[libvirt] [libvirt-users] LVM Volume Creation

Ján Tomko jtomko at redhat.com
Tue Jul 15 07:15:35 UTC 2014

On 07/15/2014 08:28 AM, Ravi Samji wrote:
> Hi All,
> I'm having issue with creating LVM Volume via libvirt.
> We are running libvirtd 1.2 with KVM.
> We are creating Volume Group (VG01) outside of libvirt and defining a storage pool for it.
> Here is the StoragePool XML for the Volume Group created outside libvirt.
> <pool type="logical">
>     <name>VG01</name>
>     <target>
>         <path>/dev/VG01</path>
>     </target>
> </pool>
> We are creating Logical Volume (ub_test01.img) through libvirt in the Volume Group (VG01)
> Here is the XML to create Storage Volume in LVM Storage Pool VG01.
> <volume type="block">
>     <name>ub_test01.img</name>
>     <allocation>0</allocation>
>     <capacity unit="M">1</capacity>

If the allocation is not equal to the capacity, libvirt calls lvcreate with
the --virtualsize option, which creates this snapshot that should take up less

For a regular volume, just omit the allocation element, or use the same values
for both.

>     <target>
>         <format type="lvm2" />
>     </target>
> </volume>
> When I create the Logical Volume from libvirt using above XML and run lvs command to list logical volumes, this is what I see.
> LV		VG	Attr	LSize	Origin			Snap%	Move	Log	Copy%	Convert
> --------------- ------- ------- ------- ----------------------- ------- ------- ------- ------- -------
> foo		VG01	-wi-a-	  1.00g
> ub_test01.img	VG01	swi-a-	  4.00m	[ub_test01.img_vorigin]	0.20
> root		ops-02	-wi-ao	227.08g
> swap_1		ops-02	-wi-ao	  5.75g
> As you see, ub_test01.img shows that it has an Origin indicating that it was created as a snapshot, but, that Origin doesn't exist and wasn't specified.
> I'd appreciate if you anyone can help me understand what is going on and/or describe how to make libvirt create logical volumes not as a snapshot.
> I'm happy to enable debugging to see what command libvirt is running to create the volume if someone case describe how to enable debugging.

See http://libvirt.org/logging.html


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