logical 
volume "volume1" created
   ...
   03:01:24.223: error : virStorageBackendLogicalCreateVol:616 : cannot 
read path 'libvirt_lvm/volume1': No such file or directory
   ...
   03:01:24.223: debug : virRunWithHook:832 : /sbin/lvremove -f 
libvirt_lvm/volume1


Guessing I'm either doing something wrong, or hitting bugs, or ?

Anyone have ideas/suggestions/etc?

Regards and best wishes,

Justin Clift

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